How it is measured
For every scored signal and every congressional trade, the clock starts at the first close on or after the filing date, the first price anyone reading the filing could have paid, and not at the insider’s own trade price. Returns are taken at one, three and six months and the benchmark’s return over the same dates is subtracted. A buy that rose 12% while the index rose 10% has an excess return of 2%. A sale is read the other way: the stock falling behind the index is the outcome the sale pointed at.
Prices are adjusted for splits and dividends. Signals without enough price history, for example a company that was delisted, are marked unavailable rather than filled in. Only completed horizons count, so a filing from last month has no six-month figure yet.
Medians, hit rates and sample sizes
InsiderTell reports the median excess return, not the mean, so a handful of stocks that tripled cannot carry a whole group. Next to it is the hit rate, the share of signals whose excess return was positive, and the sample size n. Groups under 30 observations are marked as small. An insider’s track record is the median six-month excess return after their past buys and needs at least three settled buys; a member of Congress’s record is computed the same way after their purchases and, in reverse, after their sales.
Questions
Why measure from the filing date rather than the trade date?
Because the filing date is the first day the public could act on the information. An insider has two business days to file and a member of Congress up to 45 days, so measuring from the trade date would credit a return nobody outside could have earned.
Why the median instead of the average?
Stock returns are skewed: a few large winners pull an average up while most observations sit lower. The median is the middle outcome and describes what a typical signal did. The hit rate and the sample size sit beside it so the spread is not hidden.
What counts as enough data?
InsiderTell marks any group under 30 observations as small and shows the number behind every rate. An individual track record needs three settled buys before a label is given. Past results describe what happened, not what will happen.