Given a data file (text file or data.frame) with the
correct variable names (see section 1.3) and a model file (see section
1.1 and 2) the steps needed to fit either an exponential RT-MPT model
(Hartmann et al., 2020; Hartmann & Klauer, 2020; Klauer &
Kellen, 2018) or a diffusion RT-MPT model (Klauer et al., submitted) to
the data is described in Section 1:
1.1 Convert the equation/model file to an ertmpt_model
or drtmpt_model via the to_ertmpt_model() or
to_drtmpt_model() function 1.2 If necessary, specify some
restrictions 1.3 Convert the data file to an ertmpt_data or
drtmpt_data object via the to_ertmpt_data() or
to_drtmpt_data() function 1.4 Fit the specified model to
the data via the fit_ertmpt() or fit_drtmpt()
function 1.5 Check convergence of the model parameters and getting a
summary
In Section 2, 3, and 4 more information about the equation/model files, the data and additional functions is provided.
The equation/model file can be provided by a text file or directly
like the following. One might use a syntax that is comparable to the
EQN syntax by Heck, Arnold, and Arnold (2018) or Hu (1999)
or a syntax that is comparable to the MDL syntax by
Singmann and Kellen (2013). In the EQN syntax you can
separate trees, categories and paths either by using semicolons (like in
the example below) or commas, but not mixed:
eqn = "
# CORE MODEL
## EQN SYNTAX
## tree ; cat ; mpt
0 ; 0 ; Do
0 ; 0 ; (1-Do)*g
0 ; 1 ; (1-Do)*(1-g)
1 ; 3 ; Dn
1 ; 2 ; (1-Dn)*g
1 ; 3 ; (1-Dn)*(1-g)
"In this eqn object we specify a Two-High Threshold (2HT)
model. Comments can be done with a # symbol at the
beginning of a line.
The same model can be specified with the MDL syntax:
mdl = "
# CORE MODEL
## MDL SYNTAX
### targets
Do+(1-Do)*g
(1-Do)*(1-g)
### lure
(1-Dn)*g
Dn+(1-Dn)*(1-g)
"All paths/branches that lead to the same response category will be
added together with a + symbol.
More information about these two syntaxes are written in Section 2.
The conversion to an ertmpt_model or
drtmpt_model list can then be done by the
to_ertmpt_model() or to_drtmpt_model(),
respectively, function:
library(rtmpt)
# MAKING AN ERTMPT MODEL
# using the MDL syntax:
e2HTM <- to_ertmpt_model(mdl_file = mdl)
# using the EQN syntax:
e2HTM <- to_ertmpt_model(eqn_file = eqn)
e2HTM##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus NA NA NA
## plus NA NA NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 0 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------# MAKING A DRTMPT MODEL
# using the MDL syntax:
d2HTM <- to_drtmpt_model(mdl_file = mdl)
# using the EQN syntax:
d2HTM <- to_drtmpt_model(eqn_file = eqn)
d2HTM##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 0 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 0 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Next we discuss model restrictions for an ertmpt_model
(1.2.1) and a drtmpt_model (1.2.2), and the response
mapping if more than one encoding plus motor execution time is wanted
(1.2.3).
There are four functions with which the process parameters of an
ertmpt_model object can be changed. Two functions can be
used to hold a process probability parameter (theta) constant or to make
some process probability parameters equal. Two functions can be used to
suppress process completion times (taus), which means the process times
are set to zero, or to make some process completion times equal.
To hold a process probability constant you can use
theta2const() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA NA 0.5
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 1 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus NA NA NA
## plus NA NA NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 0 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Here, "g" will be set to 0.5 and will, therefore, not be
estimated. You might also use this function with a vector of
names (and a vector of constants). Note that
the new model is not saved because we did not assign it to an R
object.
An alias for this function is set_theta_const().
To set two or more process probabilities equal, you can use
theta2theta() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA Dn NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 1 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus NA NA NA
## plus NA NA NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 0 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------The process probabilities for all processes specified in
names are set equal. The first of the process
names in alphabetical order (here "Dn")
denotes the reference probability that will be estimated. The other(s)
will not be estimated but will be set to be equal to the reference
process probability. The keep_consts argument can be used,
if you want to keep constants that you already specified and all other
process probabilities should have the same constant, but we suggest to
use theta2const() for that.
