Vitamin C and colds

One group of 139 skiers was given 1 gram ascorbic acid (vitamin C) per day and another group of 140 was given a placebo. Which skiers got colds?

     Cold      No cold  
Ascorbic acid 17 122
Placebo 31 109

Explain that contingency tables can arise from:

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.
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.
This table gives the main reason for not using contraception by the 410 women aged 16-49 who were in a sexual relationship, not using contraception and not sterilised.