Evaluating informative hypotheses using bain

I recently presented on Evaluating informative hypotheses for parameters of a structural equation model using Bayes factors at EARA 2020. This blog post was released in tandem with the conference presentation, to provide a brief hands-on tutorial on how to conduct these analyses yourself.

The YouTube video below demonstrates how to evaluate informative hypotheses using bain. If you want to follow along, you can find the full tutorial below. The open access paper detailing these methods is available here (Van Lissa et al., 2020).

If you need to install R before completing this tutorial, I recommend following this tutorial.

Background

A popular theory in psychology to explain social behavior is the Theory of Reasoned Action (TORA, Ajzen & Fishbein, 1980). TORA states that behavior is predicted by behavioral intention, which is in turn predicted by the attitude toward the behavior and the subjective norm about the behavior.

Data

We examine a synthetic data set based on results found by Reinecke, Schmidt, & Ajzen (1996). The behavior under investigation is condom use by 16-24 year adolescents. The dependent variable ‘condom use’ is measured on a 5-point Likert-type scale (How often do you…), and the behavioral intention on a similar 5-point scale (In general do you intend to…). There are three attitude items about condom use (e.g., using a condom is awkward), three normative items (e.g., I think most of my friends would use…), all measured on a 5-point Likert-type scale.

library(foreign)
df <- read.spss("toradata.sav", to.data.frame = TRUE, use.value.labels = FALSE)

Specifying the model

We have 3 indicators for attitude and norm, and observed variables for intention and behavior. We construct a measurement model for the latent variables attitude and norm.

Then, we specify a model based on TORA, with attitude and norms both predicting behavorial intention and behavior.

library(lavaan)
# Model syntax
model <- 'attit =~ attit1 + attit2 + attit3
          norm =~ norm1 + norm2 + norm3

          intent ~ attit + norm 
          behavior ~ intent + attit + norm'
# Estimate the model
fit <- sem(model, data = df)
# Examine model fit
fitmeasures(fit, fit.measures = c("npar", "chisq", "df", "rmsea", "cfi", "tli", "srmr"))
##   npar  chisq     df  rmsea    cfi    tli   srmr 
## 20.000 19.875 16.000  0.031  0.996  0.994  0.025

Examine model results

Let’s plot the model results, so we get an idea of the parameter values.

library(tidySEM)
lo <- get_layout("",       "",       "",       "behavior", "",      "",      "",
                 "",       "",       "",       "intent",   "",      "",      "", 
                 "",       "attit",  "",       "",         "",      "norm",  "", 
                 "attit1", "attit2", "attit3", "",         "norm1", "norm2", "norm3",
                 rows = 4)
graph_sem(fit, layout = lo, angle = 179)

Furthermore, let’s see which parameters are available for bain to specify hypotheses about:

library(bain)
get_estimates(fit, standardize = TRUE)
##   attit=~attit2   attit=~attit3     norm=~norm2     norm=~norm3    intent~attit 
##           0.870          -0.841           0.764           0.725           0.381 
##     intent~norm behavior~intent  behavior~attit   behavior~norm 
##           0.560           0.549           0.156           0.104

Specifying informative hypotheses

The TORA model precludes direct paths between attitude and norm and actual behavior; the effect should be mediated totally by the behavioral intention. Let’s specify two competing hypotheses: One representing the “strict” version of TORA, and one that also includes direct effects from attitudes and norms on behavior. We can refer to the get_estimates() parameters by name.

bain(fit, "(behavior~intent, intent~attit, intent~norm) > 0 &
           (behavior~attit, behavior~norm) = 0;
           (behavior~intent, intent~attit, intent~norm) > 0 &
           (behavior~attit, behavior~norm) > 0")
## Bayesian informative hypothesis testing for an object of class lavaan:
## 
##    Fit   Com   BF.u    BF.c     PMPa  PMPb 
## H1 0.400 0.043 9.318   9.318    0.052 0.052
## H2 0.916 0.005 170.375 2020.119 0.948 0.943
## Hu                                    0.006
## 
## Hypotheses:
##   H1: (behavior~intent,intent~attit,intent~norm)>0&(behavior~attit,behavior~norm)=0
##   H2: (behavior~intent,intent~attit,intent~norm)>0&(behavior~attit,behavior~norm)>0
## 
## Note: BF.u denotes the Bayes factor of the hypothesis at hand versus the unconstrained hypothesis Hu. BF.c denotes the Bayes factor of the hypothesis at hand versus its complement.

Interpretation

The Bayes factors in the column labeled BF.u indicate the ratio of support in favor of the hypothesis, relative to any ordering of parameter values (the unconstrained hypothesis, \(H_u\)). Note that both informative hypotheses, \(H_1\) and \(H_2\), receive more support than the unconstrained hypothesis.

The Bayes factors in the column labeled BF.c indicate the ratio of support in favor of the hypothesis, relative to evidence not in favor of the hypothesis (the complement of the hypothesis, \(H_c\)). Note that both informative hypotheses receive more support than their respective complements; particularly for \(H_2\) the support is overwhelming.

Perhaps most interestingly, we can examine the column labeled PMPb, which contains posterior model probabilities. We can use these probabilities to determine which of a set of hypotheses receives the most support. The unconstrained hypothesis is included in the set as a fail-safe: In case all informative hypotheses are a poor fit for the data, the uninformed hypothesis will receive substantial support. In this case however, we see that \(H_2\) is strongly preferred over \(H_1\) and \(H_u\). Thus, the data cast doubt on the tenet of TORA that there are no direct effects of attitudes and norms on behavior.

Ajzen, I., & Fishbein, M. (1980). Understanding attitudes and predicting social behavior (Vol. 278). Prentice-hall Englewood Cliffs, NJ.

Reinecke, J., Schmidt, P., & Ajzen, I. (1996). Application of the Theory of Planned Behavior to Adolescents’ Condom Use: A Panel Study1. Journal of Applied Social Psychology, 26(9), 749–772. https://doi.org/10.1111/j.1559-1816.1996.tb01128.x

Van Lissa, C. J., Gu, X., Mulder, J., Rosseel, Y., Zundert, C. V., & Hoijtink, H. (2020). Teacher’s Corner: Evaluating Informative Hypotheses Using the Bayes Factor in Structural Equation Models. Structural Equation Modeling: A Multidisciplinary Journal, 0(0), 1–10. https://doi.org/10.1080/10705511.2020.1745644