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A HOW TO GUIDE ON THE QUAD MODEL. Thomas J. Allen and Jeffrey W. Sherman Department of Psychology University of California, Davis. Why Do We Model?. Performance on implicit tasks can be influenced by either: Automatic processes OR Controlled processes (Jacoby, 1991)

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a how to guide on the quad model

A HOW TO GUIDE ON THE QUAD MODEL

Thomas J. Allen and Jeffrey W. Sherman

Department of Psychology

University of California, Davis

why do we model
Why Do We Model?
  • Performance on implicit tasks can be influenced by either:
    • Automatic processes OR
    • Controlled processes (Jacoby, 1991)
  • Thus, implicit measures alone cannot tell us if bias is strong b/c of
    • Stronger Associations
    • Weak Cognitive Control OR
    • Both
what do we model
What Do We Model?
  • Association Activation (AC): the degree to which stimuli spontaneously activate attributes
  • Discriminability (D): the degree to which the correct response can be determined
  • Overcoming Bias (OB): the likelihood that D will be selected over AC when D & AC conflict
  • Guessing (G): the likelihood of response bias (e.g. left vs. right key) when D and AC fail
when can we model
When Can We Model?
  • Data can be modeled when the number of categories in an implicit measure exceeds the numbers of parameters estimated
  • That is when there is at least one or more degree(s) of freedom (categories – parameters = df)
when can we model1
When Can We Model?
  • For example, the Implicit Association Test (IAT) has 8 categories:
    • 4 stimuli (Black faces, White faces, pleasant words, unpleasant words)
    • 2 conditions (Compatible trials: When Black & Unpleasant share a key and White and Pleasant share a key versus Incompatible trials: When Black & Pleasant share a key and White & Unpleasant share a key)
what can we model
What Can We Model?
  • With 8 categories, theoretically, we can estimate up to 7 parameters.
  • However, because the equations for 2 of the categories of responses are identical (more on this below), we can only estimate 5 parameters from the IAT:
    • 1 AC for associations between Black and Bad when viewing Black faces or unpleasant words (this parameter biases responses toward the unpleasant key for Black stimuli and the Black key for unpleasant stimuli)
    • 1 AC for associations between White and Good when viewing White faces or pleasant words (this parameter biases responses toward the pleasant key for White stimuli and the White key for pleasant stimuli)
what can we model1
What Can We Model?
  • D for determining the correct response to all 4 types of stimuli
  • OB for determining whether AC or D win out when they conflict (only occurs in incompatible blocks)
  • G for response biases toward the right (pleasant) with G > .50 or left (unpleasant) keys with G < .50
how do we model
How Do We Model?
  • Using the parameters we can construct equations that predict the frequency of correct responses and errors to each of the 8 stimulus categories
  • We can compare these predicted frequencies to the actual frequencies
  • When Chi Squares are non-significant that means there is a good match between predicted and actual values (i.e. model fit)
how do we model1
How Do We Model?
  • Equations for each stimulus category are constructed using a processing tree.
  • The processing tree contains all of the paths that can lead to a correct response or an error
  • Each point in the path is multiplied (i.e. conditional probability)
  • All the different paths are added together to predict the frequencies of correct responses and errors
parameter interpretation
Parameter Interpretation
  • Parameters are probabilities so they are estimated on a scale from zero to one.
  • Values closer to zero can be interpreted as representing less of a process occurring than values closer to one.
  • In equations, a parameter is assumed to either present (AC; D) or absent (1-AC; 1-D)
interpretation of g
Interpretation of G
  • G is usually coded as right key response (or positivity response if the right key is always the ‘pleasant’ key in both compatible and incompatible blocks)
  • 1-G is usually coded as left key response
  • Values below .50 represent response biases in the direction of the left key; values above .50 represent response biases in the direction of the right key
  • Values no different than .50 represent random guessing (no right or left responses biases)
how do we model2
How Do We Model?
  • Example: Black Trials in the Compatible block

Proportion of Correct Response =

ACbb + (1-ACbb)*D + (1-ACbb)*(1-D)*(1-G)

Proportion of Errors = (1-ACbb)*(1-D)*(G)

how do we model3
How Do We Model?
  • Breaking Down the Compatible Black equations:

Correct Proportion

ACbb – Association Activation (Black-Bad) should lead to making a correct response on compatible trials because Black and Bad share the same response key

how do we model4
How Do We Model?
  • Breaking Down the Compatible Black equations:

