From experiments
Some contingency tables arise from experiments.
Vitamin C and colds
To test whether vitamin C reduces the risk of catching a cold, a 1961 French study involved 279 skiers over two periods of 5-7 days. Skiers in one group of 139 were given 1 gram ascorbic acid (vitamin C) per day whereas those in the other group were given a tablet that looked similar but had no active ingredient (called a placebo). None of the skiers knew which of the treatments they had received.
Cold | No cold | |
---|---|---|
Ascorbic acid | 17 | 122 |
Placebo | 31 | 109 |
The contingency table above shows the results of the study.
From surveys
Surveys are conducted to ascertain voting intentions, purchases of consumer goods, satisfaction with courses, and for a variety of other research purposes. We will later discuss general principles of data collection from surveys.
Individuals from some target group are usually given a questionnaire to complete. The individual questions are often answered by ticking boxes (e.g. 'Approve', 'Neutral' or 'Disapprove') and are therefore categorical. Some of the resulting categorical variables can often be considered to split the respondents into groups.
Survey data are often reported using many contingency tables.
Contraception and sexual health
The Office for National Statistics in Britain conducts a variety of surveys each year relating to health. The contingency tables below present some results from a survey on contraception and sexual health that was carried out in 2000. There were slightly over 4,200 respondents to the survey.
Age | |||
---|---|---|---|
16-29 | 30-39 | 40-49 | |
Partner sterilised | 6 | 81 | 127 |
Wants to become pregnant | 12 | 28 | 11 |
Pregnant now | 15 | 20 | 2 |
Menopause | 0 | 2 | 11 |
Possibly infertile | 6 | 18 | 19 |
Doesn't like contraception | 3 | 7 | 6 |
Other reason | 15 | 8 | 13 |
Men, aged | ||||||
---|---|---|---|---|---|---|
Sexual partners | 16-19 | 20-24 | 25-29 | 30-34 | 35-39 | 40-44 |
None | 52 | 21 | 13 | 15 | 16 | 18 |
One | 63 | 113 | 147 | 205 | 223 | 211 |
Two or three | 37 | 49 | 28 | 25 | 24 | 18 |
Four or more | 4 | 6 | 2 | 1 | 1 | 0 |
Women, aged | ||||||
---|---|---|---|---|---|---|
Sexual partners | 16-19 | 20-24 | 25-29 | 30-34 | 35-39 | 40-44 |
None | 68 | 10 | 17 | 17 | 26 | 33 |
One | 91 | 145 | 195 | 244 | 290 | 280 |
Two or three | 41 | 37 | 30 | 14 | 10 | 10 |
Four or more | 8 | 12 | 5 | 3 | 3 | 0 |
Marital status | |||
---|---|---|---|
Single | Married or cohabiting |
Widowed, divorced or separated |
|
Family planning clinic (at least once) | 32 | 10 | 3 |
Other | 45 | 34 | 10 |