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Volume Anomaly Detection

Z-score based detection of unusual trading volume on the NZX — spikes, clusters, and price-volume divergences (last 30 days)

130

Total Anomalies

Volume Spikes

Volume Clusters

Divergences

Pre-Announcement

Why Volume Anomalies Matter on the NZX

The NZX is a relatively thin market — average daily turnover across all stocks is approximately $100-200M. This means even modest institutional flows can create detectable volume anomalies. A spike that might be noise on the NYSE could indicate meaningful activity on the NZX. Volume anomalies flagged here preceded a material announcement within 5 trading days in 45% of cases (58 of 130 anomalies).

Anomalies by Sector

Sector	Anomalies	Spikes	Clusters	Divergences	Pre-Announcement
Industrials	29	17	7	5	14
Financials	24	8	9	7	17
Consumer Discretionary	20	11	6	3	5

Recent Volume Anomalies

130 anomalies detected across 59 tickers in the last 30 days (z-score ≥ 2).

Ticker	Company	Date	Volume	vs Avg	Z-Score	Price Chg	Type	Severity	Ann.
WHS	The Warehouse Group Limited	2026-08-13	694,386	8.7x	5.0	+4.55%	Volume Spike	extreme	-
WHS

Methodology

This tool uses statistical z-score analysis on daily OHLCV data to identify three types of unusual volume activity. It does not imply wrongdoing — unusual volume may result from index rebalancing, block trades, research coverage changes, or simple market interest.

Volume Spikes

Single-day volume z-score exceeds the threshold (default: 2.0) against a 50-day rolling mean/stdev. A z-score of 2.0 means volume is 2 standard deviations above the 50-day average — statistically unusual (occurs ~2.3% of the time in a normal distribution).

Volume Clusters

3 or more days within a 7-day window where volume exceeds 2x the 50-day average. Sustained elevated volume may indicate ongoing accumulation or distribution by institutional investors, or building market interest ahead of an event.

Price-Volume Divergence

Volume exceeds 2x the 50-day average but price moves less than 1%. This pattern may indicate accumulation (buying absorbed by selling) or distribution (selling absorbed by buying). In thin NZX stocks, it can also indicate block crosses at the prevailing price.

See also: Whale Tracker — large insider transactions. · Coordinated Trading — clustered insider activity. · Insider-Announcement Correlation — timing analysis. · Technical Signals — trend and momentum indicators.

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Predicted HY/FY reporting dates for all NZX companies based on historical patterns.

Data sourced from NZX stock price and volume data, NZX company announcements. Our datasets may not be complete. Automated analysis can produce errors. Past performance does not indicate future results. If you believe any data on this page is incorrect, please contact us at hello@nzxplorer.co.nz.

For informational purposes only. Not investment advice.