Area Below Negative Z
(A worked Problem:  Procedure explained in more detail in Chapter 7)

Suppose that a personality test has:

Mean = 200
Standard Deviation = 50

What is the proportion of people taking this test that score below 175?

I.  First you must convert the original score to a Z score.

II.  Because the Z score is negative and we want to find the area below then:

    A.  We can find the pink shaded area in Column 3 of Table Z

            Z = -.50

            Column 3 Value = .3085

    B.  The area above a +Z score is just the Column 3 value = .3085 or 30.85%

Copyright © 2004 by Mark W. Vernoy