Does Reddit have an astroturfing problem? What the data suggests

In 51,129 comments from six knife subreddits, the 5% most brand-heavy accounts wrote 11.3% of the brand mentions in buying threads, against 7.9% expected by chance. For one brand it is 31% against 8%. The full Reddit histories of those accounts are 4.5 years old and spread over 66 subreddits, the same as a comparison group, so the data shows concentration and not who paid for it.