NORMDIST function in excel giving values greater than 1

**excelwho** · 08-11-2008, 06:41 PM

Hi,

I'm using the normdist function with 'false' argument to generate a probability density function: NORMDIST(0.04,0,0.3,FALSE) is giving a value greater than 1 which can't be correct since this function is supposed to return a probability. Has anyone seen this before?

thanks

**seckert** · 08-13-2008, 02:13 PM

When using the "false" option, divide the result by 100.

**shg** · 08-13-2008, 04:06 PM

When using the "false" option, divide the result by 100.

That's not even wrong.

NORMDIST(x, mean, dev, FALSE) does not return a probability; it returns the density function, which is the slope of the cumulative distribution function. For a continuous variable, the probability of any particular value is zero, because there are an infinite number of values.

If you want to know the probability that a continuous random variable with a normal distribution falls in the range of a to b, use

= NORMDIST(b, mean, dev, TRUE) - NORMDIST(a, mean, dev, TRUE)

The peak value of the density function occurs at the mean (i.e., =NORMDIST(mean, mean, dev, FALSE) ), and the value is

=1 / (SQRT(2 * PI()) * dev)

The peak value will exceed 1 when the deviation is less than 1 / sqrt(2pi) ~ 0.399.