Presentation on theme: "ORGANISING AN ORAL HEALTH SURVEY WHO ORAL HEALTH SURVEYS Basic Methods"— Presentation transcript:
1 ORGANISING AN ORAL HEALTH SURVEY WHO ORAL HEALTH SURVEYS Basic Methods دکتر سید ابراهیم جباری فر( (Dr. jabarifar تاریخ : 1388 / 2010دانشیار دانشگاه علوم پزشکی اصفهان بخش دندانپزشکی جامعه نگر
2 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.
3 Oral Health Surveys.Planning the survey• Writing a protocol• Obtaining resources• Collecting data• Analysing data• Reporting the results
4 ORAL HEALTH SURVEYSSurveys 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).
5 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.
6 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.
7 Outline for a Survey Protocol TitleBackgroundData and information requiredObjectivesPopulation to be studiedSample sizeSample selection criteriaSurvey proceduresData collectionand instrumentsData analysis plansReporting plansResearch team Facilities,equipment, suppliesBudgetTime schedule
8 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.
9 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.
10 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.
11 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.
12 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.
13 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.
14 Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva, WHO. • Index Ages and Age Groups:5 years12 years15 years35-44 years65-74 years
15 Oral Health Surveys: Basic Methods. 4th ed, Geneva, WHO.Number of subjects per site:Low Level of Disease = 25Moderate/ High Level of Disease = 40-50
16 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.
17 Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva, WHO. Sample Size for each Index Age:- Number of subjects per site:- Number of sites:- Total number of subjects:
18 Oral Health Surveys: Basic Methods. 4th ed, 1997. Geneva, WHO. • Guide for estimating the level of disease:• Low Level of diseasePrevalence < 80%• Moderate Level of diseasePrevalence < 95% and> 80%• High Level of diseasePrevalence > 95%
19 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
20 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.
21 Formula for calculating sample size for population surveys: · Sample size = p(1 - p)/e2p = Prevalence of disease in the populatione = Required size of standard error
22 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: sites (12 x 25= 300)
23 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.
24 EXAMPLESuppose 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.
25 SAMPLING METHODS FOR POPULATION SURVEYS • The major principle which underlies the sampling criteria is to avoid bias in the selection procedure.
26 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
27 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.
28 Random SamplingThe 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.
29 Systematic SamplingFor convenience, the selection of a study population may be carried out systematically rather than randomly.
30 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.
31 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.
32 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.
33 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.
34 SAMPLING METHODS FOR POPULATION SURVEYS • Other sampling methods are: -Stratified sampling-Multi-stage sampling-Cluster samplingSampling methods may be used alone or in combination.
35 Multi stage sampling method To define the stages to be considered using the hierarchical structure of a population, i.e., schools and then school-childrenTo 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.
36 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.
37 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