Workshop Exercise 2: Measures of Effect

February 7, 2024

[10 points]

Please adhere to the "Rules for Collaborating". Submit your workshop through Blackboard.

• Be sure to show your calculations for full credit.
• Express AF and PAF as percentages; round measures of association to 2 decimal places.
• Include units as appropriate.

1. The effect of sleep irregularity on the development of cardiovascular disease (CVD) was investigated in the Multiethnic Study of Atherosclerosis (Huang et al, 2020). Sleep irregularity was measured in terms of the variability (standard deviation, SD) in sleep duration over a 7-day period. Higher sleep duration SD indicates greater sleep irregularity. The data with respect to sleep duration SD in minutes and cardiovascular disease incidence among cohort members, after 6 years of follow-up, are provided in the table.

Sleep duration SD	Person-years at risk	CVD cases
60 minutes	3,278	29
61-90 minutes	2,541	23
91-120 minutes	1,842	26
120 minutes	1,711	33

a) Calculate the rate ratio for the association between sleep duration SD 91 minutes and the incidence of CVD, with sleep duration SD 90 minutes as the comparison group. [1 point]

b) Assuming a causal relationship between sleep duration SD and CVD, calculate the population attributable rate for the effect of sleep duration SD 91 minutes, compared to 90 minutes, on CVD incidence in this population. [1.5 points]

c) Interpret in words the meaning of the population attributable rate that you calculated in part b. [0.5 points]

2) A case-control study was performed among U.S. active duty service members to investigate the development of multiple sclerosis (MS) between 1993 and 2013 (Bjornevik et al, 2022). Below are the results for Epstein-Barr Virus (EBV) seropositivity in the previous 10 years.

	EBV Seropositivity
	Yes	No
Cases	32	1
Controls	51	39

a) Calculate the measure of association for the effect of EBV seropositivity on the incidence of MS. [1 point]

b) Interpret in words the meaning of themeasure of association that you calculated in part a. [0.5 points]

c) Calculate the proportion of MS cases in the study population that were due to being EBV seropositive, assuming a causal relationship between the exposure and the disease. [1.5 points]

3. The following data were reported for the association between sodium intake and inflammatory bowel disease (IBD) in a cohort of adults over a 9-year period, in 21 countries (Narula et al, 2021).

	Sodium intake (g/day)
IBD	3.5	2.5-3.4	0-2.4	Total
Yes	269	73	42	384
No	60,764	11,482	8,402	80,648
Total	61,033	11,555	8,444	81,032

a) Using 0-2.4 g/day of sodium intake as the reference category, calculate the risk ratios for the effect of sodium intake on IBD associated with each of the higher categories of sodium intake [1.5 points]

b) Interpret in words the meaning of the two riskratios that you calculated in part a. [1 point]

4. A cohort study of acute respiratory infections in children 0-2 years old was conducted in a town in Greenland (Koch et al, 2003). The data below were reported for the effect of having smokers in the household on the incidence of episodes of lower respiratory tract infection.

Smokers in household	Child-days at risk	Episodes of lower respiratory tract infection
Yes No	26,812 6,301	255 37
Total	33,113	292

a) Calculate the attributable fraction for the impact of exposure to smokers in the household on the rate of lower respiratory tract infections among children 0-2 years old, assuming a causal relationship between the exposure and the outcome. [1.5 points]

b) Interpret in words the meaning of the attributable fraction you calculated in part a. [0.5 points]