Strength measurements from 41 male students

MVIS (kg)
33
16
35
33
47
40
18
54
18
44
21
29
12
12
26
10
12
20
31
12
19
36
23
22
20
15
15
16
20
13
25
26
41
14
20
22
19
18
23
26
19

Tell students that statistics tries to extract useful information from variation.

Variation that can be understood in terms of other variables is explained variation and is signal.

The remaining unexplained variation is noise (though this natural variation may also be of interest in its own right).

In the first data set (strength of students), all variation is unexplained. No other information about the characteristics of the students is available (e.g. height, weight, age) that might help to explain the variability in the strengths.

The second data set is experimental and the treatment (lathe speed and type of cutting tool) explains most variation in surface finish.

The last data set is observational. Some variation in strength may be explained (understood) in terms of lifetime alcohol consumption.

Student strength

In an ergonomic study involving a group of 41 male students from the University of Hong Kong, each student was asked to exert maximum upward force on a horizontal bar which was close to floor level, with his feet 400mm away from the bar. The force, averaged over a 5-second period, is called the 'maximum voluntary isometric strength' (MVIS) and is recorded in kilograms.

Surface finish from lathe

A mechanical engineer is investigating the surface finish of metal parts produced on a lathe and its relationship to the speed (in RPM) of the lathe. Twenty parts were produced at different lathe speeds and using two different types of cutting tool (code numbers 302 and 416).

Alcoholism and strength

Data that were obtained from 50 alcoholic men who were selected from a larger group of alcoholics to be as similar as possible in age and social characteristics. The researchers estimated the total lifetime alcohol consumption (kg per kg body weight) of each individual and measured the strength of a muscle (kg) in that individual's non-dominant arm.