A vaccine was developed against the Zika virus and its effectiveness tested in a

Question

A vaccine was developed against the Zika virus and its effectiveness tested in a large population of individuals across South America and the Caribbean. The following results were obtained.

Developed Virus

Vaccine Yes: 23 No:1623

Placebo Yes: 99 (A) No: 1584

a. If we assume the vaccine has no effect on Zika infection, how many cases of Zika infection would we expect in the Placebo group (labeled A)?

a. 99

b. 23

c. 61.7

d. 60.3

e. 1621.3

b. What would be the contribution of the Zika infection in the placebo group (labeled A) to the overall x2 test of the independence of Zika vaccine receipt and infection?

a. 22.5

b. ?22.5

c. 61.7

d. 14.1

e. 0.60

No other info given

Explanation / Answer

(A) If we assume the vaccine has no effect on Zika infection, how many cases of Zika infection would we expect in the Placebo group

So here total number of tested people = (23 + 1623 + 99 + 1584) = 3329

Total number of ZIka affected people = 23 + 99 = 122

Total people in placebo group = 99 + 1584 = 1683

Expected number of ZIka affected people in Placebo group = 122* 1683 / 3329 = 61.68

OPtion c is correct.

(b) Here expected table is given below

SO

chi - square statistic

X2 = (99 - 61.68)2/61.68

= 22.58

Option a is correct.

Yes NO Total Vaccine 60.32 1585.68 1646 Placebo 61.68 1621.32 1683 Total 122 3207 3329

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