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.

Snail shell temperature

A land snail (Ceaea nemoralis) is more often brown-shelled than yellow-shelled in cooler areas. Pairs of shells were exposed to sunlight at the same time and in the same orientation. Temperatures in degrees Celsius are shown.