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Problems and Exercises I
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Read the following description of psychological research carefully and then answer the questions that follow.

Description:

A developmental psychologist investigates memory performance among second- and sixth- graders as a function of story coherence. Specifically, two types of stories are prepared that are identical except that events in one story are logically ordered according to a theory of memory organization and events in the second type of story are arranged so the natural order of the story is disrupted. The investigator believes younger children will remember less overall than will older children and the logically disrupted story will be harder overall to recall than will the logically ordered story. However, the investigator also predicts an interaction. The investigator believes the effect of the story variable will be less among older children than among younger children. Forty second-graders and 40 sixth-graders are randomly assigned in equal numbers to the two story conditions. Thus, there are 20 children tested in each cell of the complex design. The children are tested individually with the stories presented auditorially using a tape recorder. A trained storyteller makes recordings. Children are asked to recall the story orally when it is completed and retention is scored on at least an interval scale of measurement in a way that we will assume is reliable and valid. Scores can vary from 0 to 100.



1

Answer the following True or False:
  1. The experiment is appropriately described as a 2 X 2 complex design.
  2. One of the independent variables is a natural groups variable.
  3. One of the independent variables is manipulated as repeated measures.
  4. Two main effects are predicted by the experimenter
2

Create a set of hypothetical means that show main effects for each of the independent variables and an interaction as predicted by the experimenter. Construct a design matrix (table) that displays these means.
3

Assume the investigator obtains both main effects and the interaction as predicted; however, also assume that on close examination a critical reviewer of this study suggests that the interaction was due to ceiling effects in the retention scores of the sixth-graders. Construct a design matrix using hypothetical means that shows the predicted results and also suggests that ceiling effects may be responsible for the obtained interaction effect.





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