Question

A 2016 article in JAMA reports the results of a study of treatment outcomes for children with mild gastroenteritis who were given oral rehydration therapy. Enrolled children were randomized to received either rehydration with diluted apple juice (DAJ), or an electrolyte maintenance solution (EMS). As per the study authors: “The primary outcome was a composite of treatment failure defined by any of the following occurring within 7 days of enrollment: intravenous rehydration, hospitalization, subsequent unscheduled physician encounter, protracted symptoms, crossover, and 3%or more weight loss or significant dehydration at in-person follow-up. Secondary outcomes included intravenous rehydration, hospitalization, and frequency of diarrhea and vomiting.” Of the 323 children randomized to DAJ, 54 experienced treatment failure. (17 %). Of he 324 children randomized to EMS, 81 experienced treatment failure. (25 %)

1. Estimate the risk difference (difference in proportions) of treatment failure for children in the DAJ group compared to children in the EMS group. (DAJ-EMS)

a. 0.08 (8%)

b. -0.08 (-8%)

c. 0.68 (68%)

d. 0.32 (32%)

e. 1.47 ((147%)

f. 0.47 (47%)

2. Interpret the estimated risk difference from question 1 in a sentence.

a. The difference in proportions of treatment failure for children receiving DAJ compared to children receiving EMS is 0.08.

b. The difference in proportions of treatment failure for children receiving DAJ compared to children receiving EMS is - 0.08.

3. Estimate the relative risk (risk ratio) of treatment failure for children in the DAJ group compared to children in the EMS group

a. 0.08 (8%)

b. -0.08 (-8%)

c. 0.68 (68%)

d. 0.32 (32%)

e. 1.47 ((147%)

f. 0.47 (47%)

Answer 1

Answer 1)

Proportions of treatment failure for children in the DAJ group = 17% = 0.17

Proportions of treatment failure for children in the EMS group = 25% = 0.25

Risk difference (DAJ-EMS) = 0.17-0.25 = -0.08 (Option B is correct)

Answer 2)

Interpretation:

The difference in proportions of treatment failure for children receiving DAJ compared to children receiving EMS is - 0.08 (Option B is correct)

Answer 3)

Relative Risk = Proportions of treatment failure for children in the DAJ group/Proportions of treatment failure for children in the EMS group

Relative Risk = 0.17/0.25

Relative Risk = 0.68 (Option C is correct)