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5.1.3 STEP 3: State the Null Hypothesis and the Research
Hypothesis for the Two-Group t-Test
If you have completed Step 1 above, this step is very easy because the null
hypothesis and the research hypothesis will always be stated in the same way for
the two-group t-test. The null hypothesis states that the population means of the
two groups are equal, while the research hypothesis states that the population
means of the two groups are not equal. In notation format, this becomes:
H o : l 1 ¼ l 2
H 1 : l 1
6¼ l 2
You can now see that this notation is much simpler than having to write out the
names of the two groups in all of your formulas.
5.1.4 STEP 4: Select the Appropriate Statistical Test
Since this chapter deals with the situation in which you have two groups but only
one measurement on each person, plant, or animal in each group, we will use the
two-group t-test throughout this chapter.
5.1.5 STEP 5: Decide on a Decision Rule for the Two-Group t-Test
The decision rule is exactly what it was in the previous chapter (see Sect. 4.1.3 )
when we dealt with the one-group t-test.
(a) If the absolute value of t is less than the critical value of t, accept the null
(b) If the absolute value of t is greater than the critical value of t, reject the null
hypothesis and accept the research hypothesis.
Since you learned how to ﬁnd the absolute value of t in the previous chapter
5.1.6 STEP 6: Calculate the Formula for the Two-Group t-Test
Since we are using two different formulas in this chapter for the two-group t-test
depending on the sample size in the two groups, we will explain how to use those
formulas later in this chapter.
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