Why might a nonparametric test be useful in testing the hypotheses?  

Otolaryngology, Pediatrics

A common symptom of otitis media in young children is the prolonged presence of fluid in the middle ear, known as middle-ear effusion. The presence of fluid may result in temporary hearing loss and interfere with normal learning skills in the first 2 years of life. One hypothesis is that babies who are breastfed for at least 1 month build up some immunity against the effects of the infection and have less prolonged effusion than do bottle-fed babies. A small study of 24 pairs of babies is set up, in which the babies are matched on a one-to-one basis according to age, sex, socioeconomic status, and type of medications taken. One member of the matched pair is a breastfed baby, and the other member is a bottle-fed baby. The outcome variable is the duration of middle-ear effusion after the first episode of otitis media. The results are given in Table 9.11. 

Table 9.11: Duration of middle-ear effusion in breastfed and bottle-fed babies

 

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Duration of Duration of effusion in breastfed baby (days) effusion in bottle-fed baby (days) Pair number 20 18 11 35 24 182 28 33 58 223 8. 57 39 10 17 76 11 17 186 12 12 29 13 52 39 14 14 15 15 12 21 16 30 28 17 18 15 27 19 65 77 20 10 12 21 22 19 16 23 34 28 24 25 20