4 ms·

One really important point about the placebo effect that a lot of people miss is that a lot of it is not a real physiological change caused by the placebo, but

One really important point about the placebo effect that a lot of people miss is that a lot of it is not a real physiological change caused by the placebo, but is a result of bias in both the subject and the experimenter. Over any period of time, a person will have a great many variations in mood, pain, etc. (which a subject is able to self-examine), and a great many variations of biological function (which a researcher is able to measure). When those variations correspond to effects that a subject or researcher has been primed to expect, the subject or researcher is more likely to notice that effect. This is simple confirmation bias. If you think trained scientists couldn't possibly stumble on that kind of pitfall, you should read about N-rays[1]. This is just as likely to be true for the "nocebo" effect as for the placebo effect. Dizziness, for example, is a very common symptom for people to experience for myriad benign reasons. Orthostatic hypotension (head rush) is a common cause of dizziness, and it is affected by a lot of minor factors like hydration, vasodilation, how long you've been sedentary, how fast you stand up, etc. This may happen to you three times in a week, and you'd never pay it any mind. But if a doctor told you that a medicine you were taking might cause dizziness, you would notice it. So to this extent, a placebo (or nocebo) effect can be accounted for with absolutely no "mind over matter" style physiological change whatsoever. It is plausible that some specific placebo effects like reduction/increase of pain response, anxiety, and mood could actually be real psychological effects involving suggestion. But if you hear of a placebo doing something and you think "how could a belief in a placebo possibly have that kind of effect", it's very likely that you are at least partly seeing mere measurement error. [1] http://en.wikipedia.org/wiki/N-rays http://en.wikipedia.org/wiki/N-rays

sp332 14y ago
That's interesting but I'm sure it doesn't explain everything. For example pain is actually experienced differently (confirmed by watching nerve pathways light up on fMRI scans) depending on people's expectations. http://www.ninds.nih.gov/news_and_events/news_articles/news_article_pain_perception.htm http://www.ninds.nih.gov/news_and_events/news_articles/news_...
- mistercow 14y ago
  I did actually cover that in my last paragraph. There are certain effects that are known to be highly subjective and therefore it is not implausible that a real effect from placebos could be seen, even accounting for biases.
  - gnaritas 14y ago
    Don't you just hate it when you head off obvious counter arguments and someone comes along and makes it anyway!
SeanDav 14y ago
Not sure I get what you are trying to say here. Are you saying placebo/nocebo effects are real or not? 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?
- pessimizer 14y ago
  If those are the only two possible answers that you'll accept, he's not saying anything you will hear. >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[.]
- mistercow 14y ago
  >Are you saying placebo/nocebo effects are real or not? 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.
TheComedian 14y ago
Though I understand that you aren't denying the placebo effect, I'm confused about why you feel that a large amount of the placebo effect is due to bias. After all, most drug trials are double-blinded and placebo controlled, so surely in these trials the placebo effect is legitimate (assuming no scientific fraud).
- Haplo 14y ago
  The placebo is actually there in double-blinded tests to remove any bias and other factors related to the experiment. And no matter how good/legitimate the experiment, any measurement pretty much always causes changes. The actual effect of the placebo is usually at most a small portion of all the factors that are measured by it. Of course this depends heavily on the experiment in question and some drugs (like psychological ones) have a higher placebo effect than others. A lot of people seem to have the idea that the placebo effect is very big for medication outside of experiments - but most of the time it's very small to non-existing.
  - Semaphor 14y ago
    Considering the placebo effect (unless you think bioresonance therapy is true) cured me of several allergies, I'm pretty happy with how strong it is:)
    - mistercow 14y ago
      Or your allergies just went away as you got older, and you attribute that to the placebo effect.
      - pygy_ 14y ago
        There are complex interactions between the nervous and immune systems. I don't think that anything has been demonstrated regarding allergies, but I wouldn't rule out a therapeutic effect in this case. The absence of evidence is not an evidence of absence.

sp332 14y ago

That's interesting but I'm sure it doesn't explain everything. For example pain is actually experienced differently (confirmed by watching nerve pathways light up on fMRI scans) depending on people's expectations. http://www.ninds.nih.gov/news_and_events/news_articles/news_article_pain_perception.htm http://www.ninds.nih.gov/news_and_events/news_articles/news_...

mistercow 14y ago
I did actually cover that in my last paragraph. There are certain effects that are known to be highly subjective and therefore it is not implausible that a real effect from placebos could be seen, even accounting for biases.
- gnaritas 14y ago
  Don't you just hate it when you head off obvious counter arguments and someone comes along and makes it anyway!

SeanDav 14y ago

Not sure I get what you are trying to say here. Are you saying placebo/nocebo effects are real or not? 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?

pessimizer 14y ago
If those are the only two possible answers that you'll accept, he's not saying anything you will hear. >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[.]
mistercow 14y ago
>Are you saying placebo/nocebo effects are real or not? 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.

TheComedian 14y ago

Though I understand that you aren't denying the placebo effect, I'm confused about why you feel that a large amount of the placebo effect is due to bias. After all, most drug trials are double-blinded and placebo controlled, so surely in these trials the placebo effect is legitimate (assuming no scientific fraud).

Haplo 14y ago
The placebo is actually there in double-blinded tests to remove any bias and other factors related to the experiment. And no matter how good/legitimate the experiment, any measurement pretty much always causes changes. The actual effect of the placebo is usually at most a small portion of all the factors that are measured by it. Of course this depends heavily on the experiment in question and some drugs (like psychological ones) have a higher placebo effect than others. A lot of people seem to have the idea that the placebo effect is very big for medication outside of experiments - but most of the time it's very small to non-existing.
- Semaphor 14y ago
  Considering the placebo effect (unless you think bioresonance therapy is true) cured me of several allergies, I'm pretty happy with how strong it is:)
  - mistercow 14y ago
    Or your allergies just went away as you got older, and you attribute that to the placebo effect.
    - pygy_ 14y ago
      There are complex interactions between the nervous and immune systems. I don't think that anything has been demonstrated regarding allergies, but I wouldn't rule out a therapeutic effect in this case. The absence of evidence is not an evidence of absence.