The study was carried out by a group of international scientists from a number of universities and research institutes in Australia, Europe, UK, Japan, Singapore, China and North America. The team was led by researchers at the International Laboratory for Air Quality and Heath based at Queensland University in Australia.

The claim is evidence-based because airborne transmission of COVID-19 via small microdroplets (aerosols) has been identified by several hospital-based studies, so eliminating or dispersing these aerosols should reduce virus transmission rates. Furthermore, even without the risk of COVID-19, it is well established that it is important to ventilate or purify indoor air in order to reduce pollution because of the associated health risks.

The study’s authors quantify the rate at which air should be replaced for some examples (such as room size and number of people) and alert readers to the fact that the World Health Organisation recommends a higher rate during a pandemic, which gives further authority to the study’s claims. Very usefully for the public, the study also gives practical advice about ventilating houses and flats by opening windows and using extractor fans whenever possible, and by making sure central heating systems are maintained as winter approaches.

The report is based on different studies carried out in many countries around the world, so globally or near global.

Because the study brings together and assesses the results of a number of studies each with their own sampling rates and methods, no single sample size can be calculated.