Previous studies have also found that first-borns had an advantage, but these have been criticised for methodological flaws.

Perform enough studies and some are going to produce apparently significant findings because of a small data set, methodological flaws or just through chance.

The review states that interviews were also conducted but this cannot begin to overcome such glaring methodological flaws, particularly given that none of the interviewees has been identified.

However, many of these studies had serious methodological flaws.

Results of trials are usually reported in a briefer academic journal paper, but methodological flaws are often glossed over in the briefer paper.