An alias for this function is set_thetas_equal().
To suppress a process completion time (i.e., set it to zero) you can
use tau2zero() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus NA NA 0
## plus NA NA NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 1 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Here, the process completion time of "g" with outcome
"minus" (meaning the time for 1-g) is set to zero and,
therefore, will not be estimated (which typically does not make sense to
do). Also this function can be used with vectors.
An alias for this function is set_tau_zero().
To set two or more process completion times with the same outcome
equal you can use theta2theta() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus <NA> Dn NA
## plus <NA> <NA> NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 0 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------The process completion times for all processes specified in
names are set equal (i.e., all process completion times in
minus-direction will be equal, but all process completion times in
plus-direction will still be estimated, unless you set
outcome to “both”). The first of the process
names in alphabetical order (here "Dn")
denotes the reference process times in minus direction (and/or plus
direction) that will be estimated. The other(s) will not be estimated,
but will be set to be equal to the reference process time(s). The
keep_zeros argument can be used, if you want to keep the
zeros that you already specified and all other process times with the
same outcome should be zero as well. Also here we suggest using the
tau2zero() function.
An alias for this function is set_taus_equal().
There are six functions with which the process parameters of a
drtmpt_model object can be changed. Three functions can be
used to set some process parameters to constants and three functions can
be used to make some process parameters equal.
To hold a process threshold constant you can use
a2const() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA 1
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 1 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 0 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Here, the threshold for "g" will be set to 1.0 and,
therefore, will not be estimated. You might also use this function with
a vector of names (and a vector of constants).
Note that the new model is not saved because we did not assign it to an
R object.
An alias for this function is set_a_equal().
To set two or more process thresholds equal you can use
a2a() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA Dn NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 1 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 0 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------The process thresholds for all processes specified in
names are set equal. The first of the process
names in alphabetical order (here "Dn")
denotes the reference probability that will be estimated. The other(s)
will not be estimated but will be set to be equal to the reference
process threshold. The keep_consts argument can be used, if
you want to keep constants that you already specified and all other
process thresholds should have the same constant, but we suggest to use
a2const() for that.
An alias for this function is set_a_equal().
To hold a process drift-rate constant you can use
nu2const() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 0 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA 1
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 1 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Here, the drift rate for "g" will be set to 1.0 and,
therefore, will not be estimated. You might also use this function with
a vector of names (and a vector of constants).
Note that the new model is not saved because we did not assign it to an
R object.
An alias for this function is set_nu_equal().
To set two or more process drift-rates equal you can use
nu2nu() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 0 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA Dn NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 1 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------The process drift-rates for all processes specified in
names are set equal. The first of the process
names in alphabetical order (here "Dn")
denotes the reference probability that will be estimated. The other(s)
will not be estimated but will be set to be equal to the reference
process drift-rate The keep_consts argument can be used, if
you want to keep constants that you already specified and all other
process drift-rates should have the same constant, but we suggest to use
nu2const() for that.
An alias for this function is set_nus_equal().
To hold a process relative-starting-point constant you can use
omega2const() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 0 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 0 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA NA 0.5
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 1 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------Here, the relative starting point for "g" will be set to
0.5 and, therefore, will not be estimated. You might also use this
function with a vector of names (and a vector of
constants). Note that the new model is not saved because we
did not assign it to an R object.
An alias for this function is set_omega_equal().
To set two or more process relative-starting-points equal you can use
omega2omega() like this:
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Threshold parameters (a):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 means it will be held constant.
## * INFO: 0 of the process thresholds will be held constant.
## -------------------------------
##
## Drift rate parameters (nu):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value between -Inf and Inf means it will be held constant.
## * INFO: 0 of the process drift rates will be held constant.
## -----------------------------------
##
## Relative starting point parameters (omega):
## Dn Do g
## 1 NA Dn NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 1 of the process relative starting points will be held constant.
## -------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 0
## 5 1 2 0
## 4 1 3 0
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 1 distinct delta(s) assumed, namely with mapping [ 0 ].
## -----------------------------------The process relative-starting-points for all processes specified in
names are set equal. The first of the process
names in alphabetical order (here "Dn")
denotes the reference probability that will be estimated. The other(s)
will not be estimated but will be set to be equal to the reference
process threshold. The keep_consts argument can be used, if
you want to keep constants that you already specified and all other
process relative-starting-points should have the same constant, but we
suggest to use omega2const() for that.
