Alan Maynard's criticism of the quality improvement efforts under way for more than a decade in the NHS, and specifically of the role of the Institute for Healthcare Improvement in that work, abounds with misunderstandings, write Stephen Thornton and Don Berwick

His claim that improvement programmes suffer from a 'paucity of evidence' regarding costs and effects is simply not true (To read Alan Maynard's column, click here). By their nature, effective system improvement projects, correctly conducted, are rich in data. Hundreds of hospitals in the US, the UK and elsewhere have for years increased their skills in local measurement, small-scale tests of change and assessment of results. What they find is not surprising: improvement initiatives based on scientific evidence sometimes work well in clinical settings, and sometimes do not.

To claim that the lessons learnt are not documented - that the work is simply 'faith-based' - is a dramatic overstatement. Formal cost-effectiveness analyses linked to improvement projects are still sparse, and in that sense we agree with Professor Maynard that more would be desirable. However, his comment ignores the volume of relevant commentary, evaluative studies and original reports that have emerged in the past few years. Several peer-reviewed journals now exist, devoted to reports and assessments of this type, and we can track more than 40 peer-reviewed articles published by IHI faculty alone in the past three years.

The IHI has been involved in attempts to speed improvement of NHS care for more than a decade. Projects have been disciplined, some results superb, and most experience informative. We deeply regret Professor Maynard's dismissive characterisation of these dedicated endeavors as 'evangelical'. If he means this pejoratively, then it is disrespectful of the intelligent, creative and searching activities of our colleagues on both sides of the Atlantic.

One case in point is the superb work of four UK hospitals, working with the IHI in the Health Foundation's safer patients initiative. This is one of the most generative and successful efforts we have ever seen to try to reduce medically caused injuries to patients. It is based on a series of clinical and managerial interventions which are evidence based.

The learning from this project has been well-documented in project reports and has featured in national and international conferences. These hospitals have learned the importance of measurement as a core part of their work. They are well attuned to its financial implications. The recent expansion of the initiative to a second wave of 20 trusts will yield even more information and lessons for the pursuit of safer care, and of the costs and benefits thereof. The whole project is being fully evaluated by a team led by Professor Richard Lilford at Birmingham University.

Maynard's assertion that 'economic sanity has failed to be incorporated' into the advocacy and decision-making of people, like us, who are trying to make care safer is an unfounded indictment. Trying to make care ever safer is an important enterprise for all of us in health care. Doing this as efficiently as we can with due attention to the opportunity costs is necessary and obvious. Neither colleagues at the IHI, nor at the Health Foundation, nor in the hospitals with which we work are blind to resource issues nor unaware of constraints. We seek improvement that is wise and investments that are smart. In pursuit of these complex goals, we welcome dialogue and strongly prefer it to diatribe.

Stephen Thornton is chief executive of the Health Foundation and Don Berwick is president of the Institute for Healthcare Improvement.