At a glance
Event Volume Drop (>25% vs baseline) is a Nerve Centre alert tracked from PostHog event data. It fires when total captured event volume falls more than 25% below the trailing 7-day baseline. Because almost everything in PostHog is built on events, a sharp volume drop is usually a tracking failure, a snippet that stopped loading, an autocapture regression, or a blocked SDK, rather than a real collapse in traffic. Treat it as a data-integrity alarm first.
| What it counts | Alert events raised when total event volume falls more than 25% below the 7-day baseline. |
| Sample type | Backend API data from PostHog event counts, evaluated against the alert rule on each refresh. |
| Why it matters | If events stop flowing, every other PostHog card goes blind. This alert protects the data layer the rest of your analytics depends on. |
| Reading the value | A non-zero count means volume dropped past the threshold. Check whether real traffic fell or whether capture broke. |
| Currency | count |
| Time window | RT |
| Alert trigger | total event volume down >25% vs 7D baseline |
| Sentiment key | ph_alert_event_volume_drop |
| Roles | owner, marketing |
Calculation
Calculated automatically from your PostHog data. See the At a glance summary above for what the metric tracks and the worked example below for a typical reading.Worked example
A representative reading of Event Volume Drop (>25% vs baseline) for a typical merchant on PostHog. Suppose your store captures roughly 420,000 events a day. The trailing 7-day baseline is around 420k, so the rule expects at least about 315k. If a deploy on 09 Jun 26 drops the PostHog snippet from the product template and daily volume falls to 240k, the alert fires. Confirm against Total Event Volume and Core Events Firing: if pageviews held but custom events vanished, the break is in your instrumentation, not your traffic. For deeper investigation, use Vortex Mind to trace upstream causes; for natural-language exploration, ask Ask Viq.Sibling cards merchants should reference together
| Card | Why merchants reach for it |
|---|---|
ph_event_volume | Executive sibling: the volume this alert watches. |
ph_core_events_firing | Event Health sibling: are the events that matter still landing. |
ph_alert_tracking_broken | Nerve Centre sibling: a specific core event went silent. |
ph_health_score | Executive sibling: overall tracking health. |
ph_alert_conversion_drop | Nerve Centre sibling: funnel conversion collapse. |
Reconciling against the vendor’s own dashboard
Where to look in PostHog’s own dashboard: Build or open a trend insight on the “All events” series in PostHog and view it daily. The drop below baseline should be obvious. Break the trend down by event name to see whether the loss is concentrated in one event (instrumentation issue) or spread evenly (traffic or SDK issue). Why the Vortex IQ value may legitimately differ:| Reason | Direction | What to do |
|---|---|---|
| Baseline window. Vortex IQ uses a trailing 7-day baseline; PostHog dashboards may compare to a fixed range. | Variable | Match the comparison window. |
| Event filtering. PostHog can exclude internal or test events; Vortex IQ may count differently. | Variable | Align the event filters. |
| Seasonality. A real weekend or holiday dip can cross the threshold legitimately. | Variable | Check whether the drop is recurring and expected. |