Dividing the participants three ways, they discovered points of note. The groups included two (out of three) that were provided with air cleaners and professional coaching on smoke exposure. The third group had neither equipment nor coaching provided. Concerning symptoms experienced by the children involved, who were asthmatic, the difference between the two groups provided with air-cleaning equipment was negligible. Provision of a health coach, whose advice was confined to the issue of secondary smoke exposure, did not make any difference to the children's symptoms.
Only smoking households were included and so no comparison was made between smoking and non-smoking households using air-cleaning equipment.
The authors still felt they could conclude: 'Although the use of air cleaners can result in a significant reduction in indoor PM concentrations and a significant increase in symptom-free days, it is not enough to prevent exposure to secondhand smoke.' Their reasoning was that they could still detect nicotine in the children even though the air cleaning equipment was in use.
This is where my understanding of the issues is somewhat patchy. I am struggling a little to see what damage is being done in the context of this study if the symptoms of subjects are being relieved. So what, if there is trace cotinine in the urine of those children?
The study itself was set up by a body known as PREACH (yes, PREACH): Particulate Reduction Education in City Homes. In terms of a study it is deliberately vague, for example it says that people are given HEPA air cleaners, but this isn't very useful information as even a brief search will show quite a few different models. Since the study seems designed to show, not that air cleaning systems work but that they are of limited use against secondary smoke, it is interesting that they don't specify which model they are using – they would surely have indicated if they had used a top-of-the-range model. In fact they are not interested in the technicalities, only in the goal of reducing parental smoking.
Perhaps they were irked by the results, especially that providing a health coach didn't improve the children's symptoms! Their focus on smoke as the only relevant pollutant is quite marked as we see in the press release linked above. For example:
Parents should be counseled to implement a total ban on indoor smoking and use air cleaners only as a temporary tool on the way to achieving a smoke-free household, the Hopkins team concludes in the Aug. 1 issue of the Archives of Pediatrics & Adolescent Medicine. [emphasis added]and:
Because smoking is a main driver of indoor air pollution, the researchers recommend the use of air cleaners even in smoke-free homes if they are part of multi-family dwellings in which second-hand smoke can easily seep in from surrounding units.This even though the single greatest difference made to symptoms in the study was made by the provision of air-cleaning equipment. It is quite extraordinary to advise parents to dump the air cleaning equipment once they have managed to stop smoking, and shows pretty near tunnel vision and misunderstanding of the purpose of the equipment. They only use they perceive for this equipment in non-smoking households is to protect against smoke entering the apartment from other flats ... this eventuality in itself probably a fantasy.
It is excellent that at least they have started looking into the use of these machines to help relieve air quality problems in people's homes. It would be even more productive to abandon attempts to re-educate parents into reducing the time they spend with their offspring if such education, as in this study, makes no clear difference to the outcome.