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# Calculating Standard Deviation and Mean: Include zeros?

Posted on 2010-11-11

A sample of 30 items were pulled from a universe of 323.

Each of the 30 rows has an "overpayment" amount. Values range from $0 to $7,000.

16 of 30 rows have an overpayment value > zero.

14 of 30 rows have an "overpayment" value = zero.

I need to calculate the Mean and Standard Deviation of the overpayment amount.

Are rows with a value of zero used in this calculation?

[My calculations done two different ways:]

Mean ($65,235.42 / 30 total items including zeros) $2,174.51

Mean Overpayment ($65,235.42 / 16 overpayments) $4,077.21

Standard Deviation (of 16 overpayments) 1546.38

Standard Deviation (of all 30 rows including $0 "overpayments") 2348.83