A commonly adopted approach for the prevention of caries is the 'high-risk' strategy. For example, Messer  concluded that "... the need for, targeted prevention of dental caries for those at high risk has become apparent". The approach is based on three assumptions: first, those individuals with high future caries increments can be identified; second, measures taken to prevent the caries lesions are effective, and third, that those individuals belonging to sub-groups within a population who have previously experienced the highest levels of caries in the past will continue to do so in future. Indeed, any high-risk strategy aims to target those individuals at the greatest risk of future disease based on their current caries status or markers of disease.
From a public health perspective, what is important when deciding upon a preventive approach is what impact the measure adopted would have on the total dental health and disease burdens of the population as a whole. Even if an approach was highly accurate in predicting future caries development and the intervention was relatively successful in reducing caries in that group, the distributive features of new disease may make the proposed approach inappropriate. Even if a high-risk group had a far higher annual increment than the remaining sub-groups of the population, due to the underlying distributive properties of caries within a population, a far greater number of lesions are likely to occur in the low risk individuals because there are more of them. Batchelor and Sheiham  referred to this issue when examining caries distributions within a population. They outlined the limitations of adopting a 'high-risk' approach for the prevention of caries highlighting that any changes in the average caries experience within the population were not limited to specific sub-groups but occurred throughout the population. In addition, they found a mathematical relationship between the mean DMF score for a population and the prevalence of caries within that population. For a given mean DMF score the prevalence within the population could be defined and vice versa. The relationship was independent of both age and fluoride levels .
The problems of a high-risk strategy are increased by the low accuracy of methods used to identify the high-risk children. While the idea that an individual's future caries increment can be predicted from their past caries experience underpins the basis of caries risk assessment, the rigour of these measures to date is poor. Powell  and Zero et al.  reviewing the literature covering the use of indicators of risk found that the predictive validity of the models were heavily dependant upon the prevalence of caries and the characteristics of the population for which they were designed. Zero et al.  found that a single indicator gave as good results as more complex combinations of variables. This finding is in agreement with van Palenstein Helderman et al.  who, using longitudinal study data examining past caries variables, found that the gain in accuracy by including additional predictor variables was limited. Irrespective of their complexity, no predictive model is able to identify those individuals who will get the highest future caries increments. Hausen et al.  and Hausen  have highlighted the limitations of current methods used to identify high-risk individuals. Furthermore, even at a population level Poulsen and Scheutz  also recognised that a high-risk strategy could be challenged on the grounds of effectiveness. Examining the changes in dental caries experience in Danish children and adolescents over a ten-year period, they concluded that, if adopted, a high-risk strategy that was 40% effective would reduce the mean DMFS for the whole population by a mean of only one surface.
A major shortcoming of the high-risk approach is the failure to examine its impact on the overall number of new lesions within a population. Does a strategy targeting the high-risk group prevent more lesions for a population than a whole population strategy? Do 'low risk' sub-groups develop less new lesions than those with high caries levels? To answer the question, an analysis is required of the distribution of new caries lesions within a population as the baseline levels of caries increase.
Our critique of the high-risk strategy which we shall demonstrate in this paper is based on the concept that the largest "... burden of ill health comes more from the many who are exposed to low inconspicuous risk than from the few who face an obvious problem" . The aim of this study is to assess whether 'high risk groups' of children accounted for a high percentage of new caries lesions in children. The objective was to analyse the distribution of new lesions per 100 7-year-old children in four populations with differing initial caries levels over a 4-year period.