Under-reporting of alcohol consumption
2.7.1 Summary of findings
This literature review has identified changing drinking habits in England, signified by the changing nature of the composition of alcohol sales. Changes in drinking patterns will be associated with shifts in the causes of under-reporting, so the relative contribution of each of the following findings to under-reporting may change in space and time. The literature on the potential mechanisms by which under-reporting of alcohol consumption takes places has been systematically reviewed and critically appraised.
With regard to non-response, the evidence that non-responders drink more than survey participants is uncertain. There is some evidence that participants who are difficult to contact drink more than those who are easier to contact, however the continuum of resistance theory (that late responders are more similar to non-responders) is somewhat speculative. Little is known about the characteristics of non-responders who do not respond to repeated attempts as a fact of their aversion to taking part in research studies. It could be hypothesised that non-responders may be experiencing illness, or lead chaotic lifestyles and be heavier drinkers, but
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this is unknown. Further research on the characteristics of late responders or those who are difficult to contact would be welcome for alcohol as well as a range of health behaviours.
Similarly difficult to investigate to non-response is the idea of selective reporting, or deliberate under-reporting. There is evidence that participants under-report their consumption more if they have a health condition which precludes drinking such as pregnancy or HIV infection. Whether social desirability bias leads to selective reporting is less certain, however there is some suggestion of a small effect leading to increased under-reporting. There are only a small number of studies of social desirability bias so whether the effect of a health condition is similar to that of the presence of a spouse or child is not known.
The evidence that mode effects influence survey estimates of alcohol consumption is much more convincing. Self-completion questionnaires or diaries yield higher estimates of consumption than face-to-face or telephone interviews. Caution should be taken when comparing different questionnaire types delivered in different modes, however, as there may be other factors which influence this difference between the two methods. For example, where a diary is compared with a face-to-face interview, as in (124), the additional effect of the prospective nature of the diary should be considered.
There is an extensive literature on how questionnaire design can mitigate recall bias in social surveys measuring alcohol consumption. Careful and consistent phrasing of questions appears to be important for normalising particular consumption levels. This would particularly apply in face-to-face surveys where an interviewer is present. Studies which have used test-retest methods to explore the effect of questionnaire design have quite consistently found that more detailed questions, beverage specificity, and a short recall period (or prospective nature) all help to achieve higher alcohol consumption estimates. As a result, the 'gold standard' measure of drinking is a self-completion prospective drinking diary with beverage specific questions and takes account of drink size. Studies which have specifically investigated length of recall period have had mixed findings, and may be partly due to the heterogeneity between studies in terms of design and recall periods studied.
The fact that survey participants may under-estimate their alcohol consumption due to lack of knowledge of drink strengths (ABV) or volumes is often cited in the literature as one reason for the 'missing units', however remarkably little research has addressed this topic. There is convincing evidence that participants pour more than one standard drink or unit when asked to pour their usual glass or a standard drink. However, very little is known about participants' perceptions of how much alcohol is in their usual glass: only one study was identified and this was conducted among 65-74 year olds in Australia. As many modern social surveys about
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alcohol consumption (such as the HSE) take drink size into account (rather than recording each drink reported as one unit or standard drink), participants' perception of their drinks is important.
This is a potentially substantial area of under-reporting, but current knowledge is not able to verify its contribution to under-reporting.
It is intuitive that there would be an inverse relationship between levels of intoxication and reporting accuracy. The use of biological and observational measures to verify self-report is an exciting and growing area of research. The use of objective biological measures to verify self-report is mixed, but supports this hypothesis where studies of students - who may be overly- keen to report heavy drinking - are excluded. Only two studies have verified self-reports using observational methods and these have been successful in identifying under-reporting being greater among the heavier-drinking participants. More studies investigating the shape of the relationship between intoxication and reporting accuracy would be welcome, but ethical issues must be considered.
2.7.2 Conclusions
This literature review has identified several areas of under-reporting which may contribute to the
‘missing units’. Many of these concern the failure of social surveys to account for the complexity of participants’ lives, and arise from the fact that it is of little benefit to the participants to ensure the information they provide is accurate. With the shift towards private or off-premise drinking in England in recent years, the potential for under-estimation to contribute to the missing units may have grown. Research on the extent of under-estimation and its potential impact on survey data is surprisingly scarce, although data would be reasonably cheap and simple to collect. These kind of experimental studies where participants have been asked to pour drinks are relatively rare in comparison to the wealth of research on questionnaire design using test-retest procedures. Indeed, there has been relatively little methodological innovation in measuring alcohol consumption beyond changes to questionnaire design, and novel approaches such as photo-elicitation, documentary photographic or video diaries, and greater exploitation of biological measures of drinking such as BAC and TAC are encouraged.
From the systematic literature review, it is difficult to identify the relative contribution of each component of under-reporting to the total amount of under-reporting taking place in social surveys. It does appear, however, that some components of under-reporting are more definite than others. The mode in which a survey is conducted, and the design of the questionnaire, appear to be particularly important. A self-completion questionnaire or diary with detailed questions about actual consumption (as opposed to typical), using beverage specific questions that take into account drink size, and ideally a prospective design, could be expected to achieve
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the highest estimates of alcohol consumption. Very little research has addressed how under-reporting of alcohol consumption might vary in different groups, by gender, age, region, socio-economic factors, or by alcohol-related factors.
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