This article¹ (you can find the full text on scihub) mentions that many flaws appear in the original study, such as

"Only 6 of the 167 coroner-pronounced SIDS cases used fans, while only 36 of 309 controls used fans."

and

"The case and control groups were not similar at the beginning of the study."

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1: https://pubmed.ncbi.nlm.nih.gov/19414701/