Correct Proportion

(1-ACbb)*D – When Associations are not activated, but the correct response can be determined (D), the correct response should be made

how do we model5
How Do We Model?
  • Breaking Down the Compatible Black equations:

Correct Proportion

(1-ACbb)*(1-D)*(1-G) – When Associations are not activated AND the correct response cannot be determined, a guess must be made. When that guess is made with the left key (1-G), the correct response will be made.

how do we model6
How Do We Model?
  • Breaking Down the Compatible Black equations:

Error Proportion

(1-ACbb)*(1-D)*(G) – When Associations are not activated AND the correct response cannot be determined, a guess must be made. When that guess is made with the right key (G), an error will be made.

all paths for compatible black

1 - AC

1 - D

1 - G

AC

D

G

Black Face

All Paths for Compatible Black

Compatible

Correct = [AC +

+

(1-AC)*D +

+

(1-AC)(1-D)(1-G)]

+

Error =(1-AC)(1-D)(G)

-

another example
Another Example
  • How would the equations for Black stimuli differ in the Incompatible Block?

Correct Proportion = ACbb*D*OB + (1-ACbb)*D + (1-ACbb)*(1-D)*(G)

Error Proportion = (ACbb)*(D)*(1-OB) + (ACbb)*(1-D) + (1-ACbb)(1-D)(1-G)

another example1
Another Example
  • Breaking Down the Incompatible Black equations:

Correct Proportion

(ACbb)*(D)*(OB) – When Associations are activated (bias toward the unpleasant left key) they conflict with the correct response (right key). Presence (OB) or absence of OB (1-OB) must then determine the response. In this case, presence (OB) favors D over AC.

another example2
Another Example
  • Breaking Down the Incompatible Black equations:

Correct Proportion

(1-ACbb)*(D) – When Associations are not activated (bias toward the unpleasant left key) the correct response can be made if it has been determined.

another example3
Another Example
  • Breaking Down the Incompatible Black equations:

Correct Proportion

(1-ACbb)*(1-D)*(G) – When Associations are not activated (bias toward the unpleasant left key) and the correct response has not been determined, a guess can be made. B/c the Black key is on the right now, a right key (G) guess must be made to get the correct response.

another example4
Another Example
  • Breaking Down the Incompatible Black equations:

Error Proportion

(ACbb)*(D)*(1-OB) – When Associations are activated (bias toward the unpleasant left key) they conflict with the correct response (right key). Presence (OB) or absence of OB (1-OB) must then determine the response. In this case, absence (1-OB) favors AC over D, producing an incorrect response.

another example5
Another Example
  • Breaking Down the Incompatible Black equations:

Correct Proportion

(ACbb)*(1-D) – When Associations are activated (bias toward the unpleasant left key) and the correct response cannot be determined, AC will produce an incorrect response.

another example6
Another Example
  • Breaking Down the Incompatible Black equations:

Correct Proportion

(1-ACbb)*(1-D)*(1-G) – When Associations are not activated (bias toward the unpleasant left key) and the correct response has not been determined, a guess can be made. B/c the Black key is on the right now, a left key (1-G) guess will produce an incorrect response.

all paths for incompatible black

OB

AC

G

1 - OB

1 - AC

1 - D

1 - D

1 - G

D

D

Black Face

All Paths for Incompatible Black

Incompatible

+

-

-

+

+

-

equations
Equations
  • All of the other equations can be viewed on the accompanying model template. Look at the predicted frequencies column
  • On the next slide are all the possible pathways for Black and White stimuli in the compatible and incompatible conditions
what about the attributes
What about the Attributes?
  • In the compatible blocks, the processes that predict correct and incorrect responses for Black and White stimuli are assumed to be the same for Unpleasant and Pleasant stimuli, respectively.
what about the attributes1
What about the Attributes?
  • In older versions of the Quad Model, a separate OB was estimated for Attributes (pleasant and unpleasant stimuli). Often, this parameter was no different from zero (indicating no need for it).
  • Also, theoretically, it makes more sense that individuals attempt to overcome bias on the racial categories rather than the attributes
  • That is, the associations are not bi-directional: Black may activate bad things, but bad things do not activate Black people
what about the attributes2
What about the Attributes?
  • Thus, attributes have the following equations in the incompatible block:

