Monday, August 20, 2012

Using Percentiles for Statistical Purposes

Sometimes when I am running Load Tests or general reports, I need to use percentiles to know how what the "feeling" is overall instead of just the average. This is important for things like how long it takes for a page to load, the duration of database queries, etc.

Here are a few simple percentiles to consider that I use often:

P10 Avg - (StdDev * 1.645)
P35 Avg - StdDev
P90 Avg + (StdDev * 1.645)
P95 Avg + (StdDev * 1.96)

Avg = Average (Mean would be even better). It does take into account that your data has a normal distribution.