Sampling

Question 1

population

Answer 1

everyone fitting criteria
clearly defined

Question 2

sample

Answer 2

subset of pop
representative of whole pop
minimise sampling error and variability

Question 3

characteristics of ideal sample

Answer 3

representative
independence
adequacy
homogeneity

Question 4

2 categories of sampling methods

Answer 4

probability sampling (random)
non probability sampling

Question 5

probability sampling

Answer 5

simple random sampling
stratifed
systematic
multistage

Question 6

non probability sampling

Answer 6

judgment or deliberate
convenience
snowball
quota

Question 7

probability sampling advantages

Answer 7

requires detailed info to be effective
estimates which can be measured precisely and unbiased
can evaluate relative effectiveness

Question 8

probability sampling disadvantages

Answer 8

high degree of skill
requires time to plan
costs are higher

Question 9

simple random sample

Answer 9

random number generated

Question 10

random sample +ve and -ve

Answer 10

+
simple
no bias
representative
easy to detect errors
-
lack of control

Question 11

stratified

Answer 11

ratio of number of items to be selected from each strata should be the same as the total number of the units in the strata bearing the units of entire pop

Question 12

types of stratified

Answer 12

proportionate
disproportionate
stratified weighted

Question 13

stratified + and -

Answer 13

+
greater control
representative
can replace units
-
bias
hard to achieve proportion
hard to make representative
hard to place cases under level

Question 14

stratified + and -

Answer 14

+
greater control
representative
can replace units
-
bias
hard to achieve proportion
hard to make representative
hard to place cases under level

Question 15

systematic + and -

Answer 15

+
Simple to draw
variance are smaller
reduces variability
-
interval related to ordering may increase variability
estimates of error likely

Question 16

multistage sample

Answer 16

random sampling in each sampling stages where there are more than 2

Question 17

multistage sample + and -

Answer 17

+
complete list of pop not needed
lower cost of travel f geographically defined
-
errors likely to be large in simple or systematic
errors increase as no. of selected sample units decrease

Question 18

non probability sampling methods

Answer 18

do not provide every item in pop with equal chance
partially subjective

Question 19

judgment sampling

Answer 19

choice of sample depends primarily on judgment of researcher

Question 20

judgment sampling + and -

Answer 20

+
enables inclusion of important units
obtains more representative when looking at unknown traits
practical
-
risk of including researchers needs
can objectively evaluate reliability

Question 21

convenience sample

Answer 21

when population not well defined
sampling unit not clear
complete list not available

Question 22

snowball sample

Answer 22

research contacts with small no. of ppl who establish new connections

Question 23

snowball sample problems

Answer 23

no accessible sample frame
unrepresentative

Question 24

quota sample

Answer 24

1. classify pop into types that assumed to be relevant
2. determine proportion of population falling into each type
3. setting of quotas for each interviewer who has responsibility of selecting ppl so contains correct proportion

Question 25

quota sample + and -

Answer 25

+
low costs to prepare
some stratification effect
-
bias of investigator
errors cannot be estimated by stat procedures

Question 26

factors affecting reliability

Answer 26

size
representativeness
parallel sampling (another sample for testing)
homogeneity of samples (have all same features)
unbiased selection

Question 27

3 types of errors

Answer 27

sampling variability
sampling error
non sampling error

Question 28

sampling variability

Answer 28

different samples from the same pop don’t always produce same mean and sd

Question 29

sampling error

Answer 29

mean of sample won’t be same as mean of pop

Question 30

non sampling error

Answer 30

eg
questions asked badly
poor measurements
errors in recording