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In this study 81 experimental and 79 control subjects (randomly assigned to treatments) took Form A of the Nelson Reading Test, twice, with a four week interval between test administrations. Instructions for the retest varied for the E and C groups. The latter group was told that the test was readministered for purposes of assessing improvement. The E subjects were informed that by improving their previous score they would be eligible for winning a prize (candy bars, university sweaters, radios). Analysis of covariance indicated that the effect of the awards was significant (p <. 01) in terms of number of items attempted and in terms of items correct. The adjusted mean increase for the E subjects was three months. The authors concluded that, if the terms of an actual performance contract would be applied to their results, they were to realize approximately 3, 000 profit on a 75 investment.
Tuinman et al. (Fri,) studied this question.