- Read the paper and answer the following questions with respect to the RCT (40 marks)
a. We are told (page 2) that “We stratified participants by health visitor and randomised in blocks of eight to treatment arms. One member of the research team generated the randomisation schedule by computer, and a researcher who was not part of the research team (blind to any family’s identity) allocated participants.
i. Explain what is meant by stratification (2 marks) and why one might wish to stratify (3 marks).
ii. Explain what is meant by blocked randomisation (2 marks) and why one might wish to employ blocking (4 marks).
iii. Explain what is meant by concealment of allocation (2 marks) and why it is important (3 marks). Comment on the appropriateness of the randomisation process in this study in terms of concealment of allocation (4 marks)
b. We are also told (page 2) that “It was not possible to blind participants because of the type of intervention we used.” Why is blinding desirable in RCTs? (5 marks).
c. The sample size calculation (page 2) indicates that a sample size of 1700 families per arm,
would give “80% power to detect at the 5% significance level a relative reduction of 10% in medically attended injuries between treatment arms”, assuming that “50% of control families would have at least one child having one or more medically attended injuries over the two year follow up period” and allowing for up to 10% loss to follow up.
i. What is meant by a Type 1 error rate (3 marks) and what is the Type 1 error rate for this study (2 marks)?
ii. What is meant by a Type 2 error rate (2 marks) and what is the Type 2 error rate for this study (2 marks)?
iii. Comment critically on the presentation of the sample size calculation in this paper (5 marks).
- Data on the secondary outcome of home safety practices and possession of safety equipment were collected via postal questionnaires from sub-samples of RCT participants. This survey measured possession and use of safety equipment (e.g. smoke alarms, stair gates, window locks) and behavior with respect to storage of potentially hazardous materials (e.g. medicines, cleaning products). A validation check, in the form of a home visit to observe safety equipment and storage practices, was carried out, to validate responses to 26 items in the questionnaire. A random sample of 300 respondents to the postal survey were invited to take part in a “home safety check” and the first 32 respondents in both the intervention and control arms of the trial (64 households in total) were selected to be visited. At the time of the visit, the researcher conducting the home visits was blind to the families’ questionnaire responses, and the families were unaware that the visit was part of a validation exercise.
a. Identify and discuss the implications of three types of biases that might have been observed in the self-reports of possession and use of safety equipment and of storage of potentially hazardous materials (15 marks)
b. Why might there have been disagreements between the self-reports on the questionnaire and the observations at the home visit? (maximum of 10 marks for five factors)
c. The question on window safety catches read “do you have any safety catches on your windows that would stop a child climbing out?” This item showed the poorest match (58% concordance) between self-report and observation. Why might this have been? (5 marks)
- This trial did not include a qualitative component.
a. Briefly explain the value of embedding qualitative research in an RCT. (15 marks)
b. Propose aims and objectives of a qualitative component alongside this particular RCT (15 marks)
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