Better than ‘treatment as usual’ but not than other specific therapies are the headlines from the most comprehensive synthesis of motivational interviewing studies to date. Along the way are insights in to the equivocal value of manuals and of feeding back assessment results to patients.
A team of authors from the USA has produced the most comprehensive synthesis yet of studies of the influential counselling approach, motivational interviewing. The breadth of the analysis has enabled them to conduct detailed sub-analyses of relevance to practitioners and service planners.
Across all 132 comparisons, motivational interventions were associated with a statistically significant improvement in outcomes whose effect size at 0.22 is conventionally considered to represent a small impact. In a quarter of cases, the motivational intervention was roughly equivalent to the comparator, in another quarter it was associated with small positive improvements, and in a half with substantial improvements. The added benefits showed no signs of fading up to two years or more after intervention, though few studies tested this beyond a year.
The review adds its considerable weight to the common conclusion that any well structured therapy is as good as any other. However, this may be partly because studies inappropriately standardise the treatment of individuals seeking help, and equivalence of impact applies only on average across the entire caseload. It remains the case that different therapeutic styles are more or less suited to different people or people at different stages in their commitment to change.