HOC14:Samples

Question 1

what is sampling

Answer 1

sampling is about selecting the right individuals , objects , or events as representatives for the entire population -> we are interested in the characteristics of the population we sample from

Question 2

what do we not just use the entire population and instead sample

Answer 2

because it is :
- practically impossible
- time-consuming and costly
- not always known
- not always reliable results

Question 3

define population

Answer 3

entire group of people, events, things -> ex. study on advertising by computer firms in Brussels: all 100 computer firms in Brussels

Question 4

define what an element means

Answer 4

single member or subject of the population

Question 5

define what a sample means

Answer 5

a subset or subgroup of the population -> some members selected from it
-> ex. 30 computer firms drawn from the population

Question 6

define what sampling unit means

Answer 6

element available for sample selection
-> ex. firm, person, student, organization ( not the same respondent) -> ex. firm = sampling unit , & general manager = respondent

Question 7

what does accuracy and precision mean in sampling

Answer 7

a sample must be valid by representing the characteristics of the population -> in which accuracy and precision play a key role :
-> Accuracy of the sample means ensuring the lowest degree of sample bias

Question 8

how can accuracy be achieved in sampling

Answer 8

by having sufficient elements in the sample such that :
- values of sample elements are close to population values
-overestimation or underestimation avoided
- non-response avoided (ex. sending out surveys -> cant make sure that responses are not biased)

Question 9

what is sample data and population values mean in relation to sampling

Answer 9

a sample must also be valid by representing the characteristics of the population -> this can be done through precision
-> precision of an estimate means avoiding sampling error = ( the result of the sample should be close enough to the population)

Question 10

what does sampling process mean

Answer 10

Relation of Sample to Population:
Sampling units provide responses.
Responses → Sample statistics → Population parameters.
Sampling Process Overview

Question 11

what are the factors influencing what sample size is needed?

Answer 11

*Factors:
Greater dispersion in the population requires a larger sample.
Higher desired precision necessitates a larger sample.
More sub-groups of interest in the sample require a larger sample.
If the sample size is > 5% of the population, it may be reduced without sacrificing precision.

*Key Principle:

Selecting a sufficient number of the right elements from the population enables the generalization of properties to the entire population.

Question 12

what are the major steps of the sampling process?

Answer 12

1. define the population
   2.determine the sampling frame
   3.determine the sampling design
2. determine the appropriate size
   5.execute the sampling process

Question 13

what does the step of defining the population mean

Answer 13

research objective and scope : key in defining the target population

Question 15

what does the step of determining the sampling frame mean

Answer 15

• list items from which sample is drawn = population ( or sub-set) list
• names and addresses of people in the population
• ideally , sampling frame is target population , but in practice rarely the case

Question 16

what does the step of determining the sampling design mean

Answer 16

*Probability (or random) sampling is favored for representativeness and generalizability.

*Non-probability sampling is more practical when time is limited or generalizability is less important.

Question 17

what does the step of determining the appropriate sample size mean

Answer 17

Difficult decision -> rule of thumb: 30-500.

Factors affecting size decisions include:
research objective,
desired precision,
population dispersion,
cost, and time constraints.
size of the population

*Myth: A larger sample is not always more representative; it depends on the factors mentioned.

Question 18

what are the two different approaches to probability sampling

Answer 18

unrestricted or simple random sampling
restricted or complex probability sampling

Question 19

what does unrestricted or simple random sampling mean in probability sampling approaches?

Answer 19

*Definition:
Every element in the population has a known and equal chance of being selected as a subject.
Selection is individual and direct from the population.

*Characteristics:
Population and sample distributions are similar.
Least bias and highest generalizability.
However, it is time-consuming and costly.
Requires a population list (serving as a sampling frame), which is often not available.

Question 20

what is restricted or complex probability sampling?

Answer 20

Involves a more controlled and specific approach than simple random sampling.
Different techniques are used to ensure representation while addressing practical constraints.
includes :
-stratified random sampling
-proportionate and disproportionate stratified random sampling
-cluster sampling
-particular case: destructive sampling

Question 21

what is stratified random sampling * in restricted or complex sampling

Answer 21

Population divided into subgroups (strata) based on certain characteristics.
Random samples are then taken from each stratum.
Ensures representation from various subgroups.

Question 22

what does cluster sampling mean

Answer 22

• used when size of population is very large
• population divided into smaller groups ( clusters) , samples are drawn out at random from these groups
  
  • ex: population at city level → take sample at district level , with same features as population = area sampling

Question 23

what does a particular case mean in restricted probability sampling

Answer 23

• a technique in which samples are destroyed → population is changed in the random sampling process
  
  • ex. during the test for quality control of light bulbs, car crash tests

Question 24

what are the different approaches to non-probability sampling

Answer 24

quota sampling
convenience sampling
purposive sampling
snowball sampling

Question 25

what is quota sampling?

Answer 25

Quotas in the form of percentages are established for different classes of population ( selection criteria: gender , age, nationality…) to make the sample more representative → ex. street-survey of people

Question 26

what is convenience sampling?

Answer 26

data collected from members of the population who are conveniently available to provide it => easily accessible

Question 27

what is purposive sampling?

Answer 27

after defining the criteria ( characteristics of the population and objective of the study) → you search for people who meet the criteria

Question 28

what is snowball sampling

Answer 28

• recruiting participants via the other participants in the network
• when participants are difficult to find or identify

Question 29

what is a theoretical sampling?

Answer 29

• the process of repeated data collection for generating theory ( see Grounded Theory) → up till the point of saturation
• characteristics of the sample ( and population only become clear at the end of the sampling process