按月计算标准差

Question

I am trying to calculate standard deviation by month from daily data. I used this function and it's not working (It's returning %DIV/0! ).

{=STDEV.S(IF(AND(MONTH(data!$A$5:$A$3893)=MONTH($I22),YEAR(data!$A$5:$A$3893)=YEAR($I22)),data!H$5:H$3893,0))}

Can you help me about this?

Thanks

Answer 1

The problem is that AND doesn't work well with array formulas. Replace it with a multiplication. Also, remove the 0 in the false part of the if so that it won't ruin your computation:

{=STDEV.S(IF((MONTH(data!$A$5:$A$3893)=MONTH($I22)) *
  (YEAR(data!$A$5:$A$3893)=YEAR($I22)), data!H$5:H$3893))}

Answer 2

The problem is that you can't use the AND operator in an array formula (since it tries to combine all the values into a single true or false).

Also by using 0 as your false value you are introducing false readings. Use a text value instead which stdev.s ignores.

Try {=STDEV.S(IF(MONTH(data!$A$5:$A$3893)=MONTH($I22),if(YEAR(data!$A$5:$A$3893)=YEAR($I22),data!H$5:H$3893,""),""))}

Answer 3

The AND function as used in your formula will combine the month and year tests instead of applying them separately. Use cascading IFs to avoid this. Also, using zero for the case where the IF is false will probably give the wrong standard deviation, because

STDEV.P(1,2,3,0,0,0,0,0) <> STDEV.P (1,2,3). 

Try this:

=STDEV.S(IF(MONTH(data!$A$5:$A$3893)=MONTH($I22),IF(YEAR(data!$A$5:$A$3893)=YEAR($I22),data!H$5:H$3893,"NO"),"NO"))

The "NO" 's in the formula can be any text. When Excel's statistical functions (SUM, AVG, STDEV, etc) encounter a text value, they skip it instead of converting it to zero.

STDEV.P(1,2,3,"NO","NO","NO","NO","NO") == STDEV.P(1,2,3)!!!