Breastfeeding and risk of childhood asthma: a systematic review and meta-analysis

^#: NOS modifications. 1) Selection: demonstration that outcome of interest was not present at the start of the study; since this is essentially an assessment of temporality of the exposure, but is not particularly applicable to the types of articles we are screening, we changed it to “Does the article assess for breastfeeding at an appropriate time to avoid recall bias (i.e. <2 years of age)?”. 2) Comparability: our three adjusted confounders were family history of asthma or atopy, gestational age and cigarette exposure pre- or post-natally (studies received one star for adjusting for all three, and an additional star for adjusting for other confounders). 3) Outcome (follow-up length): follow-up length is not relevant for the detection of outcome we are looking for; instead we looked at the frequency of follow-up as this is more sensitive for transient asthma diagnoses that may not be chronic; this will be rater-dependent; however, points that will be considered include the total number of follow-ups as well as the timing of the follow-ups (i.e. asthma at 10 years: four well-spaced follow-ups versus three in the first year and one at 10 years). ^¶: NOS conversion to Agency for Healthcare Research and Quality low-, fair- and good-quality scale. Low: <4 NOS stars OR no adjustment for confounders (5 stars) OR nonrepresentative population (1 star) OR major flaw in methodology as determined by assessors; fair: 4–6 NOS stars with adjustment of confounders (5 stars) AND representative sample (1 star) AND an appropriate number of follow-ups conducted for detection of outcome (7 stars); good: >6 NOS stars AND adjustment of confounders with the inclusion of key confounders (5 stars) AND representative sample (1 stars) AND an appropriate number of follow-ups conducted for detection of outcome (7 stars) AND assessment of breastfeeding at a temporally appropriate time to reduce recall bias (4 stars).