Can be defined as the extent to which measures are

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can be defined as the extent to which measures are free from random error, X R . If X R = 0, the measure is perfectly reliable. In test-retest reliability , respondents are administered identical sets of scale items at two different times and the degree of similarity between the two measurements is determined. In alternative-forms reliability , two equivalent forms of the scale are constructed and the same respondents are measured at two different times, with a different form being used each time.
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Reliability Internal consistency reliability determines the extent to which different parts of a summated scale are consistent in what they indicate about the characteristic being measured. In split-half reliability , the items on the scale are divided into two halves and the resulting half scores are correlated. The coefficient alpha , or Cronbach's alpha, is the average of all possible split-half coefficients resulting from different ways of splitting the scale items. This coefficient varies from 0 to 1, and a value of 0.6 or less generally indicates unsatisfactory internal consistency reliability.
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Validity The validity of a scale may be defined as the extent to which differences in observed scale scores reflect true differences among objects on the characteristic being measured, rather than systematic or random error. Perfect validity requires that there be no measurement error (X O = X T , X R = 0, X S = 0). Content validity is a subjective but systematic evaluation of how well the content of a scale represents the measurement task at hand. Criterion validity reflects whether a scale performs as expected in relation to other variables selected (criterion variables) as meaningful criteria.
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Validity Construct validity addresses the question of what construct or characteristic the scale is, in fact, measuring. Construct validity includes convergent, discriminant, and nomological validity. Convergent validity is the extent to which the scale correlates positively with other measures of the same construct. Discriminant validity is the extent to which a measure does not correlate with other constructs from which it is supposed to differ. Nomological validity is the extent to which the scale correlates in theoretically predicted ways with measures of different but related constructs.
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