Chip Concentration — computed from official holder-distribution data, open formula
"Chip concentration" is one of the most-quoted, least-computed phrases in Taiwan retail investing. We compute it directly from the official weekly holder-distribution filings: an HHI concentration index, mega-holder (1,000+ lot) ratios with weekly deltas, and retail-share changes — every number traceable to the source brackets, with open deterministic formulas.
How it is computed
The official filing buckets shareholders into 15 lot-size brackets. We compute the HHI (sum of squared bracket shares) — the standard academic concentration measure — plus mega-holder ratios and weekly deltas. Every row carries its availability-date stamp: filings settle Friday and publish the following week, so backtest signals only activate after publication.
Rising concentration is not a buy signal
An increase in the mega-holder ratio can mean accumulation, but it can equally come from convertible-bond conversion, a buyback, or a bracket shift after an ex-dividend adjustment. The filing shows the redistribution, never the motive.
The indicator answers how much concentration changed. It does not answer why it changed or whether to act on it.