Commendable features

1) The QIDS asks about symptoms experienced “for the last seven days”—unlike the longer 2-week period in other depression measures such as the Hamilton, Beck, and the MADRS, and as specified in the DSM-5. The QIDS is therefore more likely to be able to capture an ongoing major depressive episode.

2) Easy to understand verbal-categories answer scales instead of the clinically meaningless numerical rating scales.

De-validating problems

1) The QIDS does not accurately measure the two essential but alternative DSM symptoms of a major depressive episode, MDE, which are severely depressed mood or persistent anhedonia. The QIDS uses “sadness” in place of depressed mood, and for anhedonia it uses “loss of interest” instead of loss of interest and enjoyment, which is the essential feature of anhedonia.

2) It measures the symptoms’ frequency rather than their severity.

3) It fails to record whether the symptoms produce significant dysfunction.

4) It asks about 14 other symptoms that are not essential for depression, and it uses a complex scoring system in which only nine of the 16 items, mostly representing secondary and optional DSM depression symptoms, count toward the total score. This means, for example, that a fairly high score, such as the average 19 out of the maximum of 27 (nine items scored numerically from 0 to 3) reported at baseline in Carhart-Harris et al.’s study, could be obtained with high scores on the optional symptoms and zero or sub-threshold scores on the essential symptoms.