An alias for this function is set_omegas_equal().
You can choose which categories of the exponential/diffusion RT-MPT
model should have the same encoding plus motor execution time. Unlike
the processes the motor plus execution times have no names which we can
use to set them equal. Therefore a mapping is used in the function
delta2delta() where the response categories
(categories) can be mapped to encoding plus motor execution
times by using a mapping argument (mappings). Because the
response categories are not always unique the tree (trees)
has to be provided as well.
##
## MODEL OVERVIEW
##
##
## MDL syntax for the MPT part:
## MDL_lines
## 1 # 0 [ 0 , 1 ]
## 2 Do+(1-Do)*g
## 3 (1-Do)*(1-g)
## 4
## 5 # 1 [ 2 , 3 ]
## 6 (1-Dn)*g
## 7 Dn+(1-Dn)*(1-g)
##
## * NOTE 1: Each line in the MDL syntax represents one response category.
## ----------------------------
##
## Process probability parameters (thetas):
## Dn Do g
## 1 NA NA NA
##
## * NOTE 1: NA means the parameter will be estimated.
## * NOTE 2: A value larger than 0 and smaller than 1 means it will be held constant.
## * INFO: 0 of the process probabilities will be held constant.
## -------------------------------
##
## Process completion time parameters (taus):
## Dn Do g
## minus NA NA NA
## plus NA NA NA
##
## * NOTE 1: "minus" refers to the negative outcome (1-P) and "plus" to the positive.
## * NOTE 2: NA means the parameter will be estimated. 0 means it will be suppressed.
## * INFO: 0 of the process completion times will be suppressed.
## -----------------------------------
##
## Mapping of response categories and encoding plus motor execution times (deltas):
## TREE CAT MAP
## 1 0 0 0
## 3 0 1 1
## 5 1 2 0
## 4 1 3 1
##
## * NOTE 1: Unique representation of trees and categories.
## * NOTE 2: Each mapping number corresponds to a distinct encoding plus motor execution time.
## * INFO: 2 distinct delta(s) assumed, namely with mapping [ 0, 1 ].
## -----------------------------------The numbers for the mappings have to start at zero and no whole
number can be skipped. For example in the above code the
mappings cannot be c(2,2) since the number 1
would be missing then in the mappings.
An alias for this function is set_deltas_equal().
The data should be provided with the following variables in this
order: subj, group, tree,
cat, and rt. All of these variables except
rt should have values from zero to the number of unique
values minus one. This will get clear with an example; if we have 60
subjects, two groups, two trees and four categories we would have the
following values in the variables:
subj = {0,1,2,...,58,59},group = {0,1},tree = {0,1}, andcat = {0,1,2,3}.rt should be provided in milliseconds and as integers.
If it has decimal places it will be rounded to a whole number.
Given the right order of the variables and the right values one can
use a data.frame or a path to a text file containing the
variable names in the first line. If not, the
to_ertmpt_data() or to_drtmpt_data() function
can be used to reorder the variables and transform the values of those
variables. Next to the new data.frame the transformation
that is used will be saved in an ertmpt_data or
drtmpt_data list. Note that at least the
variable names should be correctly provided in order to make
to_ertmpt_data() or to_drtmpt_data() work.
These functions are also used automatically in the
fit_ertmpt() or fit_drtmpt() function, but
should be used at least once, when the model is specified the first
time, to check whether the data is transformed according to the
equation/model file.
Here is an example of a data set with unordered variables and wrong values (not starting from zero) and a transformation of this data set:
set.seed(2021)
raw_data <- data.frame(tree = rep(1:2, 8), rt = round(1000*(runif(16)+.3)),
group = rep(1:2, each=8), subj = rep(1:4, each = 4), cat = rep(1:4, 4))
