placebo effect

(noun)

the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work

Related Terms

Examples of placebo effect in the following topics:

  • The Clofibrate Trial

    • The Clofibrate Trial was a placebo-controlled study to determine the safety and effectiveness of drugs treating coronary heart disease in men.
    • The purpose of the placebo group is to account for the placebo effect -- that is, effects from treatment that do not depend on the treatment itself.
    • Without a placebo group to compare against, it is not possible to know whether the treatment itself had any effect.
    • This apparent placebo effect may have occurred because:
    • Adhering to the protocol had a psychological effect, i.e. genuine placebo effect.

  • Case Studies

  • Experiments exercises

    • In order to assess the effectiveness of taking large doses of vitamin C in reducing the duration of the common cold, researchers recruited 400 healthy volunteers from staff and students at a university.
    • No significant differences were observed in any measure of cold duration or severity between the four medication groups, and the placebo group had the shortest duration of symptoms.
    • One group was given 25 grams of chia seeds twice a day, and the other was given a placebo.
    • Explanatory: Treatment, with 4 levels: placebo, 1g, 3g, 3g with additives.
    • However, we must consider that a placebo effect is possible.

  • The Salk Vaccine Field Trial

    • The Salk polio vaccine field trial incorporated a double blind placebo control methodolgy to determine the effectiveness of the vaccine.
    • By the conclusion of the study, roughly 440,000 received one or more injections of the vaccine, about 210,000 children received a placebo, consisting of harmless culture media, and 1.2 million children received no vaccination and served as a control group, who would then be observed to see if any contracted polio.
    • The Salk vaccine had been 60–70% effective against PV1 (poliovirus type 1), over 90% effective against PV2 and PV3, and 94% effective against the development of bulbar polio.
    • Therefore, randomized control tends to negate all effects (such as confounding variables) except for the treatment effect.

  • Difference Between Two Means

    • These researchers found that, compared to a placebo, this drug increased total sleep duration by a mean of 61.8 minutes.
    • For example, if in the Holbrook et al. study the mean total sleep time for the placebo group were 120 minutes, then the 61.8-minute increase would represent a 51% increase in sleep time.
    • On the other hand, if the mean sleep time for the placebo were 420 minutes, then the 61.8-minute increase would represent a 15% increase in sleep time.
    • Although there is no objective answer to this question, the guidelines suggested by Cohen (1988) stating that an effect size of 0.2 is a small effect, an effect size of 0.5 is a medium effect, and an effect size of 0.8 is a large effect have been widely adopted.
    • Based on these guidelines, the effect size of 0.87 is a large effect.

  • Case study exercises

    • (b) At first glance, does acupuncture appear to be an effective treatment for migraines?
    • Researchers studying the effect of antibiotic treatment for acute sinusitis compared to symptomatic treatments randomly assigned 166 adults diagnosed with acute sinusitis to one of two groups: treatment or control.
    • Study participants received either a 10-day course of amoxicillin (an antibiotic) or a placebo similar in appearance and taste.
    • The placebo consisted of symptomatic treatments such as acetaminophen, nasal decongestants, etc.
    • (b) Based on your findings in part (a), which treatment appears to be more effective for sinusitis?

  • Using Two Samples

    • For example, researchers are interested in the effect aspirin has in preventing heart attacks.
    • Typically, one group is given aspirin and the other group is given a placebo.

  • Introduction

    • For example, researchers are interested in the effect aspirin has in preventing heart attacks.
    • Typically, one group is given aspirin and the other group is given a placebo.

  • One- and Two-Tailed Tests

    • One-tailed tests are appropriate when it is not important to distinguish between no effect and an effect in the unexpected direction.
    • The researcher would only be interested in whether the treatment was better than a placebo control.
    • It would not be worth distinguishing between the case in which the treatment was worse than a placebo and the case in which it was the same because in both cases the drug would be worthless.
    • Some have argued that a one-tailed test is justified whenever the researcher predicts the direction of an effect.
    • The problem with this argument is that if the effect comes out strongly in the non-predicted direction, the researcher is not justified in concluding that the effect is not zero.

  • Exercises

    • Do certain dosages appear to be more effective than others?
    • (AT) Create a stem and leaf plot of the number of correct responses of the participants after taking the placebo (d0 variable).
    • The April 10th issue of the Journal of the American Medical Association reports a study on the effects of anti-depressants.
    • John's wort (an herb), Zoloft (Pfizer's cousin of Lilly's Prozac) or placebo for an 8-week period.