A/B Testing Uptime: Control vs Variant Monthly Downtime
Compare control and variant uptime results by monthly downtime, percentage-point change, and practical interpretation.
An uptime comparison can be viewed both as a percentage-point change and as a difference in unavailable minutes. The most useful view depends on whether you are evaluating a short month, a small reliability gain, or a potential regression.
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About A/B Testing Uptime: Control vs Variant Monthly Downtime
An uptime comparison can be viewed both as a percentage-point change and as a difference in unavailable minutes. The most useful view depends on whether you are evaluating a short month, a small reliability gain, or a potential regression.
2
Comparisons
4
Key Factors
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Higher variant uptime versus higher control uptime
Compare the direction of the availability result.
| Factor | Option A: Variant has higher uptime | Option B: Control has higher uptime | What It Means |
|---|---|---|---|
| Estimated downtime difference | Positive downtime saved | Negative downtime saved | The sign identifies which version has lower estimated downtime. |
| Uptime difference | Positive percentage-point change | Negative percentage-point change | The direction follows variant uptime minus control uptime. |
| Availability interpretation | Variant appears more available | Control appears more available | This is based only on the uptime figures entered. |
| Need for supporting metrics | Still needed | Still needed | Latency, error rates, and test quality remain relevant in either case. |
The uptime calculation identifies the lower-downtime version, but it does not explain why the difference occurred or whether it will persist.
Small uptime gap in short and long months
Compare the same availability improvement over different calendar lengths.
| Factor | Option A: 28-day month | Option B: 31-day month | What It Means |
|---|---|---|---|
| Total minutes | 40,320 minutes | 44,640 minutes | A longer month contains more minutes. |
| Downtime difference for the same uptime gap | Smaller minute difference | Larger minute difference | The same downtime rate applies to more minutes in a longer month. |
| Percentage-point difference | Unchanged | Unchanged | Month length does not change the entered uptime percentages. |
| Input selection | Use for February-length periods | Use for 31-day months | Choose the calendar period being modeled. |
Month length changes estimated downtime minutes but does not change the percentage-point uptime difference.
Key Differences at a Glance
Uptime is a percentage, while estimated downtime is expressed in minutes.
A percentage-point gap produces different minute differences in months of different lengths.
Positive downtime saved favors the variant; negative downtime saved favors the control.
The calculation compares availability but does not evaluate performance quality or user impact.
How to Decide
Assumptions
- Control and variant uptime percentages are comparable.
- The selected month is the intended comparison period.
- Downtime is proportionally distributed across the period.
- Availability is the only metric being compared.
Related Comparisons
Frequently Asked Questions
Is a higher uptime percentage always the better option?
For estimated availability, yes, but a complete comparison may also require other performance and experiment metrics.
Why compare downtime minutes as well as uptime percentages?
Minutes translate a rate difference into time unavailable during the chosen month.
Does a 31-day month change uptime percentage points?
No. It only changes the number of minutes represented by the same percentage-point difference.
Can a variant save downtime but still have worse latency?
Yes. Uptime and latency are different measures and should be assessed separately.
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Try the calculator and compare options with your own inputs.