Wright 2009.

Study characteristics
Methods	Random number generator, sequential blocks of 4, automated telephone‐answering system
Participants	N = 119 (100 in analyses) Age range 16 to 60 years Positive skin test
Interventions	Test: mechanical heat recovery ventilation system Control: placebo mechanical heat recovery ventilation system Allergen eradication was carried out in all homes. Carpets were cleaned, new pillows, duvets and mattress covers were supplied to all participants.
Outcomes	Peak flow, asthma symptoms, medication usage, visits to hospital
Notes	18 major protocol violators (machine inadvertently turned on)
Risk of bias
Bias	Authors' judgement	Support for judgement
Allocation concealment (selection bias)	Low risk	See above