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data collection threats

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Name two weaknesses of the following design (i.e, threats to either internal or external validity). Describe how the weaknesses could be overcome.

A. O1 X O2 Two group Pretest- Posttest
O1 -- O2

Note: O = Pretest Observations
O2 = Posttest Observations
X= Treatment
(R) = Random Selection & Assignment to Groups

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Solution Preview

First problem is that the test units are not randomly assigned. See there is no (R) symbol in the symbolic representation of the experiment. Because no random assignment is made the two groups may differ before the treatment and ...

Solution Summary

Data collection threats are discussed in the solution.