Question

How strongly do physical characteristics of sisters and brothers correlate? here are data on the heights (in inches) of 11 adult pairs:8?

Answer 1

Answer: moderate (r = 0.516).

These are data on the heights (in inches) of 11 adult pairs, that you forgot to include with your question:



Brother    71  67  66  70  70 71  70  73  72  65  66
Sister      69  64  65  63  65  62  65  64  66  59  62

The strenght of the correlation of two variables can be determined by the correlation coefficient, r.

A perfect positive correlation has r value equal to 1.

A perfect negative correlation has r value equal to - 1.

A correlation coefficient r between 0.7 and 1 shows a strong correlation.

A coefficiaent around 0.5 is moderate, and a coefficient whose absolute value is below 0.3 is weak.

You have to use a graphing calculator, a worksheet program, or a special program to calculate this statistics.

I used Excel and obtained r = 0.516. So, that shows a moderate correlation.

To use Excel' tools to calculate r, follow these steps:

1) Enter the data for brothers is a colum and the data for sisters in the colum next to brother's.

In this way:

Brother Sister
71         69
67         64
66         65
70         63
70         65
71         62
70         65
73         64
72         66
65         59
66         62

2) Select all the data (you may or may not include the name of the variables)

3) Go to the main bar and choose insert

4) Go to the main bar and choose graph, dispersion

That will show the points in a scatterplot.

5) Change to the version of the graph that contains the line joining the dots and the formulas for y and r^2

6) calculate r as the square root of r^2.

I got r^2 = 0.2667, from which r = 0.5164