Ch7 Sampling

Question 1

Qualitative samples

Answer 1

Nonrandom samples - rarely determine the sample size in advance and have limited knowledge about the larger group or population from which the sample is taken

Question 2

Nonprobability - haphazard

Answer 2

get any cases in any manner that is convenientineffective, highly unrepresentative, not recommendedcheap quick but lots of errors worse than no sample

Question 3

Nonprobability - quota

Answer 3

Get preset number of cases in each of several predetermined categories that will reflect the diversity of the population using haphazard methodsimprovement over haphazard - decide how many to have in each category

Question 4

Nonprobability - purposive

Answer 4

get all possible cases that fit particular criteria using various methods

best used in situations in which an expert uses judgment in selecting cases with a specific purpose in mind. - inappropriate to pick the typical schooloften used in explanatory or field research

Question 5

Snowball

Answer 5

get cases using referrals from one or a few cases, then referrals from those cases and so forth.can be used to sample a network sociogram - diagram of circles connected with lines - map that shows the network of social relationships, influence patters or communication paths among a group of people or units

Question 6

Sequential

Answer 6

get cases until there is no additional information or new characteristics

different that purposive, purposive tries to find as many relevant cases as possible until time, financial resources or their energy is exhausted. sequential - researcher continues to gather cases until the amount of new info or diversity of cases is filled - gathered until marginal utility or incremental benefit drops off

Question 7

Purposive sampling appropriate in 3 situations:

Answer 7

1. researcher uses it to select unique cases that are especially informative
2. select members of a difficult to reach, specialized population
3. when a researcher wants to identify particular types of cases for in-depth investigations

Question 8

deviant case sampling

Answer 8

type of purposive sampling researcher seeks cases that differ from the dominant pattern or that differ from the predominant characteristics of other cases variety of techniques to locate cases with different characteristics not represented by the whole - studying unusual especially used by qualitative

Question 9

Theoretical sampling

Answer 9

they continue to collect data until no new information emerges - until reaching theoretical saturation

Question 10

Probability sampling

Answer 10

fundamentally different from nonprobability sampling because it is strongly linked to the science of math and probability draw samples from the same population in a manner so that every case has the same likelihood of being chosen

Question 11

sampling element

Answer 11

unit of analysis or case in a populationcan be a person, group, organization, written document or symbolic message or social action

Question 12

sampling ratio

Answer 12

ratio of the size of the sample to the size of the target population

Question 13

sampling frame

Answer 13

operationalizes a population by developing a specific list that closely approximates all the elements in the population list of cases in a population or the best approximation of it

Question 14

parameter

Answer 14

characteristic of the entire population that is estimated from a sample

Question 15

statistic

Answer 15

a numberical estimate of a population parameter computed from a sample

Question 16

sampling error

Answer 16

how much a sample deviates from being representative of the population

Question 17

margin of error

Answer 17

an estimate about the amount of sampling error that exists in a survey’s results

Question 18

Simple random sampling

Answer 18

a type of random sample in which a researcher creates a sampling frame and uses a pure random process to select cases. each sampling element in the population will have an equal probability of being selected

Question 19

sampling distribution

Answer 19

distribution created by drawing many random samples from the same population

Question 20

sampling distribution of sample means

Answer 20

distribution of sample means created by drawing many random samples from the same population

Question 21

central limit theorem

Answer 21

mathematical relationship stating that whenever many random samples are drawn from a population and plotted, a normal distribution is formed, and the centre of such a distribution for a variable is equal to its population parameter

Question 22

confidence interval

Answer 22

range of values usually a little higher and lower than a specific value found in a sample within which a researcher has specified and high degree of confidence that the population parameter lies

Question 23

stratified sampling

Answer 23

random sample in which the researcher first identifies a set of mutually exclusive and exhaustive cateogies then uses a random selection method to select cases for each category more rep of population than simple random - percentages match population percentages

Question 24

cluster sampling

Answer 24

random sample that uses multiple stages and is often used to cover wide geographic areas in which aggregated units are randomly selected; samples are then drawn from the sampled aggregated units or clustersless expensive but less accurate -must decide on the number of clusters and the number of elements within each clusterstage 1 - random sampling of big clustersstage 2 - random sampling of small clusters within each selected big cluster stage 3 - sampling of elements from within the sampled small clusters

Question 25

probability proportionate to size

Answer 25

an adjustment made in cluster sampling when each cluster does not have the same number of sampling events

Question 26

random digit dialling

Answer 26

a method of randomly selecting cases for telephone interviews that uses all possible telephone numbers as a sampling frame

Question 27

hidden populations

Answer 27

people who engage in clandestine, deviant or concealed activities who are difficult to locate and study

Question 28

How to address question of sample size

Answer 28

make assumptions about the population and use statistical equations about random sampling processes -

conventional or commonly accepted amount

Question 29

principle of sample size

Answer 29

the smaller the population, the bigger the sampling ratio has to be for an accurate sample larger populations permit smaller sampling ratios for equally good samples - as population size grows the returns in accuracy for sample size shrink

Question 30

decision about sample size depends on 3 things

Answer 30

1. degree of accuracy required
2. degree of variability or diversity in the population
3. number of different variables examined simultaneously in data analysis

Question 31

inferential stats

Answer 31

based on a random samplelets a researcher make precise statements about the level of confidence they have in the results of a sample being equal to the population parameter