5.3.3. Log-Probability Histogram

The program will first compute the number of observations falling within each class as in the case of ordinary frequency histogram. Then cumulative percentages are computed at the upper limit of each class interval and these percentages are plotted on a normal-probability Y-axis (probit scale) against the logarithm of the upper class limits on the X-axis.

If the frequency distribution of data is log-normal, then the points should lie on a straight line. A drop-down list is provided to connect X-Y points with straight lines or to draw a line of best fit on them.