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--- en:general:indices [02.04.2015 17:33] – oezbf2012
+++ en:general:indices [02.04.2015 17:34] – [Frequently Asked Questions] oezbf2012
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 The calculation of a scale index is only sensible if all items reflect the same construct. In practice you can test this by computing the correlation between the items by means of Cronbach's alpha.
 As a rule of thumb Cronbach's alpha should be above .7. However, Cronbach's alpha is highly influenced by the amount of items. Therefore a scale with only 4 or 5 items can be plausible with an alpha value of .6.
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 Yes and no. In principle the size of the correlation is independent from the number of items. However, in a neatly constructed scale the quality of the measurement is increased by the number of items. Therefore the scale index contains fewer measurement errors and as a result higher correlations may be observed.
-To the contrary a correlation based on more items can actually be overrated if both constructs underlie the same measurement error. The higher correlation with more items is a spurious correlation in this case – e.g. because some people prefer to answer on the right end of the scale (acquiescence).
+On the contrary a correlation based on more items can actually be overrated if both constructs underlie the same measurement error. The higher correlation with more items is a spurious correlation in this case – e.g. because some people prefer to answer on the right end of the scale (acquiescence).
 **What is the measurement level of scale indices?**