# PC Labs for SO5041: Week 10

## 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.