# PC Labs for SO5041: Week 11

## Week 11 Lab: Correlation

### 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?

### 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.

### Linear Regression

Do `sysuse nlsw88` to load the National Longitudinal Study of Women data set that comes with Stata. Look at `wage`, the hourly wage rate. Predict `wage` using `grade`:

`reg wage grade`

Write out the `Y = a + bx` equation. Calculate the predicted value for `grade=0` and `grade=20`, and draw the line on a graph (on paper).