Blunden et al. (2011): Behavioural Sleep Treatments and Night-Time Crying (Sleep Medicine Reviews)
The studies cited to defend sleep training do not measure what would settle the question
Sarah Blunden, Thompson and Dawson critique the studies most often cited in support of sleep training. Most are short-term, measure parent-reported outcomes rather than infant outcomes, are not blinded, and use middle-class educated samples that generalize poorly. Sleep Medicine Reviews 15(5):327-334.
Sarah Blunden and colleagues have published several papers, including in Sleep Medicine Reviews, critiquing the methodology behind the studies most often cited in support of sleep training. The critiques focus on several recurring issues.
Most of the studies are short-term, measuring outcomes at six months or earlier, well before any developmental effects would be expected to appear. Most of the studies measure the parent-reported outcome (parents say the baby sleeps better) rather than the infant outcome (the baby's actual sleep quality, stress markers, attachment).
Most studies are not blinded, so the parents and assessors know which intervention is being studied. Most use middle-class educated samples that generalize poorly. The Blunden work has been influential in the academic conversation but has not significantly changed the popular sleep training literature.
Short-term
Typical study window
Parent-reported
Outcome measure
Not blinded
Typical study design
Narrow samples
Generalization concern
Why it matters
The published evidence supposedly showing sleep training is fine does not measure the things that would tell you whether it is fine. It measures whether the parents feel less exhausted, which is not the same question.
This is one finding from the research library behind How to Birth a Mother. Everything here traces back to a study, a dataset, or a systematic review.