Page 363 - Statistics for Dummies

Appendix
Tables for Reference
his appendix includes tables for finding probabilities and/or critical
Tvalues for the three distributions used in this book: the Z-distribution
(standard normal), the t-distribution, and the binomial distribution.
The Z-Table
Table A-1 shows less-than-or-equal-to probabilities for the Z-distribution; that
is, p(Z ≤ z) for a given z-value. (See Chapter 9 for calculating z-values for a
normal distribution; see Chapter 11 for calculating z-values for a sampling
distribution.) To use Table A-1, do the following:
1. Determine the z-value for your particular problem.
The z-value should have one leading digit before the decimal point (posi-
tive, negative, or zero) and two digits after the decimal point; for example
z = 1.28, –2.69, or 0.13.
2. Find the row of the table corresponding to the leading digit and first
digit after the decimal point.
For example, if your z-value is 1.28, look in the “1.2” row; if z = –1.28, look
in the “–1.2” row.
3. Find the column corresponding to the second digit after the decimal
point.
For example, if your z-value is 1.28 or –1.28, look in the “.08” column.
4. Intersect the row and column from Steps 2 and 3.

This number is the probability that Z is less than or equal to your
z-value. In other words, you’ve found p(Z ≤ z). For example, if z = 1.28,
you see p(Z ≤ 1.28) = 0.8997. For z = –1.28, you see p(Z ≤ –1.28) = 0.1003.

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