The basic listing of the number of mergers and sizes of acquired companies was obtained from the FTC overall merger series. This series was found to contain many errors: Some mergers appeared more than once, some mergers were reported that did not occur. The “histories” of each acquiring company as reported in Moody's Industrial Manual were used as a check against the FTC data to determine the year of acquisition, size of acquisition, and whether they did actually occur. The assets reported in the FTC Large Merger Series were substituted for those in the Overall Series whenever the two differed. When an acquired company was itself listed in Mi>Moody's, its assets in the year prior to its acquisition were used if no other figure was available.

For those mergers for which no assets figure for the acquired firm was reported, but the amount of cash or stock exchanged for the acquired company was reported, a consideration paid figure was used as the value of the assets acquired. In general, the consideration paid exceeds the book value of assets acquired. On a stock exchange acquisition, the consideration paid was computed at the midpoint of the stock's price range in the year of the merger.

When it was known that the assets of an acquired firm were subsequently sold – for example, following an antitrust decision – the acquisition was not recorded.