| analysis of variance | See F test.
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| degrees of freedom (df) | A concept used in tests of statistical significance; the number of observations that are free to vary to produce a known outcome.
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| error variance | Random variability in a set of scores that is not the result of the independent variable. Statistically, the variability of each score from its group mean.
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| inferential statistics | Statistics designed to determine whether results based on sample data are generalizable to a population.
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| null hypothesis | The hypothesis, used for statistical purposes, that the variables under investigation are not related in the population, that any observed effect based on sample results is due to random error.
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| power | The probability of correctly rejecting the null hypothesis.
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| probability | The likelihood that a given event (among a specific set of events) will occur.
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| research hypothesis | The hypothesis that the variables under investigation are related in the population, that the observed effect based on sample data is true in the population.
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| statistical significance | Rejection of the null hypothesis when an outcome has a low probability of occurrence (usually .05 or less) if, in fact, the null hypothesis is correct.
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| systematic variance | Variability in a set of scores that is the result of the independent variable; statistically, the variability of each group mean from the grand mean of all subjects.
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| T-test | A statistical significance test used to compare differences between means.
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| type I error | An incorrect decision to reject the null hypothesis when it is true.
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| type II error | An incorrect decision to accept the null hypothesis when it is false.
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