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.

See also, 2D Histograms, Normal Distribution and Bivariate Normal Distribution.