I was looking at the formula to compute a standard deviation using sum and sum of squares (without having to know the mean in advance.)
Using udb 7.1.0, I tried the formula, comparing it to what the stddev function returned, and noticed a different answer. I varied the formula to do a final divide by (n) rather than by (n - 1) and then got the same answer as udb. Could this be a problem with the stddev function? My query ran: with raw ( x ) as ( select dec(week_seq,17,5) from hc.t_week ) select sqrt((sum(x*x) - ((sum(x)*sum(x))/count(*)))/( count(*) - 1 )) as "right" , sqrt((sum(x*x) - ((sum(x)*sum(x))/count(*)))/ count(*) ) as "wrong" , stddev(x) as "db2" from raw ; And the results were: right wrong db2 ------------------------ ------------------------ ------------------------ +1.28027340829996E+002 +1.27882758806651E+002 +1.27882758806651E+002 -- Eldon Tucker ===== To unsubscribe, send 'unsubscribe' to [EMAIL PROTECTED] For other info (and scripts), see http://people.mn.mediaone.net/scottrmcleod
