Chi-square test and Pearson’s r correlation

1. You are interested in determining whether offenders who are labeled as ‘psychopaths’ are more likely to be assessed as ‘high risk’ on the SIR-RI. Pleased use the variables of psychopath and RiskCat to address the following questions.

a) Using JASP, create a 2  2 contingency table containing these variables.
a. Which category has the highest frequency?
b. Calculate, by hand, the expected frequencies for each category. Show your work.
b) Using JASP, conduct a chi-square test to examine the relationship between psychopathy and risk category (i.e., psychopath and RiskCat).
a. Report the chi-square value and whether the frequencies are significantly different from what you would expect by chance.
b. Write-up the results in an APA-style blurb (refer to Lecture 5 for how to write-up the results of a chi-square test).

2. You want to examine the relationship between risk and sensation seeking (SSStotal), therefore, you decide to fit a linear model to your observed data on these variables to examine whether a linear relationship exists between an offender’s risk classification and whether they are sensation seekers. Please address the following questions using the variables risk and SSStotal.

a) Using JASP, calculate the means & standard deviations for the two variables.
b) Using JASP, create histograms for both distributions.
a. Does the sample for risk appear normally distributed?
b. Does the sample for SSStotal appear normally distributed?
c. Does normality of the samples matter here? Briefly explain why or why not.
c) Using JASP, create a scatterplot (called correlation table in JASP).
a. Do the variables appear linearly related? Briefly describe why or why not.
b. Does the assumption of homoscedasticity appear to be upheld? Briefly describe why or why not.

d) Using JASP, compute a Pearson’s r correlation between the two variables (risk and SSStotal).
a. Report the Pearson’s correlation between the two variables and whether it is significantly different from .00.
b. Write-up the results in an APA-style blurb (refer to Lecture 5 for how to write-up the results of a correlation).