title: Monitoring Quality of Serverice of all API response time, Which one is better approach median, span 5-95 or upper95?
body: <p>I want to monitor response time of an API. I can methods like average, median and other for monitoring. But I am facing following problems with those methods:</p>
  
  <p><strong>Problem with average</strong></p>
  
  <p>if one of the request taken very high time. For example in given set average will become high due to value 1000.<br>
  S1= [ 1 , 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 1000]</p>
  
  <p><strong>Problem with Median</strong> </p>
  
  <p>It will be correct value only upto 50%. For example in given set S2=[2,2,2,2,2,50,50,50,50]. median gives as value 2 but most of the user are facing slow response. </p>
  
  <p><strong>Problem with 5-95 span</strong> (<a href="http://steveakers.com/2013/08/01/span-vs-median-for-response-time-monitors/" rel="nofollow">http://steveakers.com/2013/08/01/span-vs-median-for-response-time-monitors/</a>)</p>
  
  <p>In above article  author suggested using value uppser95-uppser5. 
  But that will not generate alert if response time is like:
  s3=[50,50,50,50,50] . In this case all API are response are slow. But span 5-95 is zero. </p>
  
  <p>I am thinking of using either of these two values. 
  upper95 or  (upper95+upper5)/2. </p>
  
  <p>Which one will be better and why ? Is there any better method to calculate QOS ?</p>