It's not a yes or no answer. Part of what we call "placebo effect" is certainly the result of priming and confirmation bias, but for some specific subjective phenomena (like mood), it is plausible that the effect is real.

>Using "measurement error" as an argument is kind of insulting to the testers as most of them have got to have a grasp of statistics and other factors in order to publish results that aren't going to get them laughed at by the scientific community.

>How do you explain placebo effects in double blind tests?

Being aware of cognitive biases doesn't immunize you to them. There isn't even very good evidence that being aware of cognitive biases reduces your susceptibility to them. There is no shame in that, and any scientist who is insulted by the suggestion that s/he is susceptible to biases should go back to Science School. What being aware of biases does allow you to do is design experiments that compensate for those biases.

And that's the whole reason that we have double blind tests. We know that since humans have to administer and participate in experiments, a lot of biasing factors are going to come into play. So we have come up with designs like that which allow us to measure the extent to which the effects we appear to see are due to biases (or the power of suggestion), and how much the effects can be attributed to an actual effect of the drug.

>Over any period of time, a person will have a great many variations in mood, pain, etc.

>When [...] a subject or researcher has been primed to expect [an effect], the subject or researcher is more likely to notice that effect.

>to this extent, a placebo (or nocebo) effect can be accounted for [by these measurement errors.]

>It is plausible that some specific placebo effects like reduction/increase of pain response, anxiety, and mood could actually be real psychological effects[.]