# PC Labs for SO5041: Week 11

## Table of Contents

## 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).