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.