Evidence that the researcher used data mining is that he was defensive about the lack of economic theory consistent with his results and that he used the same database of data for all his tests. One way to avoid data mining is to test the trading rule on out-of-sample data.  Sample selection bias occurs when some data is systematically excluded from the analysis, usually because it is not available. Here, the researcher excluded stocks for which he could not determine the CEO’s birthday. Time-period bias can result if the time period is too short or too long. Here, it is likely that the period was too short since the researcher used a cut-off date of the month before the latest market correction. Note: this could be an additional example of data mining.

We are not given enough information to determine if the researcher is guilty of look-ahead bias (which occurs when the analyst uses historical data that was not publicly available at the time being studied).