Reisman 1990.

Methods	Double‐blind, cross‐over, randomised controlled trial
Participants	40 subjects with perennial allergic rhinitis and/or asthma and confirmed allergy to house dust mite
Interventions	Group 1: HEPA loaded with an active Enviracaire filter for 4 weeks followed by placebo for 4 weeks Group 2: same as Group 1 but order of active and placebo filters reversed
Outcomes	Particulate counts in bedroom air Symptom and medication scores Patients' subjective response to treatment
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	The randomisation technique in this trial was not described
Allocation concealment?	Low risk	"A double‐blind study"
Blinding?	Low risk	Patients and investigators were both blinded to the order in which filters were deployed in the HEPAs
Incomplete outcome data addressed? All outcomes	Low risk	The drop‐outs in both groups were described fully and intention‐to‐treat analysis was performed
Free of selective reporting?	Low risk	No evidence of selective reporting
Free of other bias?	High risk	It was unclear whether the decision to only compare data from the last 2 weeks of each intervention period was decided a priori or whether this constituted a post‐hoc analysis. Follow up was short and there were difficulties in disaggregating rhinitis and asthma responses