STUDY POPULATION SAMPLE/INCLUSION AND EXCLUSION

CRITERIA

PresentersAnne Obondo/Dennis Donovan

Objectives

We expect that at the end of this presentation, you will be able to:

Define your population sample

State your inclusion and exclusion criteria.

Population Generally:

Population denotes the number of people within a given boundary

• www.stats.gla.ac.uk.

In research,1. Target population

Refers the entire group of subjects or participants you wish to generalize the study findings

For example, All institutionalized alcoholics Or all university students Or Slum dwellers who abuse alcohol

2. Accessible population Is the subset of the target population and

is also known as the study population.

May be limited to region, state, city, county, or institution

For example, All institutionalized alcoholics in Nairobi

county

Or all university students in Nairobi county

Sample and sample frame

Sample Is a subset of the population and a

typical representative of the larger group or population.

Sample frame Is a list of all the participants in the

population from which the sample is drawn

www.stats.gla.ac.uk

For example, For example, if you study is “assessment

of the effectiveness of counseling services in Nairobi”

You need a list of all counselling clinics from which you will draw your study sample

In opinion polls – electoral register and telephone directory.

Gives the participants equal opportunity of being selected as subjects or participants

Effective sample frame

Has information about participants. Is organized in a logical and systematic

fashion Include every participant of the population No elements from outside the population

of interest are present The data is 'up-to-date‘ ( Tunner A. G.,2012)

Illustrative Diagram – Population sample

Relationship between population and sample

Population is the entire group

Sample is a subset of the population. Before sampling it is important to

carefully and correctly define the population

Sample is used to make generalizations about a population

Sample must be good size to warrant statistical analysis

The more diverse the population the larger the sample.

Sample is drawn from the population and the population takes conclusions from the results obtained from the sample.

Research triad

Why sample your population

Makes study population easily accessible since it is impossible to study the whole population.

Generalization of the findings to the target population can be adequately made.

Makes it easy for statistical data analysis However, in qualitative studies you may

not need to sample your population

Examples

Psychiatric morbidity among adult HIV/AIDS patients attending a comprehensive care centre at a city council clinic in Nairobi.

Target population

Study population

Problems in study population sample

1. Bias in Selection

Sources of biasOmitting people in hard to reach

groups Replacing selected individuals with

others, because they are in accessibleUse of outdated list as sample frame

When population sample is not characteristic of the population.

Some members of the population are not included in the frame

The non-members of the population are included in the frame. (Leslie Kish, 1995).

2. Being too ambitious

Some points to consider Consider whether your study is

quantitative or qualitative. Define your population from which the

sample is to be drawn. Consider sample frame with a appropriate

contact information Will the population that you want to study

meet your objectives

Is my study population accessible? Is my study population representative of

the target population? Is it diverse that I can make inferences.

Inclusion and Exclusion Criteria Inclusion criteria are characteristics that the

prospective subjects must have if they are to be included in the study.

Exclusion criteria are those characteristics that disqualify prospective subjects from inclusion in the study.

http://learn.yale.edu/hsp/module_5/3a_guidance.asp

Inclusion and exclusion criteria may include factors such as age, gender, race, ethnicity, type and stage of disease, the subject’s previous treatment history, and the presence or absence (as in the case of the “healthy” or “control” subject) of other medical, psychosocial, or emotional conditions.

Defining inclusion and exclusion criteria increases the likelihood of producing reliable and reproducible results, minimizes the likelihood of harm to the subjects, and guards against exploitation of vulnerable persons

http://learn.yale.edu/hsp/module_5/3a_guidance.asp

General Population of Interest

Inclusion Criteria Exclusion Criteria

Sample

SMART-ED Inclusion Criteria 18 years old or older Seeking medical treatment at the ED Had adequate English language proficiency Were capable of providing informed consent Had a score of 3 or greater on the 10-item

Drug Abuse Screening Test (DAST-10) Reported at least 1 day of drug use in the 30

days prior to screening Were willing to participate in the protocol Had access to a telephone.

SMART-ED Exclusion Criteria Prisoners or in police custody Currently engaged in or actively seeking

addiction treatment Resided more than 50 miles from the follow-

up location Were unable to provide sufficient contact

information Had already participated in the study.

Screening and Randomization

• 4,005 participants endorsed past-30d drug use (27% of TADs).

• Of these, 1,285 were randomized (32% of drug users).

• Probably most of those not randomized were excluded because they did not meet DAST ≥ 3 criterion.

24

Pre-Screened: 20762

Screened: 15224

Randomized: 1285(427 BIB, 427 SAR, 431

MSO)

3-mo f/u: 1026

6-mo f/u: 1107

12-mo f/u: 1043

1 analysis: 113926

References

Turner, Anthony G. "Sampling frames and master samples“. United Nations Secretariat, 12/11/2012.

Leslie Kish (1995). Survey sampling. Wiley. ISBN 978-0-471-10949-5. Retrieved 11 January 2011. [