Self-fulfilled Prophesy - A participant in a Psychology test may try to be "supportive" by guessing or finding out what the test is all about. Or the tester may be over-zealous in arriving at a preconceived result.
Re-inforcement - A patient may tend to interpret their recollections in such a way that it will comply with psychological terms previously explained to him.
Manipulation - There exist in Society manipulators who may try to manoeuvre people, or those around them, in such a way as to make them think that they are sick in a certain way.
