Explain the importance of bias in the context of observational studies and study design. Give two examples of the types of bias that may affect observational studies.

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Assignment questions

1. Explain the importance of bias in the context of observational studies and study design. Give two examples of the types of bias that may affect observational studies.(35)

2. Explain why randomized clinical trials (RCTs) are less likely to be prone to bias compared to observational studies. Describe the key aspects of RCTs which minimise bias.(25)

3. A research team collected data on 25 individuals who had experienced severe knee pain over the last 12 months. Their age distribution was assessed and summarised below.

(a) Describe the type of distribution seen above and explain what type of summary statistics should be used to describe these data correctly.(20)

(b) The research team wished to assess the strength of the correlation between age and knee pain, with pain levels measured on a scale from 0-99 and able to take any value. Explain what analytical approach would be most appropriate and why.(25)

(c) A replication study was repeated 6 months later on a different sample. A scatter plot was produced, correlation analysis conducted and results summarised below:

Explain how you would interpret these findings.(30)

d) What additional information would be helpful to know in order to draw appropriate conclusions?(20)

e) Suppose you had identified three other confounders and collected data on these variables as part of an extended analysis. Assume that the main outcome variable was pain level and age was the main exposure variable. What type of analysis would be appropriate for this example? Explain how you would carry out the analysis.(30)

4. The table below summarises the number of subjects recruited into a case control study examining whether residing in an area with ‘high’ or ‘normal’ levels of air pollution affected the risk of being hospitalised for respiratory illness.

Air pollution Whether hospitalisation was required

Yes (case) No (control) Total

High 44 106 150

Normal 25 120 145

a) Calculate an appropriate estimate in order to compare the probability of being hospitalised in those from a highly polluted area compared to an area with normal levels of pollution. Interpret this estimate(25)

b) What additional analysis might be useful to conduct in order to confirm whether any association between air pollution and respiratory disease was a real causal relationship?(20)

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