Lecture 7 (Sampling Notes)

Question 1

the process of selecting a representative portion of a population

Answer 1

Sampling

Question 2

representative means __

Answer 2

• reproduces the important characteristics of the population
• Uses the EPSEM method (Equal Probability of Selection Method)

Question 3

uncertainty that arises from working with a sample rather than the entire population

Answer 3

Sampling error

Question 4

A large sample is more likely to include a true cross-section of the population (t or f)

Answer 4

t

Question 5

A large sample is more likely to include a true cross-section of the population (t or f)

Answer 5

t

Question 6

When the procedures used to select the sample tend to favor the inclusion of individuals in the population with certain population characteristics

Answer 6

Sampling bias

Question 7

why sample?

Answer 7

• It is not necessary to take a complete census
• Sampling requires less costs, time, and effort
• The population may be infinite
• The population may be empirically definable, but not practically available
• Sample also allows for a wider scope and more in-depth study

Question 8

sampling process

Answer 8

Define the population
Construct the sampling frame
Select the sampling design
specify the info to be collected
collect data

Question 9

difference between descriptive and inferential

Answer 9

inferential draw conclusion/generalize a larger population

Question 10

the population to whom a researcher wishes to generate the results of a study

Answer 10

target

Question 11

the smaller portion of the target population to whom the researcher actually has access to

Answer 11

study

Question 12

the group of people selected to be part of the study

Answer 12

sample

Question 13

ordered list of sampling units representing the population from which the sample will be drawn
- it must include all individuals in the population (it must be exhaustive)
- each individual element of the population must appear once and only once

Answer 13

Sampling frame

Question 14

procedure used to select individuals from the list of samples

Answer 14

Sampling design

Question 15

extended test of data collection procedures to be used in a study in advance of the main data collection
- to check instruments, data loggers and all other logistics
- sometimes reveal deficiencies

Answer 15

pilot or pre-test

Question 16

the probability of any individual member of the population being picked for the sample can be specified

Answer 16

probability sampling

Question 17

advantage of probability sampling

Answer 17

sampling error can be calculated

Question 18

each element in the pop. has an equal probability of being selected as a sample

Answer 18

SRS/Simple Random Sampling

Question 19

adv and disadv of SRS

Answer 19

ADVANTAGE: simple and easy to apply when the pop. is small
DISADVANTAGE: cumbersome for large pop., not the most statistically efficient method
- Possible not to get a good representation due to “luck” of the draw
- randomness does not guarantee representativeness

Question 20

every kth element starting from a randomly chosen point

Answer 20

Systematic Random Sampling

Question 21

subset of the population that has at least one common attribute

Answer 21

Stratum

Question 22

Sample is obtained by forming classes, or strata, in the population and then selecting a simple random sample from each

Answer 22

Stratified Random Sampling

Question 23

adv and disadv of Stratified Random Sampling

Answer 23

ADVANTAGES: reduces sampling error, decreasing the likelihood of obtaining an unrepresentative sample
- Assumes representation of key subgroups
DISADVANTAGES: still cannot guarantee representativeness if the sampling interval corresponds to a pattern

Question 24

adv and disadv of stratified random sampling

Answer 24

ADVANTAGES: reduces sampling error, decreasing the likelihood of obtaining an unrepresentative sample
Assumes representation of key subgroups of the pop.
DISADVANTAGE
May require additional prior info about the population and strata

Question 25

proportionate allocation vs optimum allocation

Answer 25

PA = Size of sample selected from each stratum is proportional to the size of the stratum in the entire population - ADVANTAGE: composition of the sample in terms of its representativeness can be considered OA = proportionality of the sample size to the stratum is not considered - LIMITATION: cannot generalize directly to the population without applying weights

Question 26

- The population is first divided into mutually exclusive and exhaustive clusters, then selecting a simple random sample from each. - Clusters should be Small scale representation of the population - Ideally, each cluster should be internally heterogeneous

Answer 26

Cluster Sampling

Question 27

adv and disadv of cluster sampling

Answer 27

ADVANTAGES: efficient when the population to be sampled is geographically dispersed over a large area - Restricting the sampling to a small number of clusters DISADVANTAGES: Often gives poor results; sample error is higher

Question 28

sampling is done in a hierarchy of stages with the other four techniques applied in various combinations

Answer 28

Multi-stage Sampling

Question 29

adv and disadv of Multi-stage Sampling

Answer 29

ADVANTAGES: convenient and efficient DISADVANTAGES: higher sample error - Entails much planning before sampling is done

Question 30

sample are selected in some non-random manner

Answer 30

non-probability / non random sampling

Question 31

adv and disdv of non-probability / non random sampling

Answer 31

ADVANTAGE: useful when time is limited, a sampling (frame) not available, budget is tight DISADVANTAGE: cannot generalize the general population

Question 32

only convenient or accessible, members of the population are selected - Useful for pilot or pre-testing

Answer 32

Convenience sampling

Question 33

Personal judgment is used to decide which individuals of a population are to be included in the sample - Useful when there is a limited number of people that have expertise in the area being studied - likely to overweigh samples that are more readily accessible

Answer 33

Purposeful or Judgemental sampling

Question 34

an attempt to obtain a representative sample by acquiring quotas from given sample

Answer 34

Quota sampling

Question 35

Sample consists of individuals who self-select from the population, rarely representative - Individuals are usually more motivated or have a higher interest in the topic

Answer 35

Voluntary sampling

Question 36

respondents are accumulated by using each individual as an informant or source of sample

Answer 36

snowball sampling

Question 37

The probability distribution of a sample stat/sampling distribution

Answer 37

CLT

Question 38

Taking all possible samples of size n from a population, calculating the statistic for each sample, and drawing the distribution of those values

Answer 38

CLT

Question 39

adv and disadv of systematic RS

Answer 39

ADVANTAGES: simpler than SRS, gives a good spread across the pop. DISADVANTAGES: still cannot guarantee representativeness if the sampling interval corresponds to a pattern