Part IV: Managing and Analyzing Data
As you can see, the Regression dialog box offers many options:
Input Y Range The range that contains the dependent variable.
Input X Range One or more ranges that contain independent variables.
Constant Is Zero If selected, forces the regression to have a constant of 0 (which means
that the regression line passes through the origin; when the X values are 0, the predicted Y
value is 0).
Confidence Level The confidence level for the regression.
Residuals The four options in this section of the dialog box enable you to specify
whether to include residuals in the output. Residuals are the differences between observed
and predicted values.
Normal Probability Generates a chart for normal probability plots.
Sampling
The sampling tool generates a random sample from a range of input values. The sampling
tool can help you work with a large database by creating a subset of it.
This procedure has two options: periodic and random. If you choose a periodic sample,
Excel selects every nth value from the Input range, where n equals the period that you
specify. With a random sample, you simply specify the size of the sample you want Excel to
select; every value has an equal probability of being chosen.
T-test
Use the T-test tool to determine whether a statistically significant difference exists between
two small samples. The Analysis ToolPak can perform three types of T-tests:
Paired two-sample for means For paired samples in which you have two observations on
each subject (such as a pretest and a posttest). The samples must be the same size.
Two-sample assuming equal variances For independent rather than paired samples.
Excel assumes equal variances for the two samples.
Two-sample assuming unequal variances For independent rather than paired samples.
Excel assumes unequal variances for the two samples.
Figure 33.10 shows output for the Paired Two Sample for Means T-test. You specify the sig-
nificance level (alpha) and the hypothesized difference between the two means (that is,
the null hypothesis).
