4. Type of Sampling

Question 1

characteristics of random sampling?

Answer 1

there’s a calculable probability of being selected; if 1000 students out of 10000 are picked then that means 1/10

• widely adopted by leading research bodies
• Only completely objective method of sampling,(some groups will be avoided when going for something more methodical) non-biased
• avoids interview bias. Those choosing the researchers can’t pick their preferred ones

NB - very few sampling frames available

• there’s a possibility of the frame being out of date
• considerable delays in completing surveys
• possible geographical dispersion of informants
• “callbacks” increase cost/ cause delay

Question 2

what random sampling techniques are there?

Answer 2

• simple random
• systematic or quasi-random
• stratified random - some aged 20-25 some 30+ (sport students & business students)
• cluster - pick on one particular area rather than across the country because results are likely to be similar (it’s not always viable to go everywhere as its time consuming and more costly and pointless)
• multi-stage - 9 regions in the UK pick one at random, THEN, start collecting counties, the towns
• replicated
• master
• multi-phase - from 10000 we select 1000 ask them some questions the 50 much more detailed questions than before

Question 3

Name some characteristics of Non- Random Sampling

Answer 3

-Also known as “judgement”, “purposive”, or “quota”
Individual units in population do not have known chance of being selected
-Selection of sample depends on human choice
-Type of stratified sample (eg. age, sex, social class etc.)
-Biases arising from interviewers’ subjective choice of informants - controlled to some extent by quota controls.
-Interviewers allocated specific numbers of various types of informants (eg. age, sex, social class etc.)
-Quotas of types of informants devised in proportion to their importance related to survey objectives

Question 4

Advantages of Quota Sampling

Answer 4

• speed - no need for call-back
• cost - much less than for random
• simplicity - no need for sampling frames
• accuracy - if expertly controlled

Question 5

Disadvantages of Quota Sampling

Answer 5

• not representative (eg. occupation/education level).
• Some interviewer bias in respondent selection
• some bias due to time of day, and location

Question 6

Why are quota controls used?

Answer 6

-Improve quality of quota sampling
-Need to identify relevant quota factors (eg. age, sex, class, religion etc.)
-Allocate proportions of types of informants according to actual distribution in population
-Two broad types of quota controls:
1. “independent” quota results in biased
selection
2. “interrelated” quota is far more reliable and
controls types of respondents interviewed

Question 7

What is snowball sampling?

Answer 7

• Sometimes referred to as network sampling
• Used if a list or sampling frame not available or if sample difficult to find, for example a low incidence or low visibility group.
• May end up with a samplemade up of people with similar characteristics.
• No control over respondents
• No indication of population

Question 8

What Socio-economic classifications are there in the UK?

Answer 8

official:
-ONS
-International Standard Classification of Occupations 
professional:
-National readership survey
-Pan European Social grading

Question 9

National Statistics Socio-economic Classification

Answer 9

-Higher Managerial and professional occupation (21%)
1A Employers and managers in large organisations (9%)
Company directors, senior police officers, senior local government officers, bank managers
1B Higher professionals (12%)
Doctors, lawyers, dentists, higher civil servants, professors, professional engineers, teachers, airline pilots, social workers, librarians
-Lower managerial and associate professionals (17%)
Police sergeants and constables, prison service officers, firemen, journalists, nurses, physiotherapists, actors, musicians, professional sportsmen, lower ranking civil servants
-Intermediate occupations (14%)
Precision instrument makers, computer engineers, dental technicians, secretaries/Pas, airline flight attendants, driving instructors

Question 10

What are the International Standard Classification of Occupations?

Answer 10

Major Group 0/1 Professional, technical and related workers
Major Group 2 Administrative and managerial workers
Major Group 3 Clerical and related workers
Major Group 4 Sales workers
Major Group 5 Service workers
Major Group 6 Agricultural, animal husbandry and forestry workers, fishermen and hunters
Major Group 7/8/9 Production and related workers, transport equipment operators and labourers
Major Group X Workers not classified by occupation
Armed Forces Members of the armed forces

Question 11

What are the key steps for sample design

Answer 11

1. Define closely population to be surveyed
2. Decide whether census feasible or sample survey suitable. If latter, then decide on ‘random’ or ‘quota’
3. Decide on number of sampling stages (multi-stage sampling often used).
4. Define stratification factors relevant to survey objectives