raw_data## tree rt group subj cat
## 1 1 751 1 1 1
## 2 2 1084 1 1 2
## 3 1 1010 1 1 3
## 4 2 682 1 1 4
## 5 1 936 1 2 1
## 6 2 1001 1 2 2
## 7 1 940 1 2 3
## 8 2 567 1 2 4
## 9 1 1115 2 3 1
## 10 2 1283 2 3 2
## 11 1 327 2 3 3
## 12 2 1137 2 3 4
## 13 1 903 2 4 1
## 14 2 867 2 4 2
## 15 1 1120 2 4 3
## 16 2 552 2 4 4##
## DATA TRANSFORMATION OVERVIEW
##
##
## Reordered variables:
## subj, group, tree, cat, rt
## * NOTE1: Additional variables are attached next to these five.
## * NOTE2: To see your data frame use <object name>$data.
## --------------------
##
## Transformed variable(s):
## "subj"
## old new
## 1 1 0
## 2 2 1
## 3 3 2
## 4 4 3
##
## "group"
## old new
## 1 1 0
## 2 2 1
##
## "tree"
## old new
## 1 1 0
## 2 2 1
##
## "cat"
## old new
## 1 1 0
## 2 3 1
## 3 2 2
## 4 4 3
##
## * NOTE: "old" refers to the used labels and "new" to the ones that will be used.
## ------------------------Note that it is never a good idea to specify the tree and category labels/numbers differently from the data file, or vice versa. It is not recommended to define a model with tree and category values starting from zero and using a data set with tree and category values starting from one; Make sure the labels or numbers for these two match.
Finally, with the function fit_ertmpt() or
fit_drtmpt() one can fit the model to the data. This code
should not be run. There are way too few data points.
In this function call we used the default values for all the
parameters that are not listed in the call. model and
data do not have default values. The full call of the
function would look like this:
## do not run
ertmpt_out <- fit_ertmpt(model = restr_2HTM,
data = data,
n.chains = 4,
n.iter = 5000,
n.burnin = 200,
n.thin = 1,
Rhat_max = 1.05,
Irep = 1000,
prior_params = NULL,
indices = FALSE,
save_log_lik = FALSE)
## end not runn.chains is the number of chains with a maximum of 16,
n.iter is the number of samples to draw from the posterior
distribution, n.burnin is analogue to the burn-in phase for
R package rjags and denotes the number of warm-up sampling,
n.thin is the thinning parameter, Rhat_max is
a threshold for the potential scale reduction factor and forces the
sampling to start only when the maximal potential scale reduction factor
of the parameters is lower or equal to this value, Irep is
the number of samples until the next summary is printed,
prior_params is a list of some prior parameter
specifications, indices is a logical parameter with which
one can allow to compute the WAIC and LOO, and save_log_lik
is a logical parameter that allows one to save the log-likelihood for
each posterior sample and data point.
The equivalent for the drtmpt is
Where also the the default values for all the parameters are used.
Also here, model and data do not have default
values. The full call of the function would look like this:
## do not run
drtmpt_out <- fit_drtmpt(model = restr_2HTM,
data = data,
n.chains = 4,
n.iter = 1000,
n.phase1 = 1000,
n.phase1 = 2000,
n.thin = 1,
Rhat_max = 1.05,
Irep = 1000,
prior_params = NULL,
flags = NULL,
control = NULL)
## end not runn.chains, n.iter, n.thin,
Rhat_max, and Irep, are the same as for
fit_ertmpt(). prior_params is still a list of
some prior parameter specifications, but with other prior parameters
than in fit_drtmpt (see section 4 for more details).
n.phase1 and n.phase2 are similar to
n.burnin, but are for the adaptation of the Hamiltonian
algorithm and the estimation of the covariance matrix of all parameters,
respectively. flags should be a list of four logical
variables, namely old_label (the equivalent of the argument
in fit_ertmpt()), indices (also an equivalent
of the argument in fit_ertmpt()), log_lik (the
equivalent of the save_log_lik argument in
fit_ertmpt()), and random_init (which asks
whether the initial value of the MCMC algorithm should be random or
estimated by maximum likelihood). Finaly, control is a list
of numeric variables which gives the user some control over the
algorithm and its speed, namely maxthreads (number of
maximal number of threads for multithreading),
maxtreedepth1_3 (number of tree depth of the no-U-turn
algorithm in phase 1 and 3), and maxtreedepth4 (number of
tree depth of the no-U-turn algorithm in phase 4).
Convergence of the model can be checked by using the fitted object.
Just get the diagnostics and then R-hat. In order to get a traceplot one
can use the traceplot() function from coda.
