Diagnosing depression
Depression is thought to be due to an imbalance in the chemical (neurotransmitter) system in the brain. However, when you are suffering from depression, the doctor can't measure this with a blood test or other laboratory method.
The doctor makes a diagnosis depression by asking pertinent questions and by examining you.
Your doctor may ask you to fill out a questionnaire or ‘self-test’ to help him make the diagnosis. For example, in Australia the DASS (Depression Anxiety Severity Score) measures severity of depression, anxiety and stress and comes in the 42 question version or the shorter 21 question version.
The K10 (Kessler Psychological Distress Scale) is another such tool.
Beck's Depression Inventory
Another screening instrument that has been named after the American psychiatrist Aaron Beck, who developed it on the basis of the cognitive psychotherapy model, is Beck's Depression Inventory (BDI). It has been widely used all around the world, where the effect of the cognitive psychotherapy is assessed.
Hamilton's Depression Scale
The British psychiatrist Max Hamilton developed HAM-D, a depression scale, which amongst other things is used by the doctor in an interview with the patient, where he/she asks a number of questions about depression.
Quality of life
Depression affects your daily social functioning. Depression is distinguishable from anxiety for example in the way that it not only affects the persons interest in their daily chores/routines but also the performance of their daily task. This may be due to lack of energy, reduced self-confidence, difficulty concentrating etc.
Quality of life scales have been developed which measure the degree of ‘positive well-being’. One of them is WHO's short five point system, WHO-5, which you can try here.
The WHO-5 questionnaire uses the following scoring: the scale becomes a kind of percentage scale from 0 (worst possible quality of life) to 100 (best possible quality of life). If you score around 50 or less, you should fill out the depression questionnaire, in order to find out whether or not there are signs that point towards depression.