Table 1 Key concepts included in the IHC mass media (podcast) and primary school resources

Treatments may be harmful. People often exaggerate the benefits of treatments and ignore or downplay potential harms. However, few effective treatments are 100% safe (included in podcast episode 1)

Personal experiences or anecdotes (stories about how a treatment helped or harmed someone) are an unreliable basis for predicting the effects of most treatments (included in podcast episode 3)

A treatment outcome may be associated with a treatment, but not caused by the treatment. The fact that a possible treatment outcome (i.e. a potential benefit or harm) is associated with a treatment does not mean that the treatment caused the outcome. The association or correlation could instead be due to chance or some other underlying factor. For example, people who seek and receive a treatment may be healthier and have better living conditions than those who do not seek and receive the treatment. Therefore, people receiving the treatment might appear to benefit from the treatment, but the difference in outcomes could be because they are healthier and have better living conditions, rather than because of the treatment (included in podcast episode 4)

How widely or how long a treatment is used is not a reliable indicator of how beneficial or safe it is. Treatments that have not been properly evaluated but are widely used or have been used for a long time are often assumed to work. Sometimes, however, they may be unsafe or of doubtful benefit (included in podcast episode 5)

New, brand-named, technologically impressive, or more expensive treatments may not be better than available alternatives

Opinions of experts or authorities do not alone provide a reliable basis for deciding on the benefits and harms of treatments. Doctors, researchers, patient organisations and other authorities often disagree about the effects of treatments. This may be because their opinions are not always based on systematic reviews of fair comparisons of treatments (included in podcast episode 6)

Conflicting interests may result in misleading claims about the effects of treatments. People with an interest in promoting a treatment (in addition to wanting to help people) - for example, to make money - may promote treatments by exaggerating benefits, ignoring potential harmful effects, cherry picking which information is used, or making false claims. Conversely, people may be opposed to a treatment for a range of reasons, such as cultural practices

 Evaluating the effects of treatments depends on making appropriate comparisons. If a treatment is not compared to something else, it is not possible to know what would happen without the treatment, so it is difficult to attribute outcomes to the treatment (included in podcast episode 2)

 Comparisons of treatments must be fair. Apart from the treatments being compared, the comparison groups need to be similar at the beginning of a comparison (i.e. “like needs to be compared with like”) (included in podcast episode 7)

If possible, people should not know which of the treatments being compared they are receiving. People in a treatment group may behave differently or experience improvements or deterioration as a result of knowing the treatment to which they have been assigned. If this phenomenon is associated with an improvement in their symptoms it is known as a placebo effect; if it is associated with a harmful effect it is known as a nocebo effect. If individuals know that they are receiving a treatment that they believe is either better or worse than an alternative (that is, they are not “blinded”), some or all of the apparent effects of treatments may be due either to placebo or nocebo effects

Small studies in which few outcome events occur are usually not informative and the results may be misleading. When there are few outcome events, differences in outcome frequencies between the treatment comparison groups may easily have occurred by chance and may mistakenly be attributed to differences in the effects of the treatments

 The results of single comparisons of treatments (trials) can be misleading. A single comparison of treatments rarely provides conclusive evidence and results are often available from other comparisons of the same treatments. These other comparisons may have different results or may help to provide more reliable and precise estimates of the effects of treatments (included in podcast episode 8)

 Because treatments can have harmful effects as well as beneficial effects, decisions should not be based on considering only their benefits. Rather, they should be informed by the balance between the benefits and harms of treatments. Costs also need to be considered (included in all episodes)