Statistical hypothesis testing

Answers

Answers b and d are true; a and c are false.

Statistical hypothesis testing forms the cornerstone of medical and healthcare research. It was used in the above study to establish whether the healing times of leg ulcers differed between community clinics and district nurses. Statistical hypothesis testing started at the position of equipoise—that in the population no difference exists between community clinics and district nurses in leg ulcer healing times over 12 months of follow-up. The aim was to establish whether the sample data supported this position or provided evidence of a difference between treatment groups.

We start by stating the statistical null and alternative hypotheses; this is done before we collect the data. The null hypothesis specifies no difference; for the above study this would be that in the population where the sample was obtained, over 12 months of follow-up the healing times of leg ulcers for patients treated in community clinics are the same as if treated by district nurses (answer b is true and a is false).

The alternative hypothesis states that a difference exists—that in the population where the sample was obtained, over 12 months of follow-up the healing times for patients treated in community clinics are not the same as those treated by district nurses (answer c is false). No direction is specified and the alternative hypothesis is two sided—the healing times for patients treated in community clinics could be shorter or longer than those treated by district nurses.

We use the P value to establish whether the sample data support the null hypothesis or provide evidence of a difference as specified by the alternative hypothesis. The P value is derived using the sample data, and it represents the strength of evidence in support of the null hypothesis (answer d is true). The P value is the topic of next week’s question.