Unit 10 - Introduction to sampling

Question 1

what is the definition of population?

Answer 1

Entire body of units of interest to the decision maker

Question 2

what is the definition of sampling?

Answer 2

Selection of a part of the population for the ultimate purpose of drawing general conclusions about the entire population

Question 3

what is the definition of sampling frame?

Answer 3

a list of all the items in your population. It’s a complete list of everyone or everything you want to study.

Question 4

What are the steps to the sampling process?

Answer 4

1. Define the population
2. Identify the sampling frame
3. Develop a sampling plan
4. Decide on sample size
5. Do the actual selection

Question 5

what is the definition of element?

Answer 5

the object about which or from which the information is desired

Question 6

what is the definition of a sampling unit?

Answer 6

A sampling unit is an element, or a unit containing the element, that is available for selection at some stage of the sampling process

Question 7

what does extent refer to?

Answer 7

the geographic boundaries

Question 8

what are the types of probability sampling?

Answer 8

• Simple Random Sampling
• Systematic Sampling
• Stratified Sampling
• Cluster Sampling

Question 9

what are the types of non-probability sampling?

Answer 9

1 Convenience Sampling: Used to obtain information quickly and inexpensively
2 Judgmental Sampling: “Expert” uses judgment to identify representative samples
3 Snowball Sampling:
• Form of judgmental sampling
• Appropriate when reaching small, specialized populations
• Each respondent, after being interviewed, is asked to identify one or more others in the appropriate group
4 Quota Sampling:
• Minimum number from each specified subgroup in the population
• Often based on demographic data

Question 10

What factors correspond to nonprobability sampling?

Answer 10

• Exploratory research
• Errors are larger
• Population is homogeneous
  Statistical considerations: Unfavourable
  Operational considerations: Favourable

Question 11

What factors correspond to probability sampling?

Answer 11

Conclusive research
Sampling errors are larger
Heterogeneous population
Statistical considerations: Favorable
Operational considerations: Unfavorable

Question 12

Comment on probability sampling

Answer 12

All population members have a known probability of being in the sample

Question 13

Comment on Simple Random Sampling

Answer 13

Each population member, and each possible sample, has equal probability of being selected

Question 14

Comment on Stratified Sampling

Answer 14

The chosen sample is forced to contain units from each of the segments or strata of the population

Question 15

What are the types of stratified sampling?

Answer 15

1. Proportionate Stratified Sampling: Number of objects/sampling units chosen from each group is proportional to number in population
2. Disproportionate Stratified Sampling: Sample size in each group is not proportional to the respective group sizes

Question 16

what are the characteristics of cluster sampling?

Answer 16

• Involves dividing population into subgroups
• Random sample of subgroups/clusters is selected and all members of subgroups are interviewed
• Very cost effective
• Useful when subgroups can be identified that are representative of entire population

Question 17

what are the strengths and weaknesses of simple random sampling (srs)?

Answer 17

strengths: Easily understood; results projectable
weaknesses: Difficult to construct sampling frame; expensive; lower precision; no assurance of representativeness

Question 18

what are the strengths and weaknesses of systematic sampling?

Answer 18

strengths: Can increase representativeness; Easier to implement; Sampling frame not needed
weaknesses: Can decrease representativeness

Question 19

what are the strengths and weaknesses of stratified sampling?

Answer 19

strengths: Includes all important subpopulations; precision
weaknesses: Difficult to select relevant stratification variables; not feasible to stratify on many variables; expensive

Question 20

what are the strengths and weaknesses of cluster sampling?

Answer 20

strengths: easy to implement; cost effective
weaknesses: Imprecise difficult to compute and interpret results

Question 21

how may quota sampling be viewed?

Answer 21

Quota sampling may be viewed as two-stage restricted judgmental sampling.
•The first stage consists of developing control categories, or quotas, of population elements.
•In the second stage, sample elements are selected based on convenience or judgment.

Question 22

what are the approaches to decide on a sample size?

Answer 22

1. Unaided judgment: arbitrary approach
2. All-you-can-afford: cost consideration
3. Average size for sample for similar studies
4. Required size per cell
5. Bayesian statistical method
6. Traditional statistical method: the main focus

Question 23

what information is needed to calculate sample size?

Answer 23

1. Specification of the error (e) that can be allowed.

2. Confidence coefficient

Question 24

how to select fieldworkers?

Answer 24

The researcher should:
•Develop job specifications for the project, taking into account the mode of data collection.
•Decide what characteristics the field workers should have.
•Recruit appropriate individuals.

Question 25

Do you need to train the fieldworkers?

Answer 25

Interviewers should be trained to:
make opening remarks that will convince potential respondents that their participation is important.

• Asking the Questions:

1. Be thoroughly familiar with the questionnaire.
2. Ask the questions in the order in which they appear in the questionnaire.
3. Use the exact wording given in the questionnaire.
4. Read each question slowly.
5. Repeat questions that are not understood.
6. Ask every applicable question.
7. Follow instructions, skip patterns, probe carefully.

Question 26

how to evaluate the fieldworker?

Answer 26

Cost and Time. The interviewers can be compared in terms of the total cost (salary and expenses) per completed interview.

Response Rates. It is important to monitor response rates on a timely basis so that corrective action can be taken if these rates are too low.

Quality of Interviewing. To evaluate interviewers, the supervisor must directly observe the interviewing process.

Quality of Data. The completed questionnaires of each interviewer should be evaluated for the quality of data.