Tuesday, 5 May 2015

A Tale of Two Surveys

This week our crackerjack colleagues at the Propel Centre for Population Health Impact issued their most recent report on Tobacco Use in Canada. As always, this report is clear and offers important insights into the smoking behaviour of Canadians.

And, as always, the analysis is based almost entirely on the Canadian Tobacco Use Monitoring Survey and its successor, the Canadian Tobacco and Drugs Survey.

These are large surveys launched in 1999 by Health Canada and administered by Statistics Canada. They ask a wide-ranging series of questions on smoking behaviour of about 14,500 Canadians. Results which were once produced every six months are now produced every two years.

The CTUMS-CTADS prevalence data gives a very rosy picture. A rousing 40% reduction in smoking prevalence since the beginning of this century.

From Propel's Tobacco in Canada 2015 report

The results of another survey conducted by Statistics Canada give a quite different picture, especially if the number of smokers are considered and not merely the prevalence.

The Canadian Community Health Survey was launched at about the same time as Health Canada's Tobacco Use Monitoring Survey.
There are only a few questions on smoking behaviour, as the survey tries to get information on a wide range of health behaviours of the 65,000 Canadians interviews. Initially results were provided every 2 years - now they are given every year.

CCHS estimates of the number of Canadian smokers provides a much less rosy picture. The reduction in the number of smokers has been a more modest 14%.

From PSC Fact Sheet: Smoking rates in Canada

The two surveys, launched in the same year and asking nearly identical questions about core smoking behaviour have been consistent in their differing results. CCHS always tracks higher.

A wise colleague once reminded me that mistakes are inevitable -- and that the real challenge is the direction of your error.  Is it not prudent to err in the direction of not understating the problem?.

 For me, that means using the CCHS data until it is proven to be less reliable, and to give profile to the number of smokers as well as smoking rates.