Reporting Response Times - Percentile Distributions and Trends

Response time metrics can be very misleading.  An average of 2 seconds can mask occasional very high values that could be relevant to performance goals.  It can also mask cyclical trends.  The same is true of reporting median or specific percentiles such as 95th percentile.  An informative response time report should include two elements:

1. Response time percentile distribution
2. Response time trends with enough granularity to see spikes and patterns

Here is an example of these two elements:

Response Time Percentile Distribution

The distribution chart shows clearly what percentage of response times might be above the response time goal.

Response Time Trend

The trend chart shows clearly an upward trend over time, an important property that would be lost in any single response time metric.  It also includes enough granularity to show the distribution pattern of response time spikes.