KB36924: Standard deviation metric does not return correct values in MicroStrategy 10.x

SYMPTOM:
 
Standard deviation metric does not return correct values in Strategy 10.x
 
STEPS TO REPRODUCE:
 
Follow the steps below to reproduce the issue using Strategy tutorial project:

• Create a standard deviation metric (SD) with metric definition "Stdev(Profit) {~, Month}". This is to apply standard deviation function on the out-of -the-box Profit metric and set the metric level to <Report Level> and <Month, Grouping None>.
• Create a report with attribute Region, Year, Month, and metric Profit, SD (the metric created at Step #1).
• Execute the report, notice that SD returns the same value for every month, as shown below:
  

CAUSE:
 
The behavior is working as designed.
 
When calculating metric SD, SQL engine will first calculate its inner metric Profit, which is at report level, so here data is already aggregated to Month level. The value returned is actually the standard deviation value of a whole year's Profit data.
 
ACTION:
 
Define the correct metric level for the inner metric Profit. To get the standard deviation value for each month, the inner metric should be able to return values at Day level.
 
Inner Metric shoule be Sum(Profit) {~, Day}, as shown below:

 
For the SD metric, set its level to report level (Stdev() {~}), as shown below:

 
 
After applying the modification above, correct data is returned, as shown below:

 
NOTE: For best practice, always define metric level for the inner metric, because engine aggregates the inner metric before applying the outer function and the inner metric level affects the selection of base fact table used for aggregation.