Mood inventories like the PHQ-9 or Kessler are very useful in primary care as patients can appear OK but have very low moods. A single question, The Emoqol 1001, has been developed to enable clinicians to get a quick assessment of their patients' mood.
The question narrative goes like this: "How is your emotional quality of life now, with 100 being perfect and zero being worst imaginable?"
It has a sensitivity of 47% and specificity of 93%. What that means is if their score is 50 or less, the person is very likely to have a PHQ-9 score of ≥ 10, which indicates a low mood. It takes about 15 seconds to ask, is simple and does not require the patient to have their glasses handy.