103 - Lecture 7 & 8 - Sampling 1&2

What is sampling?

It is the process of selecting a sample from a population of interest

What is sampling unit?

It is an observational unit, or a group of observational units, of the population of interest.

What is sampling frame?

It is the complete list of sampling units of a population of interest.

Distinguish between target population and study population

Sampling frame is the target population. However, if some of the sampling units are accessible then these sampling units are excluded from the survey and the rest of the sampling units are known as the study population.

What are the criteria for a sampling frame?

1) each sampling unit has a numerical identifier

2) each sampling unit needs to be found easily. Their contact information should be available.

3) each sampling unit is organized in a logical and systematic manner

4) each sampling unit of the population must be included

5) each sampling unit needs to be included once only

6) no sampling unit from outside the target population can be included

7) list must be updated

What are some of the problems with sampling frames?

1) may be inaccurate

2) may be inadequate

3) may be incomplete

4) may be out of date

What is a representative sample?

A sample that more or less contains the characteristics of the population it’s taken from is said to be representative.

What are the two ways of selecting a sample?

Random sampling and non-random sampling

Describe random sampling

1) Each sampling unit has equal or different probability of being selected

2) There are two types of random sampling: simple random sampling and systematic random sampling.

What is random sampling?

It is the process of selecting a representative sample from a population using the theory of probability.

What is non random sampling?

It is the process of selecting a representative sample from a population using the subjective judgment of the researcher or surveyor. Probability theory IS NOT used here.

Describe non random sampling

1) All sampling units do not have the chance to be selected for the sample

2) Depends on the expertise of the researcher

3) Only used when SRS cannot be carried out due to time constraints and cost.

4) Some types of nonrandom sampling: convenience, quota, purposive, snowball sampling

What are the steps of a sample survey?

1) Objective of the survey

2) Population to be sampled

3) Data to be collected

4) Degree of precision required

5) Mode of data collection

6) Sampling unit and sampling frame

7) Sample selection

8) Pilot survey

9) Organization of filed work

10) Analysis of data

11) Report preparation

What are the methods of data collection?

Direct observation, personal interview, telephone interview, mail inquiry, web inquiry, registration, transcripts from record.