Home / Event study statistics / Share buyback completed
Share buyback completed
n=3,943as of 2026-07-09
The day a company files that its buyback programme has finished executing.
| Window | Benchmark | n | Mean abnormal return | Median | q value | Significant |
|---|---|---|---|---|---|---|
| Event day | CAR | 2,929 | -0.57% | -0.63% | 0.019 | Yes |
| Event day | BHAR | 2,597 | -0.51% | -0.52% | 0.000 | Yes |
| 5 trading days after | CAR | 2,940 | -1.38% | -1.35% | 0.015 | Yes |
| 5 trading days after | BHAR | 2,608 | -0.63% | -0.96% | 0.000 | Yes |
| 20 trading days after | CAR | 2,927 | -2.65% | -2.07% | 0.076 | Yes |
| 20 trading days after | BHAR | 2,599 | +0.68% | -0.68% | 0.028 | Yes |
| 60 trading days after | CAR | 2,881 | -3.11% | -2.73% | 0.076 | Yes |
| 60 trading days after | BHAR | 2,562 | +2.70% | -0.26% | 0.000 | Yes |
CAR and BHAR point in opposite directions for the 20-day and 60-day windows — both benchmarks are listed as they are; do not read only one of them.
Note: the positive long-window BHAR on buyback events carries a control-group selection effect under our internal review — event firms are matched against same-size firms that never had an event, and that control group itself drifts negative. Under the CAR placebo benchmark the same windows show no excess return. Both benchmarks are shown side by side; do not read BHAR alone as a reason to buy.
Method: the filing's public-availability date is day 0, with a conservative entry on the following trading day. CAR (cumulative abnormal return) is estimated with a market model and calibrated by a placebo test that keeps the event dates but draws random same-day tickers. BHAR (buy-and-hold abnormal return) is measured against size- and liquidity-matched control stocks. All tests carry a multiple-testing correction (BH-FDR). Where the two benchmarks disagree, both are shown as they are — we do not pick the flattering one.
Frequently asked questions
How do Taiwan share prices behave after a company completes a share buyback?
Across n=3,943 historical events measured by this site's event study engine, mean abnormal return -0.57% on the event day (CAR benchmark). Both CAR and BHAR benchmarks are presented, flagged where they disagree. This is not investment advice.
How large is the sample when a company completes a share buyback?
3,943 events, as of 2026-07-09, of which 23 statistical cells clear the significance threshold.
Why do CAR and BHAR disagree when a company completes a share buyback?
The two benchmarks rest on different assumptions: CAR is calibrated with a market model plus a placebo test, while BHAR is measured against size- and liquidity-matched control stocks. Where they point in opposite directions we list both rather than picking the flattering one.
Other event categories
The above is a statistical view of historical events (base rates). It is not investment advice and not a trading signal; a historical distribution does not guarantee the future repeats it. Source: This site's event study engine (computed in-house from official public-source event data; editorial copyright)