Sampling and study population
Data were generated from the National Alcohol Diary Survey (NADS) (20). The NADS was a nationally representative cross-sectional survey of a stratified clustered sample of 5991 individuals aged 18–75 years living in private households in Ireland. The sampling frame used for the study was the An Post/Ordnance Survey Ireland GeoDirectory database, a list of all addresses in the Republic of Ireland, distinguishing between commercial and residential dwellings. A multi-stage probability approach to sampling was used. The first stage involved the selection of geographical areas. The second stage involved stratifying the sample according to social class and degree of urbanity to ensure that selected geographical locations were representative of the population. All households selected through this sampling process were visited during the fieldwork period and all adults aged 18-75 years in each household were invited to participate.
Respondents completed a face-to-face interview and self-completed questionnaire. Interviews were administered in participants’ own homes by professional social interviewers via a Computer Assisted Personal Interview (CAPI). Interviews were completed between July and October 2013; the household response rate was 67.2% and the within household response rate was 77.1%. The survey was granted ethical approved by the Royal College of Physicians of Ireland and all participants gave written informed consent for their data to be used for research purposes.
Number of standard drinks consumed in last week
Over two-thirds (69.1%, n=2997) of those who consumed alcohol in the last 12 months also consumed alcohol in the week prior to the survey. Participants were asked to report all alcohol consumed in the week prior to survey. A standard drink in Ireland contains 10g of pure alcohol and is equivalent to half a pint of beer, a single pub measure of spirits (35ml), or a small (100ml) glass of wine. Respondents were provided with beverage-specific flash cards so they could accurately report how many standard drinks they consumed.
Heavy episodic drinking
For the purpose of this study, heavy episodic drinking (HED) was defined as consuming 60g or more of pure alcohol in a single drinking occasion (17). Respondents were asked how frequently they consumed six or more standard drinks on a single occasion and given the following response options: “everyday”, “5–6 times a week”, “4 times a week”, “3 times a week”, “twice a week”, “once a week”, “2–3 times a month”, “once a month”, “6–11 times a year”, “2–5 times a year”, “once in the last 12 months” and “never”.
Alcohol dependence was defined according to DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, 4th Edition) criteria, and was measured via self-completed questionnaire using the ten items that denote alcohol dependence from the Composite International Diagnostic Interview (22). Alcohol dependence was established from a positive response in three or more of the seven domains on the DSM-IV diagnostic criteria in the twelve months before the interview. Only participants who had complete information on both the DSM-IV and on frequency of heavy episodic drinking (HED) were included in the analyses (n=4338).
Classification of drinkers
Current drinkers were defined as those who had consumed alcohol on at least one occasion in the last year. Non-drinkers (n=1236, 20.6%), defined as those who had not consumed any alcohol in the last 12 months, were excluded from the analyses. Drinkers were placed into one of the four categories below based on frequency of HED and whether they met the criteria for alcohol dependence:
Alcohol dependence: Respondents who met the DSM-IV criteria for alcohol dependence were classified as dependent drinkers (n=299, 6.9%).
Monthly HED: Respondents who reported consuming six or more standard drinks at least once a month and who did not meet the DSM-IV criteria for dependence were classified as monthly HED drinkers (n=1368, 31.5%).
Occasional HED: Respondents who did not meet the DSM-IV criteria for alcohol dependence and reported consuming 6 or more standard drinks between 1 and 11 times in the previous year were classified as occasional HED drinkers (n=1326, 30.6%).
Low-risk drinkers: Drinkers who did not meet the criteria for dependence and who had not engaged in HED on any occasion in the last year were defined as low-risk drinkers (n=1345, 31.0%).
Questions on eight alcohol-related harms were included in the survey. These questions were based on the “adverse social consequences of own alcohol use” from the Standardized Measurement of Alcohol-Related Troubles (SMART), a set of guidelines for the standardisation of drinking population surveys in Europe (23). Respondents were given the response options of “yes, once” “yes, more than once” and “no” as to whether they had experienced each of the harms in the last 12 months. The eight harms covered were harm to finances, harm to health, harm to work or study, harm to friendships or social life, harm to home life or marriage, been in a physical fight, been in an accident, and stopped by the police. E.g., “Have you experienced harms to your finances in the last 12 months due to your own drinking?”
Calculation of total number of alcohol-related harms
The total number of harms from drinking experienced by respondents in the survey was estimated by creating a 16-point scale based on the eight alcohol-related harm questions. Participants were assigned a score of 0 (“never”) 1 (“yes, once”) or 2 (“yes, more than once”) on each of the eight questions depending on their response. Scores on each of the eight harm questions were summed to give each participant a total score of harms that ranged from 0–16. Respondents’ scores were summed to create a total number of harms across the survey sample. This score is likely to be an under-estimation of harms, as “more than once” could equate to a number greater than 2. However, the purpose of obtaining the total harm experienced by the survey population was not to provide a precise estimate of the number of alcohol-related harms in the population but was to estimate how the harms were distributed across each drinker type. Hence the scoring of the scale in this way was appropriate to the aim of the study.
Statistical analyses were carried out using Stata version 15 (Stata Corporation, College Station, TX, USA) for Windows. Data were weighted with respect to age, gender and regional distribution to ensure they were nationally representative. With consideration for missing values, only valid percentages are reported. Descriptive statistics were used to describe the median (inter-quartile range) and total number of standard drinks consumed by respondents. Associations between socio-demographic variables and drinker type were analysed by cross-tabulations and significance was assessed by the Pearson χ2 test. Socio-demographic variables analysed were age, gender, employment, marital status and income. Associations between drinker type and each of the harms experienced from own drinking were analysed by cross-tabulations, using the Pearson χ2 test to test for statistical significance. For all analyses an alpha level of p<.05 was considered to be statistically significant.