Procedurally Taxing nicely summarized the National Taxpayer Advocate's new approach to calculating the most litigated issues in her annual report. You can read about her approach starting on page 183 of the report.
Instead of just looking at the tried cases, which she does capture, she also looks at the cases in which taxpayers filed a Tax Court petition. It’s all in how you define litigation. Is it best measured by the relatively small number of cases that get tried and receive an opinion, i.e., looking at the end of the case where about 1% of the filed cases end up, or by looking at the filed cases in which taxpayers started litigation but for a variety of reasons did not follow it to a conclusion by trial and opinion? Since she gives you both sets of data, it’s hard to complain no matter which set of information you prefer.