From previous histograms including those of height and birthwt, you may have noticed that a number of variables have distributions which may be described as symmetrical about their mean and bell shaped. It would be useful if these distributions could be described empirically (a numerical equation of a curve which approximates well to the symmetrical bell shape so often seen). A good approximation to many such variables is given by the normal distribution. This has a rather ungainly equation of:
where 
= the mean and 
=
the standard deviation of the distribution being modeled.
In Figure 23, a line showing equation of the
Normal distribution with
= 3263.23 and
= 553.52 approximating the distribution of birthwt is shown.
Introduction
|
Summary
Statistics |
Descriptive Statistics
|
Sampling | Normal Distribution
| The t-Student Distribution
|
Correlation and Regression
|
Analysis of Variance
|
Contingency Tables |
Non-Parametric Statistics
