Validity basically means that the test measures what it is supposed to measure. Also, it means that the concept for which the test was developed, and the measurements put in place, are well founded and supported by evidence that justifies the interpretation of the scores.
Reliability means that the results of the test will be consistent. For example, each time a test is administered to any one individual the results should be almost the same. Assuming that the structure and quality of the test is consistent, when the test is given at two different points in time, it will yield similar results. While often confused, validity and reliability are not the same. Validity ensures that the test measures what it has been designed to measure. Conversely, reliability means that the results that are measured are consistent. So, unfortunately, you can have consistency in a test without validity if a test that provides consistent results but is not measuring what is designed to be measuring. This is why both validity and reliability are so important.
The tests must also be scored and administered employing a standard methodology. Research has determined that, if a test is scored and administered in a standard way, the results are more effective and predictable than if they use a non-standard format.
A depression questionnaire or depression test is basically a mood measuring device that gives an indication of emotional and cognitive functioning. Depression tests are developed and designed to evaluate an individuals mood, characteristics, affect and demeanor. Most are also used to track behavior changes over a specific period of time. In most cases, the tests are self administered and they ask you to evaluate your mood or characteristic over the last two weeks or more. Also depression tests that are self administered usually have pre-defined optional responses so there are not free form answers. For example, a test will have the individual choose "a", "b", or "c", or "true" or "false".
A question that is commonly asked is whether the results from a depression test are used to diagnose depression. The answer? In part, yes, the depression questionnaire is used as one reference point to determine if a client is depressed or not. However, it is important to note that there are many other factors that we look at to make a diagnosis. To diagnose depression we need to do a full evaluation by looking at a variety of factors.
Symptomotology is one of the components that are considered. For instance, what symptoms does the client have? How long have they been present? How severe are the symptoms? Has the client experienced these symptoms before? How are they currently functioning emotionally and cognitively? Have they recently experienced any traumatic events? Also, is the client currently using drugs or alcohol? If so, how often do they use?
The mental health history of the client is considered as well - have they been diagnosed with depression before? What about the family history? Has any of the client's family members been diagnosed with depression?
It is also important to rule out any other medical conditions that might cause or contribute to the depressed feelings. Is the client suffering with another condition such as Lymes disease, Rheumatoid Arthritis, Chronic Fatigue Syndrome, a hypothyroid condition, and any nutritional deficiencies? All of these things, and many others, need to be carefully considered before making a formal depression diagnosis.
A depression questionnaire and depression tests are available on-line. However, if want reliable results it is important to take one that is professionally developed (ie. not by a Webmaster!). This will ensure that the depression test meets the Standards for Education and Psychological Testing. What this ultimately means is that it will be valid - testing for signs of depression like it is supposed to, and that the results you get will be reliable and statistically relevant.
It would be horrible to take a depression questionnaire that generates incorrect results. It can tell you that you're depressed when you really aren't or tell you that you aren't depressed when you really are. In either case, you will be misled and will not proceed in a matter that would be in your best interest. If you take a depression test that meets the aforementioned criterion, you can rely on the results and determine the best course of action.