Blood pressure and the pill

  Blood pressure  
Subject Before pill After pill Difference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
70
80
72
76
76
76
72
78
82
64
74
92
74
68
84
68
72
62
70
58
66
68
52
64
72
74
60
74
72
74
-2
-8
-10
-6
-18
-10
-4
-26
-18
8
0
-32
0
4
-10

Is the mean of the differences zero?


Use the examples on this page to introduce the idea of paired data. Explain that we can answer questions about whether the means of the two variables are the same by analysing the differences (as a univariate data set).

Blood pressure and the pill

Does the pill affect blood pressure? The blood pressures of 15 college-aged women were recorded before they started the pill and after using it for 6 months.

Environment and IQ of identical twins

Identical twins are genetically the same, so any differences are caused by their environment (or experimental treatment for animals). The table below shows the IQs of ten pairs of twins who were raised apart — one in a 'good' environment and the other in a 'poor' environment.

Repair estimates from two garages

An insurance company is concerned that garage A is charging too much for repairing damage to cars. Ten damaged cars were taken to both garage A and another garage for estimates.