Epidemiology Help! Efficacy of the Varicella vaccine was tested during an outbre
ID: 166625 • Letter: E
Question
Epidemiology Help!
Efficacy of the Varicella vaccine was tested during an outbreak of Varicella (chicken pox) in a Nebraska town in 2004. Children who were vaccinated and others were monitored during their childhood and cases of chicken pox noted. Data on the number of vaccinated and not-vaccinated and those who acquired Chicken pox are given below. Researchers wish to see if the vaccination program was effective or not? (a) Is the vaccine for varicella effective? Calculate Relative Risk of getting Chicken Pox for this study? Interpret the RR. (b) Calculate and interpret the Odds Ratio (OR). (c) Is the OR similar to the RR? Explain why they are (or not) similar. (d) Calculate the incidence of Chicken Pox in the non-vaccinated that could have been prevented by vaccinations. (AR) (e) What is the proportion of total incidence of Chicken pox in the non-vaccinated that can be attributed to lack of Vaccination? (AR%) Explain your answer.Explanation / Answer
a) Yes the vaccination looks effective the ratio of people who have taken the vaccine and no got the disease is 100/115 is high than those who have not taken the vaccine and not got the disease.
Relative risk=RR=18/27/15/115= 0.67/0.13=5.15
b) Odds ratio=OR
=ad/bc=18*100/9*15=13.31
c)
The relative risk (RR) and the odds ratio (OR) are the two most widely used measures of association in epidemiology. The direct computation of relative risks is feasible if meaningful prevalences or incidences are available.
The probability of an event in the Treatment group is a/(a+b)= R1
the probability of an event in the Control group is c/(c+d) = R2.
The ratio of these two probabilities R1/R2 is the relative risk or risk ratio
RR=(a/a+b)/(c/c+d)
The odds of an event is the number of events / the number of non-events.
If O1 is the odds of event in the Treatment group and O2 is the odds of event in the control group then the odds ratio is O1/O2
OR=a/b/c/d=ad/bc
So odds ratio and relative risk are not similar.
d) Disease Incidence of non vaccinated people, 18 people out of 27 who have not taken the vaccine has got chiken pox.
So the incidence rate= 18/27=0.67 alomost 67%.
Vaccination Disease(Case) No disease(Control) Yes 18(a) 9(b) No 15(c) 100(d)Related Questions
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