Health improvement strategies can involve whole population approaches, targeted programmes directed at individuals (high-risk approach) or at populations at greater risk (directed-population approach), or a mixture of approaches [1–6].
The high risk approach aims to prioritise interventions to those identified (often through screening) as at increased-risk. While often used, its limitations are well-recognised . The directed-population approach normally uses epidemiological and/or social data to define the particular population subgroup . It is has been shown, however, that such approaches can also present challenges, and targeting all (or the majority of) individuals considered at greatest need can be difficult to achieve [9–12]. This is particularly challenging when resources are limited, disease is widely dispersed, and other social, cultural and political factors have to be considered.
Notwithstanding the above, it is recognised that a combination of approaches is often the most appropriate option for strategies aimed at health improvement and reductions in health inequality. This is in keeping with the Marmot Review  of 2010 which introduced the concept of “proportionate universalism”, whereby to reduce the steepness of the social gradient in health, interventions must be universal but with a scale and intensity that is proportionate to the level of disadvantage faced.
Despite recent improvements in the oral health of children in Scotland, dental caries remains a highly prevalent disease with persisting inequalities. The most recent National Dental Inspection Programme (NDIP), which monitors the oral health of Scottish primary school children, found that overall, 33% of 5 year old primary 1 (P1) children had caries experience, and in the most deprived areas of Scotland, this figure rose to 49.5% . In addition it has been established that the incidence of new cavities is much higher in children with caries than those free of caries, and therefore there is an imperative to prevent the development of caries in high-risk caries free children .
Childsmile, the national oral health improvement programme for children in Scotland aims to use a proportionate universalism approach to improve the oral health of children and reduce inequalities in dental health and in access to dental services. Within the programme, every child born in Scotland has access (from six months of age) to a programme of care within Primary Care Dental Services (PCDS), with the intensity of support tailored to the needs of individual families. This involves dietary advice and signposting to relevant local community development activity, toothbrushing demonstration and provision of supplies for home use and twice yearly application of fluoride varnish to the teeth. Additionally, supervised daily toothbrushing is provided to every 3 and 4-year old child attending nursery school (both local authority and private). In an attempt to ensure that the scale and intensity of the intervention is proportionate to the level of need, additional support is directed to children at increased-risk of decay through home and community support , and also via a nursery/school-based fluoride varnish clinical preventive programme that targets 20% of children attending priority nurseries and primary schools. This approach complies with current guidelines recommending twice yearly application of fluoride varnish for all children, increasing to four applications per year for those deemed at increased-risk of caries.
The method of targeting those children most in need of the additional nursery/school-based intervention is based on ranking schools within each Health Board area in Scotland according to those with the highest percentage of P1 pupils with a home postcode in the most deprived quintile of the Scottish Index of Multiple Deprivation (SIMD) (an area-based indicator of deprivation) . Within each Health Board, all P1 children within the highest ranking schools are selected to receive the intervention until 20% of the P1 population has been reached, then no further schools are selected. It has been argued, however, that in some remote and rural areas, deprivation based methods, even when applied locally as opposed to nationally for Scotland, are not appropriate. Instead it has been suggested that in these areas the method of targeting should be based on caries experience (i.e. disease prevalence).
As this directed-population approach component of the overall Childsmile intervention involves a clinical approach to prevention, in some ways it has the same limitations as those of a high-risk strategy approach in that it is not directed at the underlying determinants of disease and therefore new high-risk children will be constantly emerging . Thus, while it does not attempt to identify all high-risk children at an individual level, it is relevant to determine if this clinically-based approach, delivered in a school setting, reaches those at greater need.
This paper aims to use the Childsmile model to compare the effectiveness of a number of different methods for identifying individuals at increased-risk when a directed-population approach is taken within the usual economic, social and cultural constraints.
The aims of the study are:
To establish what proportion of children targeted for intervention are actually at increased-risk using four different targeting methods and three different definitions of increased-risk
To describe how these findings vary across Health Boards within Scotland
To explore the effect of targeting at the national versus local Health Board level
To determine for each method and each definition of increased-risk the proportion of children screened in and screened out at a Scotland level
To identify the most effective method of targeting children for this intervention