Cohort Study on Physical Activity and CHD, Case-Control Study on Dietary Fat and Skin Cancer, Bias in Cohort and Case-Control Studies

University
Task
ASSIGNMENT 2
Date

Based on the research article
Question 1
(a) The type of study portrayed by the above article is (1 mark)
- This is a cohort study which entails following the certain group of persons of
interest for a certain period of time to assess exposure outcomes on a longitudinal
study.
(b) Data used to obtain the first study participants entailed [2 marks]
- The study utilized data from the Swedish Annual Level of Living Survey, which
details a national representative of the non-institutionalized population. This
sample obtained included 7090 women and men between ages 35-74 surveyed
between 1988 and 1989.
(c) The authors excluded a total of 1984 participants from the study because [2 marks]
- They rated their general health as poor hence this was for a reason to remove
underlying conditions which might affect the assessment of coronary heart
disease. As these factors could have a confounding effect on the focus of the
study.
(d) The crude overall incidence for CHD was [2 marks]
- The crude incidence rate was 59 cases per 10,000 persons over the various levels
of physical activity.
(e) Comparison of relative risks and physical activity levels [4 marks]
- The physical activity engagement of twice a week had RR of 0.72 at CI between
0.52-1.01 compared to low-income earners having RR of 1.20 at CI interval of
0.95-1.52 compared to those of other incomes at RR at 1.
(f) The relative risks discussed above can be best explained through [3 marks]
- Physical activity engagement of twice a week led to a reduced incidence rate of
coronary disease exposure.
- The low-income earners were linked to increased risks of exposure towards
getting coronary heart disease while other income category earners had no effect
on the emergence of the disease.
(g) Relative risks in this study are better described as [2 marks]
- The relative risks in this task can be described as risk ratio, as it outlines the
probability of developing coronary heart disease on exposure to physical activity
compared to those not engaging in intense physical activity and at the same time
level of income as a risk factor of developing coronary heart disease.
(h) The major confounding factors which were not considered in this study which could
have a significant factor on the study results include; [4 marks]

- The major confounders which were not considered in this study include disease
and social factors such as hypertension, smoking, obesity, and
hypercholesterolemia.
- These factors have the opportunity to progress the development of coronary heart
disease as they are major underlying factors and risks factors for CHD
development. However the researchers omitted the participations who had poorly
rated health state, the above factors could be within the recruited participants.
- These risk factors thus signify profound confounding factors which were not
litigated in the study. Thus physical activity could not be extensively be assessed
with regard to the development of physical; activity among the participants.
(i) Why do you think the author could not adjust for these confounders? Hint: think
about the way this study was designed [4 marks]
- The authors of this study could not confound the factors mentioned above due to
the study framework in that it excluded the participants who rated their self-
health as poor. This could mean that people who were obese, overweight,
smoking and even having other factors such as diabetes were excluded from
participating in the study.
- Further, as the study was prospective in nature, the participants could have
developed these conditions as the study was progressing. As mentioned and
outline during the study, these assessments were not undertaken hence could
mean that the respondents could have been having underlying health issues which
coupes up to be coronary heart disease being a final factor and cause of death.
Question 2:
A case-control study on the intake of dietary fat and the development of skin cancer
Comparison groups in the study involved
Cancer cases =500
Case-control subjects= 500
Dietary intake cases
Low consumption intake = 150
High consumption intake = 80
Control
Low consumption intake = 130
High consumption intake cases 100
a) Data summary table for disease state and fat intake [4 points]
Having disease Without the disease Total
High fat intake 80 100 180
Moderate fat
intake
270 270 540
Low fat intake 150 130 280
Total 500 500 1000