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Pathfinder survey

Extracts of the Fourth edition of
"Oral Health Surveys - Basic methods", Geneva 1997.

This extract concerns: Pathfinder methodology. Pages 5 - 9.

Design of a Basic Oral Health Survey

"Pathfinder" surveys

Pathfinder surveys can be either pilot or national, depending on the number and type of sampling sites and the age groups included.

A pilot survey is one that includes only the most important subgroups in the population and only one or two index ages, usually 12 and one other age group. Such a survey provides the minimum amount of data needed to commence planning. Additional data should then be collected in order to provide a reliable baseline for the implementation and monitoring of services.

A national pathfinder survey incorporates sufficient examination sites to cover all important subgroups of the population that may have differing disease levels or treatment needs, and at least three of the age groups or index ages (see page 7). This type of survey design is suitable for collection of data for planning and monitoring of services in all countries whatever the level of disease, availability of resources, or complexity of services. In a large country with many geographic and population subdivisions and a complex service structure, a larger number of sampling sites is needed. The basic principle of using index ages and standard samples in each sites within a stratified approach, however, remains valid.

The following method is recommended as a general guideline for basic oral health surveys for the planning, monitoring and evaluation of oral care services.

Subgroups. The number and distribution of sampling sites depend upon the specific objectives of the study. Sampling sites are usually chosen so as to provide information on population groups likely to have different levels of oral disease. The sampling is usually based on the administrative divisions of a country - the capital city, main urban centres, and small towns or rural areas. In countries where there are different geophysical areas, it is usual to include at least one sample site in each area type.

If there are several distinct ethnic groups in the population with known, or suspected, differences in levels of oral disease, it may be necessary to include separate samples of each of these groups in the main subdivisions for the survey. However, maximum use should be made of available knowledge about variations between the different groups in order to limit the number of additional subsamples needed. Once the different groups are decided upon, application of random sampling of subjects within the groups is desirable.

The assistance of local health administrators can be very useful when the final decision is made as to which population subgroups are significant for the study and should be represented in the final sample. For a national pathfinder survey, between 10 and 15 sampling sites are usually sufficient. If, however, there are large urban centres in the country, it may be necessary to locate several additional sampling sites in at least two cities.

Index ages and age groups. The following ages and age groups are recommended: 5 years for primary teeth and 12, 15, 35-44 and 65-74 years for permanent teeth.

    (a) 5 years. Where it is practical and feasible, children should e examined between their 5th and 6th birthdays. This age is of interest in relation to levels of caries in the primary dentition which may exhibit changes over a shorter time span than the permanent dentition at other index ages. In some countries 5 years is also the age at which children begin primary school.

    Note: In countries where school entry is later, e.g. at 6 or 7 years, these ages can be used, though the mean age should be reported with the results. In these older age groups, missing primary incisor teeth should not be scored as missing because of the difficulty in differentiating between primary incisors lost due to exfoliation and those lost because of caries or trauma.

    (b) 12 years.This age is especially important, as it is generally the age at which children leave primary school, and therefore in many countries, is the last age at which a reliable sample may be obtained easily through the school system. Also, it is likely at this age that all permanent teeth, except third molars, will have erupted. For these reason, 12 years has been chosen as the global monitoring age for caries for international comparisons and monitoring of disease trends.

    In some countries, however, many school-age children do not attend school. In these circumstances, an attempt should be made to survey two or three groups of non-attenders, from different areas, in order to compare their oral health status with that of children attending school.

    (c) 15 years. At this age the permanent teeth have been exposed to the oral environment for 3-9 years. The assessment of caries prevalence is therefore often more meaningful than at 12 years of age. This age is also important for the assessment of periodontal disease indicators in adolescents. In countries where it is difficult to obtain reliable samples of this age group, it is usual to examine 15-year-olds in two or three areas only, i.e. in the capital city or other large town and in one rural area.

    (d) 35-44 years (mean = 40 years). This age group is the standard monitoring group for health conditions of adults. The full effect of dental caries, the level of severe periodontal involvement, and general effects of care provided can be monitored using data for this age group. Sampling adult subjects is often difficult. Samples can, however, be drawn from organized groups, such as office or factory workers. Use may also be made of readily accessible groups, e.g. at a market, to obtain a reasonably representative sample in situations where truly representative sampling is not feasible. Care must be taken to avoid obvious bias, such as sampling patients at medical care facilities.

    (e) 65-74 years (mean = 70 years). This age group has become more important with the changes in age distribution and increases in life-span that are now occurring in all countries. Data for this group are needed both for planning appropriate care for the elderly and for monitoring the overall effects of oral care services in a population. Examination of representative members of this age group is often not as difficult as for the previous age group, as elderly people are more likely to be found in or near their homes, or in day centres or institutions and can therefore be examined during the day. Nevertheless, care should be taken to sample adequately both house-bound and active members of this age group.

Number of subjects. The number of subjects in each index age group to be examined ranges from minimum 25 to 50 for each cluster or sampling site, depending on the expected prevalence and severity of oral disease.

An sample of a sample design for a national pathfinder survey for each index age or age group is as follows:

Urban 4 sites in the capital city or metropolitan area (4 x 25 = 100)
2 sites in each of 2 large towns (2 x 2 x 25 = 100)
Rural 1 site in each of 4 villages in
different regions
(4 x 25 = 100)
Total 12 sites x 25 subjects = 300

If this cluster distribution is applied to four index ages in the population under study, the total sample is 4 x 300 = 1200.

Such a sample design permits the identification of significant differences between urban and rural groups and, in certain situations, between different socioeconomic groups in the capital city or large towns. Areas where the disease prevalence is either much higher or much lower than the national average may also be identified from the results of such a survey.

However, a total 25 subjects, with approximately equal numbers of females and males, is sufficient only in populations where caries and periodontal disease levels are estimated to be low or very low. In populations where these disease levels are known to be moderate or high - e.g. the percentage of caries-free 12-year-olds is 5-10 % or lower - the standard size for each sample should be 40-50 subjects.

If the level of dental caries in the population is unknown, it will be necessary to estimate the level of disease before starting a survey. A rapid and effective way of estimating the prevalence of caries in a population is by classifying a group of subjects as caries-free or not. For example, it should be possible to examine two or three classes of 12-year- olds of different socioeconomic levels, in two or three local, easily accessible schools, where the widest possible differences in disease may be expected. If more than 20 % of the children in the class are caries-free, the caries prevalence is low; if 5-20% are caries-free, the prevalence is moderate; and if fewer than 5 % are caries-free, the prevalence is high. This estimate of prevalence may then be used as a guide when deciding on standard sample size and when completing the protocol.

For a discussion about the "Level of precision" - see "Extracts of the Third edition of Oral Health Surveys - Basic methods, Geneva 1987.

Last updated by Gisela Ladda Tayanin