What type of study is being described in each of the following situations?

(a) All female patients over the age of 45 on a general practitioner’s list were sent a questionnaire asking whether they had had a cervical smear in the last year.

(b) A group of male patients who had had a myocardial infarction (MI)
were asked about their egg consumption in the previous month. A similar-sized group of males of the same age who had not had an MI were also asked about their egg consumption in the last month, to investigate whether egg consumption was a risk factor for MI.

(c) A secondary school’s records from 50 years previously were used to identify pupils who were active in sport and those who were not. These were traced to the present day, and if they had died, their death certifi cates were obtained to see whether the death rates were different in the two groups.

(d) A new method of removing cataracts (phacoemulsifi cation) has been developed. Eye surgeons are randomised to receive training in the new technique immediately or after one year. The outcome of patients in the two groups is compared in the 6 months following randomisation.

(e) A new centre for chiropractic opens in town. An investigator compares the length of time off work after treatment for patients with back pain who attend the chiropractic centre and those who attend the local hospital physiotherapy centre over the same period.