Research · 2 min read
The Five-Minute Average That Leaves One in Ten Waiting Twice as Long
Response reporting needs a target-hit rate, upper-tail percentiles, cancellations, and missing arrivals beside the average.
"Average response: 5.6 minutes." Every security proposal carries a number like that — including ours. Here's what ours doesn't say: one in ten arrivals took longer than 10.1 minutes, and one in twenty longer than 12.3. If you plan around the average, the tail will surprise you.
Our analysis of 1,827 dispatches; 1,721 valid recorded arrivals, july 1, 2025 through june 30, 2026.
If the average is 5.6 minutes, what wait should a property plan for?
Among 1,721 valid recorded arrivals from July 1, 2025 through June 30, 2026, half were within five minutes, one in ten took longer than 10.1 minutes, and one in twenty took longer than 12.3 minutes. Plan from the distribution—not the 5.6-minute mean.
The numbers behind the answer
Selected measures only. Denominators and interpretation stay attached so the headline cannot stand alone.
5.0 min
Median valid arrival
Half of 1,721 dispatches with valid recorded arrivals were at or below five minutes.
10.1 min
90th-percentile arrival
One in ten valid arrivals took longer than 10.1 minutes.
36.7%
Arrived within 4 minutes
The complement—63.3%—took longer than the four-minute threshold.
The 5.6-minute average hides a wait twice as long for one in ten arrivals
The mean and median here are close — 5.6 and 5.0 minutes — which makes the average look trustworthy. The tail is where the plan lives. The 90th percentile is 10.1 minutes. The 95th is 12.3. If your property tolerates a six-minute wait, the interesting question isn't the average — it's what share of arrivals beat six minutes, and what the slowest tenth looked like.
That's the fix: report a target-hit rate beside the average. Pick the wait you can tolerate, then ask what percentage made it. Averages can't answer that question. Distributions can.
Planning number
Choose the tolerated wait first, then report the percentage that met it.
A threshold curve shows the experience an average cannot
Read the ladder directly. 36.7% of valid arrivals made it inside four minutes. Half made five. Nine in ten made 10.1 minutes; nineteen in twenty made 12.3. Each rung is a planning decision — the tighter your tolerance, the smaller the share that meets it.
One scope note that matters when comparing providers: this clock starts at dispatch order. It doesn't include the time between the initial alert and the dispatch decision. Anyone quoting arrival times should say where their clock starts.
Evidence visual
Arrival-time percentile ladder
Percentiles use the 1,721 dispatches with valid recorded arrivals. Cancellations and missing arrival times remain outside this distribution and are reported separately.
106 dispatches do not enter the arrival-time distribution
The distribution has a denominator: 1,827 dispatches. 93 were cancelled. 13 never got a valid arrival timestamp. The percentiles come from the remaining 1,721 — 94.2% of the cohort.
Cancellations shouldn't be assigned invented durations — but they shouldn't vanish either. A provider whose average quietly excludes cancelled and missing arrivals is grading their own homework. Keep the excluded rows visible beside the curve.
Define the clock, completion, target, and tail
The defensible scorecard has five parts: what starts and stops the clock; total dispatches with cancelled and missing broken out; the target-hit rate; and the median, P90, and P95. If any piece is missing, the average is doing the hiding.
One more limit: this aggregate combines mobile and posted-on-site response, and it doesn't control for geography, traffic, severity, or concurrent demand. Comparing modes — or explaining the tail — takes separate distributions. Ask for them.
- Clock start and stop definitions
- Total, cancelled, missing, and analyzed cohorts
- Target-hit share
- Median, P90, and P95
- Separate mobile and posted-on-site distributions
Questions property teams ask
Does a 5.6-minute average mean most responses took 5.6 minutes?
No. Half of valid arrivals were within 5.0 minutes, while one in ten took longer than 10.1 minutes.
Why use the 90th percentile?
It describes the slower end directly: 90% were at or below that time and 10% were above it.
Are cancellations counted as slow responses?
No duration is imputed. The 93 cancellations remain visible beside, but outside, the valid-arrival distribution.
Does this prove mobile or posted-on-site response is faster?
No. The current headline combines both modes; comparison requires separate distributions and operating-context controls.
Our methods, limits, and sources
How we calculated this
This is original 911 Sentinel research — we gathered the records, ran every calculation below, and published the aggregate dataset.
We measured minutes from dispatch order to valid recorded arrival across our own dispatches and kept cancellations and missing arrivals outside the duration distribution but inside cohort accounting.
- We validated dispatch order, cancellation status, response mode, and arrival timestamp.
- We separated cancelled, missing, and valid-arrival records.
- We calculated mean, percentiles, and 2/4/6/8/10/12-minute threshold shares.
- We produced response-mode distributions without inferring performance from mode counts alone.
What this analysis cannot establish
- The clock begins at dispatch order, not at the initial alert or acknowledgment.
- Cancelled and missing arrivals are excluded from duration percentiles.
- The aggregate combines mobile and posted-on-site response modes.
- Geography, traffic, severity, staffing, and concurrent demand are not controlled.
- The result describes a cohort and is not a guaranteed response time.
Sources
This study is 911 Sentinel's own work, built from our operational records.
Related questions and practical guides
New coverage — intake open
Ask for the tail before accepting the average
A response plan should define the clock, target, escalation point, cancellation treatment, and upper-tail reporting for the property.