PUBH5010 Epidemiology Methods and Uses Essay Sample

Assignment: PUBH5010 Epidemiology Methods and Uses
Name
University
Course Number and Name
Tutor’s Name
Date
Section A
Professor Merdemy studied risk factors for shoulder injury. He conducted a study to assess whether swimmers were more likely to sustain a shoulder injury compared to weightlifters. The study had 1,800 participants – 700 swimmers and 1,100 weightlifters. Both groups were followed for 12 months and there was no loss to follow-up. During follow-up, any participant with a new episode of shoulder pain had an ultrasound of the painful shoulder and a radiologist confirmed whether there was a new injury to the shoulder. Of the 1,100 weightlifters, 58 had a new shoulder injury during the study. Of the 700 swimmers, 39 developed a new shoulder injury during the study. Doing push-ups was suspected of increasing the risk of shoulder injury. Dr Merdemy was concerned that this might interfere with the study results because he knew doing push-ups was a common activity for swimmers and weightlifters. Of the swimmers, 200 reported regularly doing push-ups and 15 of these swimmers developed a new shoulder injury during the study. Of the weightlifters, 800 reported regularly doing push-ups and 47 of these weightlifters developed a new shoulder injury during the study.
Solutions
1 Calculate the crude relative risk of developing a new shoulder injury in swimmers compared to weightlifters. To do this you will need to draw a 2*2 table.
* Show this table. (5 marks)
2 x 2 table

Developed new shoulder injury?


Yes

No

Total

Swimmers

39

661

700

Weightlifters

47

1042

1100


97

1703

1800

* Show your working. (5 marks).
Risk for shoulder injury among swimmers = 39/700
Risk for shoulder injury among weightfighters = 58/1100
Risk ration = Risk for shoulder injury among swimmers Risk for shoulder injury among weightfighters
Risk ration = (39/700)/ (58/1100)
Risk Ratio = 0.055710.05272
Crude Risk ration = 1.05671
2 Interpret the result you obtained (in Question 1) in words that someone who has not studied epidemiology would understand. (5 marks)
The risk ratio (RR) is 1.05671 which is closer to one, meaning that the outcome is similar in both groups (swimmers and weight fighter). In simple terms, there is no significant difference between the two arms of the study in relation to developing shoulder injury after exercising.
3 Do you think regularly doing push-ups has confounded the estimate of whether swimmers are more likely to develop a new shoulder injury than weightlifters? Justify your answer, both in terms of the relative risk estimates and the criteria for confounding. Show any relevant working. Assume for the purposes of this question that doing push-ups is NOT on the causal pathway between the type of athlete (swimmer or weightlifter) and developing a new shoulder injury. (20 marks)
The crude risk ration is simply the risk of shoulder injury from swimming/ the risk of shoulder injury from weightlifting = 1.05671
Calculating Risk ratio for shoulder injury among push up players:

Developed new shoulder injury?


Yes

No

Total

Swimmers (push-up)

15

185

200

Weightlifters (push-up)

47

753

800


62

938

1000

Risk ration = Risk for shoulder injury among push-up swimmers Risk for shoulder injury among push-up weightfighters
Risk ration = (15/200)/ (47/800)
Risk Ratio = 0.0750.05875
Risk ratio = 1.2766
The crude risk ratio is less than the stratified risk ratio, which means that the crude risk ratio is confounded by performing press-ups.
4 Is there evidence of effect modification? Explain your answer in one or two sentences and show any relevant working. (4 marks)
When effect modification exists, there will be different results for different levels of the third variable. Using data from the 2 x 2 table.
Participants

Developed new shoulder injury after push-ups?


Yes

NO

Total

Swimmers

15

185

200

Weightlifters

47

753

800


62

938

1000

Odd ratio (OR2) after pushups = (15 x 753)/ (185 x47)
= 1.299022

Developed new shoulder injury?


Yes

No

Total

Swimmers

39

661

700

Weightlifters

47

1042

1100


97

1703

1800

Odd ration (OR1) using without pushups = (39 x1042)/(661x47)
= 1.308076
OR2 is slightly higher than OR1 meaning that effect modification exists but extremely lower. This means that push-ups as a third variable have a slight effect on swimmers and weight builders’ risk towards shoulder injury.
5 What proportion of swimmers who do push-ups develop a new shoulder injury because they are swimmers rather than weightlifters? (2 marks)
Proportion = 200 (15/200) + 800 (47/800)
= 62/200
=31%
6 How many people who do push-ups would have to change from being weightlifters to swimmers for ten extra people to develop new shoulder injuries (4 marks)?
800 weightlifters = 47 cases of shoulder injury
2...