Over the past couple of weeks, we have offered an analysis of the audit firm market for both larger and smaller public companies. We now turn our attention to the market share for the whole population of US public companies.

Similar to our past analysis, the Big 4 plus BDO and Grant Thornton constitute the top six firms used by public companies for audit work. While not very drastic, there have been some notable changes to the top 10 firms.

McGladrey, which was eighth in the top 10 firms by public company count in 2014, has since rebranded as RSM, and dropped a spot to ninth. Crowe Horwarth, which was tenth, did not make the list this year, having been overtaken by the California-based firm Anton & Chia. Marcum bumped up a spot to eighth place with 1.9 percent of the market, a 36-percent increase from 1.4 percent in 2014.

Altogether, the top 10 firms by SEC company count audited 4,212 of the 6,935 public registrants, or 60.7 percent of the population -- an increase of 3.8 percentage points from 2014.

Not surprisingly, the top six global firms continued to dominate the market of large accelerated filers, auditing 96.8 percent of the 2,005 such companies. The top six also are the top auditors for accelerated filers and non-accelerated filers, with 71.9 percent and 66 percent of each of the respective markets. However, the top six lost some of their market share to other firms compared to 2014, when they commanded 77.4 percent of the market share for accelerated filers and 70.2 percent for non-accelerated filers.

For the market of smaller reporting companies, the top six firms – none of which are one of the Big 4 – hold only 23.2 percent of the market share, leaving the remaining 76.8 percent to be split among hundreds of other firms. Grant Thornton and BDO USA audit more than 2 percent of smaller reporting companies.