Internal consistency refers to the general agreement between multiple items (often likert scale items) that make-up a composite score of a survey measurement of a given construct. This agreement is generally measured by the correlation between items.
For example, a survey measure of depression may include many questions that each measure various aspects of depression, such as:
- Loss of interest in activities (X1)
- Negative Mood (X2)
- Weight Loss/Weight Gain (X3)
- Sleep Problems (X4)
- Lethargy (X5)
Assuming the items are worded appropriately and asked of an appropriate sample, we would expect that each of these items would correlate with each of the other items, since they are all indicators depression (see correlation matrix below)...