Treatments could be harmful.

Personal experiences.

Anecdotes are an unreliable basis for evaluating the effects of most treatments.

Widely used treatments or those that have been used for a long time are not necessarily beneficial or safe.

Newer, brand-name or more expensive treatments may be no better than other available alternatives.

The opinions of experts or authorities alone do not provide reliable support for deciding on the benefits and harms of a treatment.

Conflicts of interest may result in misleading claims about treatment effects.

Evaluar los efectos de los tratamientos requiere appropriate comparisons.

In addition to the treatments being compared, the groups being compared should be similar in terms of their characteristics.

If possible, people should not know which comparator treatment they are receiving.

Small studies, in which few events occur, are generally uninformative and the results could be misleading.

Results from a single treatment comparison may be misleading.