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Can you predict achievement from self-control?
Dozens of studies have already established that personality can influence important life outcomes, like getting a good job, staying married, and doing well in school. However, these studies are rarely if ever experimental. As a consequence, hidden variables could be skewing the results.
This study improves the validity of using self-control to predict academic achievement. Although still not experimental, this longitudinal study uses hierarchical linear models (HLM), which can partially rule out the influence of time-invariant hidden variables.
In this four-year study of 189 fifth-graders, increases in self-control were found to predict increases in GPA (r=.18), after controlling for self-esteem, IQ, gender, ethnicity, and income. However, the relationship between average self-control and average GPA was three times stronger (r=.47). That is to say, GPA is moderately influenced by short-term changes in self-control, but a large portion of the difference between high-achieving students and low-achieving students can be explained by the differences in their average levels of self-control.
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Hypothesis: High self-control predicts higher academic achievement; increases in self-control causes increases in academic achievement.
Method: Data was collected from 189 fifth-graders for four years, from fifth to eight grade. HLM growth curve models were used to rule out time-invariant cofounds (an unmeasured variable which does not vary over time).
Measures: Data for each of the measures was collected each year, except for the demographics and IQ data, which was collected just once. A composite self-control measure was constructed through the responses of two informants – parents and classroom teacher, and the self-report of the student, on a self-control questionnaire. Students completed a measure of self-esteem and IQ. The school provided the student's GPA, gender, ethnicity, and family income.
Results: “Changes in self-control during middle school predicted changes in GPA…r=.18.” “Individual differences in mean self-control were associated with individual differences in GPA…r = .47.” “Short-term changes in GPA did not predict subsequent changes in self-control.” “IQ, gender, family income, and ethnicity did not moderate the effect of self-control on GPA.”
Concerns: As the author notes, this longitudinal study is better than a correlation study, but still inferior to an experimental study.
Questions: What factors can explain the difference in the self-control of the children? Why did the mean levels of self-control decrease by 5% from 5th to 8th grade? Does this contradict the maturation of the prefrontal cortex hypothesis?
Duckworth, A. L., Tsukayama, E., & May, H. (2010). Establishing causality using longitudinal hierarchical linear modeling: An illustration predicting achievement from self-control. Social Psychology and Personality Science, 1(4), 311-317.