ORGANISING AN ORAL HEALTH SURVEY

WHO ORAL HEALTH SURVEYS Basic Methods

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What is an Oral Health Survey?

A survey is a system for collecting information to

describe, compare, monitor changes in oral health

status, knowledge, attitudes, and behaviour.

Oral Health Surveys.

• Planning the survey

• Writing a protocol

• Obtaining resources

• Collecting data

• Analysing data

• Reporting the results

ORAL HEALTH SURVEYS

Surveys to determine the oral health status and treatment

needs of comm on unities and populations are an essential

part of the duties of chief dental officers and other

administrators responsible for oral health care services

(WHO, 1997).

Use of Oral Health Surveys

• To determine the extent to which existing oral health

services are coping with the current need for care.

• To determine the nature and extent of required preventive,

curative and restorative services.

• To determine the resources needed to establish, maintain,

expand or reduce an oral health care programme, including

an estimate of the number and type of personnel required.

Key features of a good survey:

• Specific objectives and straightforward research questions. Clear

definition of the population.

• Appropriate size of the sample.

• Sound sampling procedures.

• Reliable and valid survey instruments.

• Trained and calibrated examiners and interviewers.

• Appropriate examination area and good cross-infection control.

• Ensure emergency care and referral.

• Appropriate data analysis.

• Accurate reporting of survey results. Reasonable resources.

• Pilot study.

• Detailed survey protocol.

Outline for a Survey Protocol

Title

Background

Data and information required

Objectives

Population to be studied

Sample size

Sample selection criteria

Survey procedures

Data collectionand instruments

Data analysis plans

Reporting plans

Research team

Facilities,equipment, supplies

Budget

Time schedule

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

The manual provides:

• A description of diagnostic criteria that can be readily

understood and applied in all countries.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

The manual provides:

• Information on means of obtaining practical

assistance for planning and implementing surveys,

summarising data and analysing results.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

Aims of the manual:

To provide a systematic approach to the collection and

reporting of data on oral diseases and conditions.

To ensure that data collected in a wide range of

environments are comparable.

To encourage oral health administrators in all countries

to make standard measurements of oral diseases and

conditions as a basis for planning oral health care

services.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

The manual provides:

• Guidelines on a practical and economic sample design

suitable for assessing oral diseases and treatment needs for

planning and monitoring oral health services.

Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva,

WHO.

The manual was not designed to collect information about

etiological factors affecting disease distribution or severity, or

to test the clinical effectiveness of different preventive or care

procedures.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

• Pathfinder method:

-a stratified cluster sampling technique, which aims to

include appropriate number of subjects selected from the

most important population subgroups likely to have

differing disease levels.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

• Index Ages and Age Groups:

5 years

12 years

15 years

35-44 years

65-74 years

Oral Health Surveys: Basic Methods.

4th ed, 1997. Geneva, WHO.

Number of subjects per site:

Low Level of Disease = 25

Moderate/ High Level of Disease = 40-50

Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva,

WHO.

• Pilot Survey includes only the most important subgroups in

the population and only one or two index ages or age groups.

• National Survey incorporates sufficient examination sites to

cover all important subgroups of the population and at least

three of the index ages or age groups.

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

Sample Size for each Index Age:

- Number of subjects per site: 25-50.

- Number of sites: 10-15

- Total number of subjects: 250-750

Oral Health Surveys: Basic Methods. 4th ed, 1997.

Geneva, WHO.

• Guide for estimating the level of disease:

• Low Level of disease

Prevalence < 80%

• Moderate Level of disease

Prevalence < 95% and> 80%

• High Level of disease

Prevalence > 95%

Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva,

WHO.

• Guide for choosing the sampling sites:

• Administrative divisions of the country - The capital city

- Main urban centres

- Small towns

- Rural areas

SAMPLE SIZE FOR POPULATION SURVEYS

· Population surveys aim to estimate a quantity of interest

with a specified precision.

