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Pathfinder survey

Extracts of the Third edition of
"Oral Health Surveys - Basic methods", Geneva 1987.


Please observe that the Fourth edition is available, see Oral Health Methods and Indices.
This extract concerns: Pathfinder methodology. Pages 6 - 10.


Design of a Basic Oral Health Survey

"Pathfinder" surveys


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

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 index ages or age groups (see below).

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 15 years. Such a survey provides the minimum amount of data needed for commencing planning in many situations. Additional data should then be collected in order to provide a reliable baseline for the implementation and monitoring of services.

This type of survey design for collection of planning and service monitoring data is suitable for 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 locations is needed. The basic principle of using index ages and standard samples in each location within a stratified approach, however, remains valid. The process of weighting according to percentage population distribution for a specified age or age group sampled can then be applied, if necessary, to the means for grouped clusters, e.g., urban vs. rural, in order to give as close an estimate as possible for the population as a whole.

Pathfinder methodology

Subgroups. Sampling sites are usually chosen so as to provide results for population groups likely to have different disease rates. The results should be related to the administrative divisions of a countryÑthe-: capital city, main urban centres, and small towns or rural areas. In countries where there are distinct different geophysical areas, it is usual to include at least one sample subgroup in each area type.

If there are several distinct ethnic groups in the population with known, or suspected, differences in disease patterns, 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.

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. Between 10 and 15 sampling points are usually sufficient for countries with small to moderate populations. If, however, there are large urban centres in the country, it might be necessary to locate several additional sampling points in at least two cities.

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

    (a) 12 years.This age is especially important, as it is generally the age at which children leave primary school, and thus in most countries, is the last age at which a reliable sample may be obtained easily through the school system. For this reason, 12 years has been chosen as the global monitoring age for caries for international comparisons and monitoring of disease trends. However, in some countries, 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 going to school.

    (b) 15 years. Data for persons of this age can be compared with the data for 12-year-olds to provide an estimate of increases in prevalence and severity of caries; this is particularly; useful in populations for which there are no, or very little, previous data. 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.

    (c) 35-44 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 impossible. Care must be taken to avoid obvious bias, such as sampling outpatients at a dental clinic.

    (d) 65-74 years. This age group has become very much 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 thus be examined during the day.

Detailed assessment of dental caries of the primary dentition at the age of 5 and 6 years is not recommended for routine inclusion in a basic oral health survey. However, in order to monitor the achievements of preventive programmes and, in particular, disease trends, it is recommended that a count of caries-free 5- and 6-year-old children be made in one class at each school in which 12-year-olds are examined. It is also possible to record the number of primary teeth that are decayed, missing or filled; relevant codes have been included as an option on the standard WHO forms.

Number of subjects. The standard number of subjects in each index age group to be examined ranges from 25 to 50 for each cluster or sampling point, depending on the expected prevalence and severity of oral disease. The minimum number of subjects acceptable for analysis as one cluster is 20, but allowance must be made for the possibility that a subject's form may be eliminated during data processing because of operator, recorder, or examiner error. It is therefore strongly recommended that a minimum cluster size of 25 subjects per age group be examined to allow a margin for error.

However, a total of 20-25 subjects, with an approximately equal number 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 highÑe.g., the percentage of caries-free 12-year-olds is 5-10 % or lowerÑthe 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 2 or 3 classes of 12-year- olds of different socioeconomic levels, in 2 or 3 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 checklist for survey planning and sampling design (ref to Annex 2 in the Oral Health Surveys).

Level of precision

The following example is a practical guide to total sample size and is based on dental caries data for 12-year-olds. The level of precision in estimating caries prevalence (i.e., number of decayed, missing, or filled teeth (DMFT)), from a sample of 100 subjects, is shown below for low, moderate and high caries prevalence.

Caries
prevalence
Proportion of
caries-free
12-year-olds (%)
Level of precision for estimate
of DMFT for sample
size, n = 100
Low more than 20 ± 0.4
Moderate 5-20 ± 0.5
High less than 5 ± 1.0

As an example, consider a population with a moderate level of caries. A sample of 100 subjects of 12 years of age is examined, and the mean DMFT per person is found to be 4.1. This means that the value of the DMFT l for the whole population of 12-year-olds is somewhere between 3.6 and 4.6 (4.1 ±0.5). This level of precision is certainly sufficient to allow the data from such a survey to be used in planning oral care services.

The sample groups for each index age or age group can be divided as follows:

urban 4 sites in the capital city or metropolitan area (4 x 25 = 100)
urban 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

Applying this cluster distribution to the entire population (all index ages and age groups) the total sample is 4x300 = 1200. Using such a sample, comparison can then be made 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. As a general guideline for basic oral health surveys for planning, monitoring and evaluating oral care services, this pathfinder approach to sample design and selection is recommended.


Last updated by Gisela Ladda Tayanin