What is the difference between feeling sad and feeling unhappy? The first two questions on the Burns Depression Checklist ask about (1) Feeling Sad and (2) Feeling Unhappy. Specifically, they ask how much you have experienced:


Feeling sad or down in the dumps
Feeling unhappy or blue


What is the difference between these two questions?

References


The BDC is from the book Feeling Good, by David Burns.
It is common for psychological tests to include multiple items with similar meaning. These items are then combined to form an overall scale score (e.g., depression or depressed thoughts). Multiple items with a similar meaning are used to increase the reliability of measurement, which is also important for validity.

I don't think there is a huge difference in meaning between the two items, and presumably they are highly correlated. However, they may provide slightly different connotations to different people. Thus, by having multiple items, the scale may have improved reliability.