Genetic and Environmental Modifiers of Hereditary Haemochromatosis - Engineering Assignment Help

Assignment Task :

Question 1  

The presence of iron-deficient anaemia (IDA) was recorded for pre-menopausal (aged < 45 years old) and post-menopausal women (aged > 55 years old) participating in the “HealthIron” cohort study of the genetic and environmental modifiers of hereditary haemochromatosis (inherited iron-overload disease). Out of all the pre-menopausal women, 213 women were found to have IDA and 513 women did not have IDA. Of the post-menopausal women, 199 women were found to have IDA while 1158 women did not have IDA. 

a) Calculate and interpret:

(i) the risk difference,

(ii) the risk ratio, and

(iii) the odds ratio for the association between menopause and iron-deficient anaemia. 

b) Calculate and interpret the 95% confidence interval for:

(i) the risk difference,

(ii) the risk ratio, and

(iii) the odds ratio. 

c) Use the estimated odds ratio and the standard error of the odds ratio to calculate and interpret the p-value for the null hypothesis of no association between menopause and iron- deficient anaemia. 

Question 2 

As part of a research program to study the association between alcohol consumption and the risk of iron overload disease among middle-aged Australians, a sample of 188 participants in the Melbourne Collaborative Cohort Study were recruited in a pilot study. Of these 188 participants, biochemical analysis of blood samples revealed that 43 had elevated serum iron. 

a) Calculate and interpret a 90% confidence interval for the population proportion of middle-aged Australians with elevated serum iron based on the data from this pilot study. 

b) Calculate the sample size required for a larger study that aims to obtain an estimate of the population proportion of middle-aged Australians with elevated serum iron with a precision of ± 3% (i.e., half the width of the 95% confidence interval is 3%). For an initial estimate of the population proportion, use the value calculated in part (a) for the pilot study described above. 

c) The study investigators believe that the estimate of the population proportion of middle-aged Australians who have elevated serum iron calculated from the pilot study is inaccurate. They believe that the true population proportion of middle-aged Australians with elevated serum iron could lie anywhere between 10% and 50%. What sample size would you now recommend for a larger study that aims to obtain an estimate of the population proportion of middle-aged Australians with elevated serum iron with a precision of ± 3%?

Question 3

A randomised controlled trial comparing progesterone versus placebo in patients with a severe head injury is said to have 80% power to detect a 10% absolute reduction in the risk of death (risk difference = 0.10) with a type I error rate of 5%. 

a) What is the probability that this trial would fail to detect a true risk difference of 10% units? Explain how you have reached your answer. 

b) How could you change aspects of the experimental design (power, type I error rate, sample size) so that the probability of failing to detect a true risk difference of 10% units is reduced? What information required for a power-based sample size calculation is not given above? 

Question 4

A randomised controlled trial was conducted to compare nicotine replacement gum versus placebo for stopping smoking. All participants were smokers at the beginning of the study. The primary outcome measure was stopping smoking for six months or more. The researchers reported the following: 

“A significantly higher proportion of smokers who received nicotine gum stopped smoking during the 6 months of follow-up compared with the placebo group (p-value <0.05)”. 

a)  What information is not provided by the researchers in the above statement? 

b) Is stating p<0.05 sufficient? Please explain. 

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