Pleasant correct = (1-ACwg)*D + (1-ACwg)*(1-D)*(G)

Pleasant error = ACwg + (1-ACwg)(1-D)(1-G)

Unpleasant correct = (1-ACbb)*D + (1-ACbb)*(1-D)*(1-G)

Unpleasant error = ACbb + (1-ACbb)(1-D)(G)

using the excel template
Using the Excel Template
  • If the solver is not already under the Tools drop down menu, you can go to Tools, then Add-Ins. Another window will open, then click “Solver Add-In” and then Ok. Excel will then load the program and it should thereafter be visible in the Tools drop down menu.
using the excel template1
Using the Excel Template
  • The Solver add-on in Excel is needed to perform maximum likelihood estimation (MLE) to solve all the equations of the model simultaneously and produce parameter estimates.
  • The solver (using MLE) will attempt to find parameter estimates that minimize the differences between predicted and actual frequencies as much as possible. This will produce the smallest chi square value possible (hopefully non-significant)
using the excel template2

These are the raw correct and incorrect responses that the participants make.

These are the chi-squares that compare the actual and predicted counts.

These are the probabilities estimated by the parameters.

Using the Excel Template
  • First, the raw correct responses and errors need to be calculated for each of the 8 categories and inserted in the Actual Frequency column.
using the excel template3
Using the Excel Template
  • To begin parameter estimation, go to Tools, then Solver. The following window will open:
  • The cells where parameters are located (Column b) are in the changing cell box
using the excel template4
Using the Excel Template
  • To begin parameter estimation, go to Tools, then Solver. The following window will open:
  • In the constraints box, each parameter is constrained to be a value between .000001 and .999999; This can be changed by clicking “change” or additional cells can be included by clicking “add”
using the excel template5
Using the Excel Template
  • To begin parameter estimation, go to Tools, then Solver. The following window will open:
  • In the target cell box, the cell where the overall fit (chi square) will be calculated is selected
using the excel template6
Using the Excel Template
  • The solver will produce parameter values that will produce the smallest possible chi square value (best fit). It is best to initiate the solver 2-3 times to obtain optimal values. The parameters appear in column b:
making comparisons
Making Comparisons
  • After obtaining the initial model fit, parameters in different experimental treatments can be tested for differences
  • To do this, open up the solver and click “add” to put in another constraint
  • Set the parameters you want to compare (e.g. ACbb treatment vs. ACbb control) equal to each other.
  • If the difference between the new chi square value and the old chi square value is significant, then it can inferred that the parameter values for control versus treatment are genuinely different
making comparisons1
Making Comparisons
  • The change in chi square can be tested using 1 degree of freedom on any online chi square calculator.
what stats to report
What Stats to Report?
  • In results sections, the critical numbers to report are the parameter values, overall fit of the model (chi square and p value), and the chi square changes (and their p values) for each parameter comparison
other issues
Other Issues
  • Sometimes, the research question we have requires that we have parameter estimates at the individual level.
  • The previous slides and the template are limited to aggregate comparisons between conditions
  • Individual parameter estimates can be more efficiently calculated using the HMMTree program, which can be downloaded for free at HMMTree
other issues1
Other Issues
  • Model identifiability is another issue that can be addressed by setting the initial parameter values to different values. If the model is identifiable, the solver should settle on the same parameter estimates regardless of the start values.
other issues2
Other Issues
  • When aggregate data is used to estimate parameters and make comparisons, homogeneity of variance is being assumed.
  • This assumption can be tested several ways including using the latent class function on HMMTree. More about latent class analysis can be found in this article, Latent Class modeling using HMMTree
good luck modeling
Good Luck Modeling!
  • Further references

Conrey, Sherman, Gawronski, Hugenberg, and Groom (2005). Separating multiple processes in implicit social cognition: The Quad-Model of implicit task performance. Journal of Personality and Social Psychology, 89, 469-487.

Sherman (2005). Automatic and Controlled components of implicit stereotyping and prejudice. Psychological Science Agenda, 19 (3). link

Sherman (2006). On building a better process model: It’s not only how many, but which ones and by which means. Psychological Inquiry, 17, 173-184.

Sherman, Gawronski, Gonsalkorale, Hugenberg, Allen, and Groom (2008). The self-regulation of automatic associations and behavioral impulses. Psychological Review, 115, 314-335.