Select the correct responses Data Table Which of the following is/are true about

ID: 3359530 • Letter: S

Question

Select the correct responses

Data Table

Which of the following is/are true about the table above from a cohort study of PCSK9 mutations in
relation to the incidence of coronary heart disease (CHD)?

a. The incidence of CHD in those with a PCSK9 loss of function mutation is 3.06 per 1000
person-years of observation.

b. The hazard ratio for CHD among those with PCSK9 loss of function mutations is 0.255.

c. PCSK9 loss of function mutation (the exposure) is associated with increased CHD risk.

d. The strength of this relationship tells us that it is causal in nature.

PCSK9 Loss of Function Mutation CHD During Follow-up Person-Years Observation YES 29 9476 NO 116 9654

Explanation / Answer

(a) We are referring to the population with PCSK9 loss of function mutation.

There are total 9476 person-years and among them 29 have incidence of CHD. So incidence rate within this population is 29/9476 = 0.00306 i.e. 3.06 in 1000. So the first statement is exaclty correct.

(b) Hazard ratio is ratio of probability of bveing induced with CHD when having loss of function mutation to probability of being induced with CHD when not having loss of function mutation.

Hence hazard ratio is [29/9476] / [116/9654] = 0.255 (so second statement is also correct)

(c) From part (b) we find that probability of getting induced in CHD when there is loss of function mutation is only around 25.5% of probability of getting induced when there is no lossin function mutation. Hence there is actually reduced risk when there is loss in mutation. So the statement is false.

(d) From a table of association and odds ratio (hazard ratio) we shold never comment on Causal effects. Even if we obtain that there is some direction in the relation, it is better termed as there is some association but we are never sure if that is the cause. There may be many lurking causal variables which affect the association in case observed. So this statement is anyway false.

Also in light of Ans (c), the statement is false as CHD induction does not increase with loss of function mutation.

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Select the correct responses Data Table Which of the following is/are true about

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