The following 2 x 2 table represents a study of exposure X and disease Y relatin
ID: 3224675 • Letter: T
Question
The following 2 x 2 table represents a study of exposure X and disease Y relating to your provided disaster scenario. Using the data in the table below, calculate the appropriate ratio measure of association for your chosen study design in Part 1 (in other words, calculate either the odds ratio or the risk ratio). Interpret the result in terms of the exposure you selected in Part 1 and a health endpoint plausibly related to this exposure.
Diseased
Not Diseased
Exposed
65
120
185
Not Exposed
20
135
155
85
255
Odds ratio:
Risk ratio:
Interpretation:
Diseased
Not Diseased
Exposed
65
120
185
Not Exposed
20
135
155
85
255
Explanation / Answer
The Table can be rewritten as follows
65
a
120
b
20
c
135
d
The Odds Ratio (OR) = (a/c) / (b/d) = (65/20)/(120/135) = 0.2735
Odds Ratio Interpretation; What do the Results mean?
Here our odds ratio is less than 1. This means that Exposure to the causes of disease has a lower probabilty of the individual actually contracting the disease.
The Risk Ratio: = (CIe) / (CIu), i.e., the ratio of the cumulative incidences in the exposed and unexposed groups.
Therefore the Risk Ratio (Diseased)= (CIe) / (CIu) = 35.135/12.90 = 2.723
and Risk Ratio (Not Diseased)= (CIe) / (CIu) =64.865/87.097 = 0.745
Interpretation:
Risk Ratio(Diseased) : In this study patients who were exposed had 2.723 times the risk of contracting the disease compared to patients who were not exposed to the disease. Basically the probabily of contracting a disease when exposed is higher when not being exposed.
Risk Ratio (Not Diseased) : The interpretation here is that those who were no exposed to the causes of the disease had 0.745 the times the risk of contracting compared to those who were exposed to the disease.
A note: The Odds ratio gives us the range (higher/lower/equal) probababilities of getting a disease when exposed to the cause.
The Risk ratio takes into account that you got the disease, then how much times would the risk be when exposed to the causes against not being exposed to the causes.
Diseased Not Diseased Total Exposed65
a
120
b
185 Not Exposed20
c
135
d
155 Total 85 255 340