How to calculate standard deviation based on the avergae formula

[#1]

Hi,

I have a bar chart , and this is my expression in the chart

Expression : COUNT(if([SLA_DAYS_PAST]<=0,[PPL_ID]))/COUNT(if([SLA_FLAG]=-1,[PPL_ID]))  (sl_flag_past<=0 indicates compaints that are taken care of on or before due dates) and (sla_flag=-1 indicates all the closed complaints)

Calculated Dimension : if(CLOSE_DATE>=vMinDate, MonthName(CLOSE_DATE))

Now, first of all I need to build an SPC CHART, so I have calculated the average value using this expression:

Average: COUNT(TOTAL <PPL_ID> if([SLA_DAYS_PAST]<=0,[PLL_ID]))/COUNT(TOTAL<PPL_ID> if([SLA_FLAG]=-1,[PPL_ID]))

Now to calculate upper and lower control limits, i need to get the standard deviation:

uppercontrol_limit : average+STDEV

lower control_limit=average=STDEV

So, I need a formula to find the STDEV. I have a dead line, and i really appreciate your time.

-Sarayu

[Gysbert_Wassenaar]

Use the stdev function. See the help file for details.

[#3]

Hi ,

Thank you for your time. I knew about the STDEV function we have, but the problem is how to use it with my above expression. Please let me know if you have worked on this before or any idea about this.

[Gysbert_Wassenaar]

I have no idea. I don't understand how your 'average' expression can calculate the average of anything. I don't know what the 'anything' is, so I don't know how to calculate the stdev of it.