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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. | 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?** | **What is the measurement level of scale indices?** |