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en:general:indices [02.04.2015 17:33] – oezbf2012 | en:general:indices [30.04.2021 09:42] (current) – [Frequently Asked Questions] sophia.schauer | ||
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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' | 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' | ||
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As a rule of thumb Cronbach' | As a rule of thumb Cronbach' | ||
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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?** | ||
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On the other hand, people may answer reversed-polarity items in different ways. For example, someone could avoid to answer " | On the other hand, people may answer reversed-polarity items in different ways. For example, someone could avoid to answer " | ||
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+ | **Mean values or factor values for the scale index?** | ||
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+ | Especially when a scale battery maps several sub-dimensions/ | ||
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+ | The factor scores incorporate the individual items with different weights. | ||
+ | Theoretically, | ||
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+ | Moreover, it should be kept in mind that the concrete factor solution (and thus the weighting) is only one of many possible solutions -- and it is in large part also the result of measurement artifacts, the choice of optimization procedure, etc... | ||
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+ | The lack of comparability and the influence of measurement errors argue for " | ||