The Placebo & The Belief Effect (why positive affirmations are rubbish)

Notes from "Placebo. The Belief Effect" Dylan Evans. Harper Collins Publishers, London. 2003.

There are so many sources of variation in people's responses to placebo, many of which are related to how the recipient processes the information about what is being administered to them and their own levels of skepticism or belief.
If the placebo effect is really 'just' the belief effect, then the magnitude of response should depend on the person's strength of belief in the treatment being administered or experienced. The number of variables that can influence the strength of an individual's belief is virtually unlimited, which leads us to the conclusion that when it comes to placebo responses, only the most vague generalisations can be applied with any certainty...
(p92)

This is further complicated by the fact that people do not always really know what they believe. Just because you want to believe something does not necessarily mean that you do, in the same way that you can say you changed your mind about something but this does by no means guarantee that you have.

There are basically 3 main ways in which we acquire new beliefs:

1. accepting on trust what someone else says, someone who we think is an authority on the matter (for example a trusted doctor or therapist)
2. learning from our own personal experience (I did this before and it worked)
3. logic - to help us figure our previously unrealised consequences or inconsistencies of our old beliefs which cause us to reject them

None of the above are really voluntary - despite convincing illusions to the contrary, we never just decide to change our minds, it changes itself as a result of one or more of the above. Willpower alone does not do it, nor do 'positive affirmations' on their own...but give someone a placebo and you may very well succeed in causing them to acquire the belief needed to boost the immune system which is why placebos are so intimately tied up with the belief effect. Giving a placebo just happens to be a good way of inducing beliefs necessary to trigger various immune mechanisms or neurological responses. Placebos do this via the first and second routes described above.
(p94)