SOWK 6003 Social Work Research

Week 8 Sampling

By Dr. Paul Wong

Purposes of Research

1. Exploration

2. Description

3. Explanation

4. Evaluation

5. Multiple purposes

Sampling

• Population is the entire group

• Sample is just a part of the population

• Sampling Frame is a list that hopefully covers all the elements in the population that we are sampling from. (e.g. membership list, census data, household list, telephone number etc.)

Considerations in Sampling

Sampling error

Sample size

Variability in the population

Probability Sampling Vs Non-Probability Sampling

Probability Sampling - A method used in research whereby any person in the population has a specified probability of being included in the sample.

Four general strategies:

1. Simple random sampling (SRS): that specifies that each person in a population has the same chance of being included in a sample as every other person.

2. Systematic sampling: by creating a list of every element in the population and selecting every nth member from the population

3. Stratified random sampling: a process of sampling in which groups of interest (e.g. gender, age, religious affiliations, years of study etc.) are identified, then participants are selected at random from these groups.

4. Cluster sampling: a process of sampling in which a number of groups (or clusters) are identified in a population, then some clusters are randomly selected for participation in a research project.

Non-probability Sampling

more commonly used in psychology and social work research

Four strategies:

1. Convenience sampling: involves using whatever participants can conveniently be studied. It is also called availability sampling, or accidental sampling.

2. Quota sampling: subgroups are identified and a specified number of individuals from each group are included in the research

3. Purposive (Judgmental) sampling: participants are selected because of some desirable characteristics.

4. Snowball: participant is selected who then identifies further participants that he or she knows, often useful for finding hidden populations.

Multi-stage Design in Sampling

• Cluster sampling + simple random sampling

• Cluster sampling + stratified random sampling

• Cluster sampling + cluster sampling + simple random sampling

Note: The increase number of stage = increase number of sampling error

Sampling in Qualitative Research Methods

Non-probability Sampling: sampling is not guided by the systematic errors in the coverage of a population.

Criterion based or purposive sampling: the sample units are chosen because they have particular features or characteristics which will enable detailed exploration and understanding of the central themes and puzzles which the researcher wishes to study.

• Homogenous samples• Heterogeneous samples• Extreme case or deviant sampling• Intensity sampling• Typical case sampling• Stratified sampling• Critical case sampling

Sample Size

Determinants for sample size:

• heterogeneity of the population

• number of selection criteria

• extent to which nesting of criteria is needed

• group of special interest that require intensive study

• multiple samples within one study

• type of data collection methods

• budget and resources available

Choices of samples

Individual

- preferably on issue on intra-psychic level (cognitive and emotional) or personalized

- the topic is highly sensitive

- the problem is unique with small population pool

- early stage of exploratory research or want to confine the topic with negative cases or critical cases

Families

- preferably on issue of families, or interpersonal one

- on the same experience in a family

- ethical consideration : children as informants with the parents

Groups

- experience common to a group of peoples, thus larger sample pool

- sometimes used in marketing research, generation of items for questionnaires or for policy formulation

- researchers are inclined to support the social constructive view

- usually at early stage of streamlining the topic or end stage for discussion of controversial issues.

- E.g. focus group, Delphi technique

Triangulation

• is a comparative strategy for examining data that strengthens qualitative and multi-method research

• Describes the use of multiple approaches to the study of a phenomenon.

In class activity 1

Articles Critique:

1) Socio-economic and psychological correlates ofsuicidality among Hong Kong working-age

adults: results from a population-based survey