Changing beliefs about health led to small-to-medium changes in what people did.

The review

1. 01

   Who took part

   The review pooled 204 experiments from 155 studies, with college students, the general public, workers and school pupils. The paper does not give one total number of people.

2. 02

   What they did

   In each experiment, one group was helped to change its beliefs about a health habit. The beliefs were about the habit's outcomes, what others did, or how sure people felt they could manage it. The other group got nothing special, or a different treatment.

3. 03

   What happened

   Helping people feel surer of a habit led to the biggest change in what they did. Changing attitudes or what people thought others did led to smaller changes, and changing more than one belief at once added nothing. The experiments showed about half the size of effect that the correlation studies had shown.

What the review found

1. Helped

   Across 90 experiments (29,520 people), helping people feel more sure of a habit led to more of it.

   Pooled analysis of 90 studies with 29,520 people · vs the other groups · ⚠ whole programmes were tested, so no single part can be credited

2. Helped

   In 67 experiments (31,328 people), changing what people expected from a habit led to more of it.

   Pooled analysis of 67 studies with 31,328 people · vs the other groups · ⚠ whole programmes were tested, so no single part can be credited

3. Helped

   In 17 experiments (9,337 people), changing what people thought others did led to more of the habit.

   Pooled analysis of 17 studies with 9,337 people · vs the other groups · ⚠ whole programmes were tested, so no single part can be credited

Source