Increase the length of a test by adding more items. The following techniques can increase the estimated reliability of a test: The last three techniques are employed to assess the internal consistency aspect of reliability. There are several other popular techniques available for measuring reliability. The total variance is the sum of the true variance and the error variance, that is Likewise, the true scores (T j) and the errors of measurement e will have variances F t and V e, respectively. The set of the observed scores has a total variance V o (say). The simplest approach is the so-called variance approach, which makes use of the preceding equation In estimating reliability, one can make use of different sources of variation in measurement values. The correlation must be statistically significant to establish the reliability and the strength of the correlation provides information regarding the dependability of the measures involved. It is usually expected that a coefficient of 0.8 and above implies an acceptable level of reliability. The coefficient varies between ‘0’ (no correlation and therefore, no internal consistency) to ‘1’ (perfect correlation and therefore, complete internal consistency). 
To assess the reliability of any test based on at least interval data, we can use, in general, the Pearson’s product-moment correlation coefficient r, and the resulting correlation will be our estimate of the reliability coefficient. It must always be kept in mind that the reliability refers to a specific measuring instrument applied to a specific population under a specific condition. The third approach to reliability, i.e., the internal consistency, uses only one administration of an instrument or test to assess the consistency or homogeneity among the items. In the 1993 IDD prevalence survey in Bangladesh, for example, eight physicians measured the goiter grade of a single person at a single point of time to assess the extent of error incurred in the measurement due to the physicians. Thus, while stability is concerned with personal and situational fluctuations from one time to another, equivalence is concerned with variations at one point in time among observers and samples of items.Ī good way to assess the equivalence of measurement by different observers is to compare their scoring or evaluating of the same event.
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