You can also use the summary() function to get a summary of
the estimates.
Here a code snippet for ertmpt
or drtmpt
In previous versions it was possible to set some restrictions directly in the equation/model file, but due to the number of restrictions that are possible we decided to use now functions instead (see Subsection 1.2).
As we have seen above one can specify an equation file
(eqn_file) like this:
eqn = "
# CORE MODEL
## tree ; cat ; path
0 ; 0 ; Do
0 ; 0 ; (1-Do)*g
0 ; 1 ; (1-Do)*(1-g)
1 ; 3 ; Dn
1 ; 2 ; (1-Dn)*g
1 ; 3 ; (1-Dn)*(1-g)
"The trees, categories, and paths need to be separated by a semi-colon
or a comma, but should not be mixed. As mentioned above the
eqn_file can be provided by a text file through a path to
the file or written directly in R/Rstudio like above.
Another way of specifying the same model is by providing a model file
(mdl_file). This is also not yet the model itself as needed
for the fit_rtmpt() call, but much closer. It is based on
the syntax developed by Singmann and Kellen (2013).
Between two trees (here targets and lures) there must be an empty
line. All paths which lead to the same response category are added
together on one line by a + symbol.
Internally an eqn_file will be converted to an
mdl_file. From that a text file will be written locally
onto your computer (in a temporary file within a temporary folder
created by the R session), used by the fit_ertmpt() or
fit_drtmpt() call, and removed afterwards.
When labels are used in the data set one has to be cautious when
specifying the equation file. The labels of the trees and categories in
the equation file must match those of the data. For example, if the tree
labels “target” and “lure” are used in the data set, one has to use
those also in the equation file (eqn_file). If you specify
a model file (mdl_file) instead of the equation file the
labels in the data set need to be changed to numerics. Otherwise no
mapping between those can be done.
When numbers are used in the data set for the trees and categories it is best to also check that they match with the ones used in the equation / model file, but the program checks for the order. So for example, if you are using the numbers {1, 2, 3, 4} for your four trees in the data set and {0, 1, 2, 3} in the equation file (which is the standard for model files anyway) they will be mapped through the order. The new data, that can be used, will have a zero instead of a one, a one instead of a two, and so on.
One could use labels in the equation file even though you are using numbers in the data file, but it is strongly advised against it. It will be assumed, that the order in which you specify the equations matches the order of the numbers in the data file starting from the lowest to the highest. So if you are using again {1, 2, 3, 4} for the four trees, then the first tree you need to define in the equation file (no matter what label you use) must correspond to tree 1 in the data and so on.
With the function sim_ertmpt_data() (so far no
sim_drtmpt_data() is available) it is possible to generate
data from an exponential RT-MPT model. Required is a model object
generated with the function to_ertmpt_model(), a random
seed number, the number of subjects, the number of trials per tree in
the model, and a named list of parameters. Here it is also possible to
set the mean of mean_of_mu_alpha; A value of zero refers to
the probability of 0.5. If a given probability is desired,
say 0.4, then one might specify
params <- list(mean_of_mu_alpha = qnorm(.4)). If a mean
process time of 200 ms is required, one might specify
params <- list(mean_of_exp_mu_beta = 1000/200). The mean
parameter of the evidence plus motor times is easier to transform, since
they are already on the seconds scale; Just write 500/1000
if your mean encoding plus motor time should be 500 ms. The
code below shows a more or less good balance between too large variances
(leading to too many extreme values like probabilities of zero and one
and RTs of zero) and too small variances (unrealistic data).
Important: If no variances are specified in the params
argument, then the corresponding mean values are fixed, else they will
be randomly drawn.
