PC Labs for SO5041: Week 10

Table of Contents

1 Week 10 Lab: Independent sample t-test, correlation

1.1 Hypothesis testing exam marks

Say that in last year's Leaving Cert English exam, the average mark achieved was 62.1%. A year later, the Dept of Education wants quick feedback on whether the standard has changed. A random sample of 100 scripts are assessed and marked. Their average mark is 65.2% with a standard deviation of 12.4%

Conduct a test of the hypothesis that the standard has changed, using a 95% level of confidence. Report and interpret your findings.

1.2 Independent Sample t-test in Stata

Load the following file, which contains information on gender and work hours for a UK sample (use http://teaching.sociology.ul.ie/so5041/labs/week11a). Use summaries and graphs to get a sense of the male-female differences, and then use an independent sample t-test (i.e., ttest varname, by(groupvar), replacing varname and groupvar with the names of the appropriate variables).

1.3 Correlation

The following data file contains six pairs of variables, X1 and Y1, X2 and Y2 etc.

use http://teaching.sociology.ul.ie/so5041/labs/correl

First, graph all six pairs in scatterplots. Also graph X1 with Y2. What sort of association do you see in each case (positive, negative, none, strong, weak)? Make a guess what the value of the correlation coefficient might be (write it down).

For each graph, get the correlation coefficient: e.g., corr x1 y1. How do the reported correlation coefficients correspond with those you guessed?

1.4 Correlations with real data

With the following data file (use http://teaching.sociology.ul.ie/so5041/ocorr), explore the correlations between the variables it contains, graphically and with the correlation coefficient.