Questions about drug use were asked using a computer-assisted self-completion interview (CASI), as in the 2000 and 2007 surveys. They covered lifetime experience of 15 types of named drug, together with use in the past year. The drugs asked about are those considered to be mostly widely used. New psychoactive substances (NPS) were not included.
Each survey involved interviewing a large stratified probability sample of the general population, covering people living in private households. The full adult age range was covered, with the youngest participants aged 16 and the oldest over 100.
The resulting statistics for illicit drug use have been age-standardised. This is because the prevalence of use of illicit drugs is related to age and the age profile (the number of people of different ages within an ethnic group) can differ considerably between ethnic groups. This adjustment allows comparisons to be made between ethnic groups as if they had the same age profile.
The survey covers people who live in private households. It doesn’t include those who live in institutional settings or in temporary housing (such as hostels or bed and breakfasts) or those who sleep rough.
Where a selected participant could not take part in a long interview due to a physical or mental health condition, some information about this was recorded by the interviewer on the doorstep. This information may be biased due to it having been collected from another household member.
Socially undesirable or stigmatised feelings and behaviours may be underreported. While this is a risk for any study based on self-report data, the study goes some way to minimising this by collecting particularly sensitive information in a self-completion format.
Some people selected for the survey could not be contacted or refused to take part. The achieved response rate (57%) is in line with that of similar surveys (Barnes et al. 2010; cited in APMS 2014). Weighting helps take account of those who were selected for the survey but didn’t take part.
Weighting is used to adjust the results of a survey to make them representative of the population and improve their accuracy. For example, a survey which contains 25% women and 75% men will not accurately reflect the views of the general population which we know is around 50% men and 50% women.
More detailed information on the weighting used here can be found on page 24 of the Methods chapter of the Adult Psychiatric Morbidity Survey 2014 (PDF).
The confidence intervals for each ethnic group are available in the ‘download the data’ section.
6.2% of White British women surveyed used illicit drugs in the 12 months prior to the survey. This is a reliable estimate of the percentage of White British women in England who used illicit drugs in that time period. Because the APMS results are based on a random sample of adults aged 16 or older, however, it’s impossible to be 100% certain of the true percentage.
It’s 95% certain, however, that somewhere between 5.2% and 7.3% of all White British women in England used illicit drugs in the 12 months prior to the survey. In statistical terms, this is a 95% confidence interval. This means that if 100 random samples were taken, then 95 times out of 100 the estimate would fall between the lower and upper bounds of the confidence interval. But 5 times out of 100 it would fall outside this range.
The smaller the survey sample, the more uncertain the estimate and the wider the confidence interval. For example, fewer women from the Black/Black British ethnic group were sampled for this survey than British White women, so we can be less certain about the estimate for the smaller group. This greater uncertainty is expressed by the wider confidence interval of between 5.3% and 17.1%.
Suppression rules and disclosure control
Risk to disclosure has been accounted for with limitations of the level of disaggregation, size of category groupings, and the maintaining of large underlying populations for analysis. No further suppression or other disclosure control has been applied.
Percentages have been rounded to one decimal point.
Full references for other sources cited in this commentary can be found in the Adult Psychiatric Morbidity Survey: Survey of Mental Health and Wellbeing, England, 2014.Quality and methodology information