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
