BMC Public Health 2006, 6:42 http://www.biomedcentral.com/1471-2458/6/42 FFiingeupraert1icle levels by pub category on one night's monitoring, September 2005 Fine particle levels by pub category on one night's monitoring, September 2005. affecting occupants' behaviour, investigators acted as nor- mal customers and bought a drink before moving to the sampling area. The bag was carried or placed on a seat or table wherever possible to sample the ambient air. We recorded the place of monitoring within the venue and time of entry. Record- ing occurred for at least 30 minutes and usually lasted about 30–35 minutes. We recorded whether or not special events likely to affect occupancy, such as quiz nights, were taking place. Analysis We calculated a time-weighted average PM2.5 level for each venue, and the mean PM2.5 levels by the four pub types and by deprivation and food-serving categories separately. PM2.5 levels generally had a highly positively skewed dis- tribution, so significance tests were performed using log transformed data, and geometric means are also reported where appropriate. Ethics Ethical approval was not required for this study as no measurements were made on human subjects. Results Of 402 pubs in the sampling frame, 71% were in deprived areas (IMD4-5). Only nine refused to take part. Monitor- ing was completed in 64 pubs, 16 in each study area. Equal numbers from each pub category were sampled on each evening except for one night in Burnley when a food- serving pub from a deprived area was substituted for a non food-serving pub. The mean time of starting monitoring by type of pub was as follows: affluent food-serving 8.58 pm (range 7.15 to Page 3 of 6 (page number not for citation purposes)