# randomly drawn group-level mean values
mdl_2HTM <- "
# targets
do+(1-do)*g ; 0
(1-do)*(1-g) ; 1
# lures
(1-dn)*g ; 0
dn+(1-dn)*(1-g) ; 1
# do: detect old; dn: detect new; g: guess
"
model <- to_ertmpt_model(mdl_file = mdl_2HTM)
# random group-level parameters
params <- list(mean_of_mu_alpha = 0,
var_of_mu_alpha = 1, # delete this line to fix mean_of_mu_alpha to 0
mean_of_exp_mu_beta = 10,
var_of_exp_mu_beta = 10, # delete this line to fix mean_of_exp_mu_beta to 10
mean_of_mu_gamma = 0.5,
var_of_mu_gamma = 0.0025, # delete this line to fix mean_of_mu_gamma to 0.5
mean_of_omega_sqr = 0.005,
var_of_omega_sqr = 0.000025, # delete this line to fix mean_of_omega_sqr to 0.005
df_of_sigma_sqr = 10,
sf_of_scale_matrix_SIGMA = 0.1,
sf_of_scale_matrix_GAMMA = 0.01,
prec_epsilon = 10,
add_df_to_invWish = 5)
sim_dat <- sim_ertmpt_data(model, seed = 123, n.subj = 40, n.trials = 30, params = params)
head(sim_dat$data_frame)## subj group tree cat rt
## 1 0 0 0 0 560
## 2 0 0 0 0 456
## 3 0 0 0 0 538
## 4 0 0 0 0 427
## 5 0 0 0 1 420
## 6 0 0 0 0 574With the function fit_ertmpt_SBC() it is possible to
generate data and fit the model to that data using the same priors /
ground truths. The main output of this function will be the rank
statistic for each parameter in the model, which is needed for the
simulation-based calibration (SBC) method by Talts, Betancourt, Simpson,
Vehtari, and Gelman (2018). For example, if this function is repeated,
say 2000 times, with different seeds one might
add all the rank statistics to a matrix (2000 rows and
number of parameters as columns) and then calculate the pearsons’
chi-squared statistic. This allows one to test for how many of the
parameters the rank statistics are not uniformly distributed. A value of
about 0.05 is expected for a test with an alpha level of
0.05.
Here is an example of one replication of the SBC procedure:
mdl_2HTM <- "
# targets
d+(1-d)*g ; 0
(1-d)*(1-g) ; 1
# lures
(1-d)*g ; 0
d+(1-d)*(1-g) ; 1
# d: detect; g: guess
"
model <- to_ertmpt_model(mdl_file = mdl_2HTM)
params <- list(mean_of_exp_mu_beta = 10,
var_of_exp_mu_beta = 10,
mean_of_mu_gamma = 0.5,
var_of_mu_gamma = 0.0025,
mean_of_omega_sqr = 0.005,
var_of_omega_sqr = 0.000025,
df_of_sigma_sqr = 10,
sf_of_scale_matrix_SIGMA = 0.1,
sf_of_scale_matrix_GAMMA = 0.01,
prec_epsilon = 10,
add_df_to_invWish = 5)
SBC_out <- fit_ertmpt_SBC(model, seed = 123, prior_params = params)
SBC_out$ranks
With the following code it would essentially be possible to calculate the rank statistics of each parameter and then test it with the pearsons’ chi-squared test, but much is not considered here (e.g. the convergence and the effective sample size).
# For 2000 replications
## This takes too long to run and in addition, Rhat should always be
## checked as well as the effective sample size.
R = 2000
rank_mat <- data.frame()
for (r in 1:R) {
SBC_out <- fit_ertmpt_SBC(model, seed = r*123, prior_params = params, n.eff_samples = 99)
rank_mat <- rbind(rank_mat, SBC_out$ranks)
}
## pearsons' chi-square for testing uniformity
x <- apply(rank_mat[1:R,], 2, table)
expect <- R/100 # 100 = number of bins/cells (0:99)
pearson <- apply(X = x, MARGIN = 2, FUN = function(x) {sum((x-expect)^2/expect)})
z95 <- qchisq(0.95, 99) # 99 = degrees of freedom
sum(pearson>z95) / length(pearson)With the following code a rank matrix is generated from a uniform distribution and then tested for uniformity:
R <- 2000
rand_rankmat <- matrix(data = sample(0:99, R*393, replace=TRUE), nrow = R, ncol = 393)
## pearsons' chi-square for testing uniformity
x <- apply(rand_rankmat[1:R,], 2, table)
expect <- R/100 # 100 = number of bins/cells (0:99)
pearson <- apply(X = x, MARGIN = 2, FUN = function(x) {sum((x-expect)^2/expect)})
z95 <- qchisq(0.95, 99) # 99 = degrees of freedom
sum(pearson>z95) / length(pearson)## [1] 0.05343511