Decide fi rst whether data are quantitative or qualitative. Unless mentioned oth
ID: 3246839 • Letter: D
Question
Decide fi rst whether data are quantitative or qualitative. Unless mentioned
otherwise, no assumption has been seriously violated, and therefore the appropriate
test should be selected from among t , F , or c 2 tests. Specify the precise
form of the test. For example, specify that the t test is for two population means
with related samples, or that the c 2 test is for two variables, or that the F test is
for repeated measures.
To determine whether speed-reading infl uences reading comprehension,
a researcher obtains two reading comprehension scores for each student
in a group of high school students, once before and once after training in
speed-reading.
Answer: t for two related samples (repeated measures)
Another investigator criticizes the design of the previous study, saying
that high school students should have been randomly assigned to either
the special training condition or a control condition and tested just once
at the end of the study. Subsequently, she conducts this study.
Explanation / Answer
ANSWER TO CASE 1:
t test for related samples (repeated mesures)
EXPLANATION: This is called t test for paired observations. In the usual sample test, the two samples mut be independent, i.e., the values of items in one sample must be independent of the values of the other. But, here, the reading comprehension of the same group of high school students, once before and once after training in speed reading is considered. Here he sample values are not independent. They are correlated pairs.
ANSWER TO CASE 2:
t Test of significance for the difference between two population means
EXPLANATION: Here there are two independent samples: one with special training condition and the other control condition.
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