Dear Editors,

We appreciate the interest of Dr Dwyer-Hemmings in our historical review.^{Reference van Munster, Zamanipoor Najafabadi, Schoones, Peul, van den Hout and van Benthem1} Moreover, we are grateful for the dedication with which Dr Dwyer-Hemmings clarified some explanatory factors from the UK experience. Although we could not give such a detailed description, given the large number of countries included in the studies discussed in our review, we agree that this description helps us to understand regional variation and eventually to tackle unwarranted variation.

Our review demonstrated that a significant number of articles failed to account for explanatory factors such as age and socioeconomic status. As a result, we concur with Dr Dwyer-Hemmings that future research in this area should at least adjust for these variables. Better understanding of factors that influence regional differences in tonsillectomy rates in other countries can indicate which other variables should be adjusted for. The use of large administrative databases in this research area enables us to more easily investigate large geographical regions over time. However, these databases might not always be sufficient to account for individual practitioner decision-making.

We indeed feel that the explanation of the UK's historical experience helps us understand why variance persists and, consequently, determine which interventions are appropriate to reduce variation if unwarranted. Other countries should analyse the factors that attribute to regional variation and consider how to tackle unwarranted variation accordingly.

The other structural, financial and political factors that attributed to the rise in number of tonsillectomies in the UK, as stated by Dr Dwyer-Hemmings, do not automatically justify this increase elsewhere. In the Netherlands, we found that efforts from the Dutch Society of Otolaryngology/Head and Neck Surgery to develop and implement evidence-based guidelines, as part of a quality of care cycle on this topic, led to a significant decrease in numbers of tonsillectomies and adenoidectomies (−39 per cent and −49 per cent between 2005 and 2018).^{Reference van Munster, Zamanipoor Najafabadi, van 't Hooft, van Barneveld, Böhringer and Visser2} We are hopeful that similar findings apply to the extent of unwarranted regional variation and we are curious about results from other countries.