· The main idea behind the sample size calculation is to

have a high precision to estimate a quantity of interest

from sample population.

Formula for calculating sample size for

population surveys:

· Sample size = p(1 - p)/e2

p = Prevalence of disease in the population

e = Required size of standard error

Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva,

WHO.

Sample selection and sample size for one index age:

• Urban:

_ Capital City 4 sites (4 x 25 = 100)

- 2 Large Towns 4 sites (2 x 2 x 25 = 100)

• Rural:

- 4 Villages 4 sites (4 x 25 = 100)

- Total: 12 sites (12 x 25= 300)

SAMPLE SIZE FOR POPULATION SURVEYS

· A simple method to calculate sample size for a

population survey is to use the formula for single

proportions.

· Outcome variable must be measured in a dichotomous

scale.

EXAMPLE

Suppose that we are planning a population survey to

assess dental caries experience among 12 old children

living in an affluent town with 1.8 million people.

There is no information on previous published data

reporting the prevalence of dental caries. Let's

calculate the required sample size.

SAMPLING METHODS FOR POPULATION SURVEYS

• The major principle which underlies the sampling criteria is

to avoid bias in the selection procedure.

Simple random sampling method:

To compile a list of all the individuals in a population and to

number them.

- sampling frame

• To select the required number of individual at random, i.e.,

- draw from labelled cards

- table of random numbers

- computer-generated random numbers

Systematic sampling method:

To compile a list of all the individuals in a population and

to number them (sampling frame) .

•To calculate the sample fraction .

•To choose at random a starting point in the list .

•To select the required sample size taking individuals at

regular intervals down the list .

Random Sampling

The selection of a study population (sample) must gives

to each member of the target population the same chance

of being selected .

•The most common method of selection of a study

population is the simple random sampling .

Systematic Sampling

For convenience, the selection of a study population

may be carried out systematically rather than

randomly.

SAMPLING METHODS FOR POPULA TION

SURVEYS

• There are many situations in which a simple random

sampling or a systematic sampling method is not

appropriated and more complex sampling scheme is

necessary.

SAMPLING METHODS FOR POPULATION

SURVEYS

Situations when a more complex sampling scheme is

necessary:

A sampling frame does not already exist and it would be too

costly or impracticable to compile one.

The population is spread overa wide area and the travel costs

and time involved in covering the whole area are

prohibitive.

The population consists of quite distinct subgroups.

Stratified sampling method

To define the strata of interest in a population, i.e., age

groups, sex, social class, regions of a country or areas of

a town.

• To compile a list of all individuals in each stratum.

• To select the required number ofindividuals from each

stratum. A simple random sampling ora systematic

sampling method maybe used.

Cluster sampling method

To define the stages to be considered using the hierarchical

structure of a population, Le., schools and then school

children.

• To compile a list of first-stage units.

• To select at random or systematically the required number of

first-stage units.

• To include all individuals in the selected first stage units.

SAMPLING METHODS FOR POPULATION

SURVEYS

• Other sampling methods are: -Stratified sampling

-Multi-stage sampling

-Cluster sampling

Sampling methods may be used alone or in

combination.

Multi stage sampling method

To define the stages to be considered using the hierarchical

structure of a population, i.e., schools and then school-

children

To compile a list of first-stage units.

To select at random or systematically the required number of

first-stage units.

To compile a list of second-stage units.

To select at random or systematically the required number of

individuals from the second-stage units selected.

Reliability and Validity of an Oral Health Survey Data

Training and Calibrating of Examiners:

• To ensure uniform interpretation, understanding and

application by all examiners of the codes and criteria for

the various diseases and conditions to be observed and

recorded.

• To ensure that each examiner can examine consistently.

Pilot Study

• Test organisation of the survey

• Carry out a calibration and training of personnel

(examiners, organising and recording clerks)

• Estimate the level of disease

• Identify problems

• Adjust the survey design