An article in the British medical journal Lancet claimed that autism was caused by the measles, mumps, and rubella (MMR) vaccine. This vaccine is typically given to children twice, at about the age of 1 and again at about 4 years of age. The article reports a study of 12 children with autism who had all received the vaccines shortly before developing autism. The article was later retracted by Lancet because the conclusions were not justified by the design of the study.
Explain why Lancet might have felt that the conclusions were not justified by listing potential flaws in the study, as described above.