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Problems and Exercises II
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Interpreting Confidence Intervals for a Comparison Among Several Independent Group Means

A researcher used a single-factor independent groups design to examine children’s eyewitness testimony. There were four different questioning techniques used with four groups of 25 children randomly assigned to the conditions (A,B,C,D). The dependent variable was the accuracy expressed in percentages for reports of a complex scene the children witnessed. Confidence intervals (.95) were drawn around the four means based on the sample data. Results reveal that the intervals for Cond A and Cond C overlap; however, the intervals for B and D do not overlap. Also, intervals for Cond A and C do not overlap with Cond B or D. (You may want to draw this.)

Decide whether the following statements are true or false.



1

The population means represented by Conditions A and C are definitely the same.
2

There is a high likelihood that the population mean in Condition A is different from the population mean represented by Condition C.
3

There is a .95 probability that the population mean for Condition A falls in that interval.
4

The width of the confidence intervals is evidence for the precision with which the population means have been estimated.





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