Normal Fit

The normal/observed histogram represents the most common graphical test of normality. When you select this fit, a normal curve will be overlaid on the frequency distribution. The curve is drawn as a Custom Function (the equation can be reviewed or edited in the User-Defined Function dialog).

The normal function fitted to histograms is defined as:

f(x) = NC * step * normal(x, mean, std.dev.)

The normal function fitted to cumulative histograms is defined as:

f(x) = NC * inormal(x, mean, std.dev.)

where

NC	is the number of cases.
step	is the categorization step size (e.g., the integral categorization step size is 1).
normal	is the normal function.
inormal	is the integral of the normal function.