1. An education researcher wants to learn whether it is more effective to put questions before or after introducing a new concept in an elementary school mathematics text. He prepares two text segments that teach the concept, one with motivating questions before and the other with review questions after. He uses each text segment to teach a separate group of children. The researcher compares the scores of the groups on a test over the material.
2. Does stress affect the recall ability of police eyewitnesses? This issue was studied in an experiment that tested eyewitness memory a week after a non-stressful interrogation of a cooperative suspect and a stressful interrogation of an uncooperative and belligerent suspect. The number of details recalled a week after the incident was recorded.
3. Summary statistics for the Eyewitness Accuracy study in Example 2 above are given in the table below. Use a 0.01 significance level to test the claim that stress decreased the amount of recall.
4. In an experiment to study the effect of the spectrum of the ambient light on the growth of plants, researchers assigned tobacco seedlings at random to two groups of eight plants each. The plants were grown in a greenhouse under identical conditions except for lighting. The experimental group was under blue light, the control group under natural light. Here are the data on stem growth in millimeters. Construct a 90% confidence interval for the difference in population means

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