# Ch 7 The Logic Of Sampling

## 35 terms

### element

that unit of which a population is composed and which is selected in a sample. Distinguished from units of analysis, which are used in data analysis

### population

the theoretically specified aggregation of the elements in a study

### study population

the aggregation of elements from which a sample is actually selected

### random selection

a sampling method in which each element has an equal chance of selection independent of any other event in the selection process

### sampling unit

that element or set of elements considered for selection im some stage of sampling

### parameter

the summary description of a given variable in a population

### statistic

the summary description of a variable in a sample, used to estimate a population parameter

### sampling error

the degree of error to be expected in a probability sampling the formula for determining sampling error contains three factors: the parameter, the sample size, and the std. error

### confidence level

the estimated probability that a population parameter lies w/in a given confidence interval. Thus, we might be 95% confident that betw. 35 and 45% of all voters favor Candidate A.

### confidence interval

The range of values w/in which a population parameter is estimated to lie

### sampling frame

that list or quasi list of units composing a population from which a sample is selected. If the sample is to be represetative of the population, it's essential that the sampling frame inculde all members of the population.

### simple random sampling

a type of probability sampling in which the units composing a population are assigned numbers. A set of random numbers is the generated, and the units having thoise numbers are included in the sample

### systematic sampling

a type of probability sampling in which every k-th unit in a list is selected for inclusion in the sample p224

### sampling interval

the standard distance (k) between elements selected from a population for a sample

### sampling ratio

the proportion of elements in the population that are selected to be in a sample

### statification

the groupin of the units composing a population into homogeneous groups before sampling. This procedure, which may be used in conjuction with simple random, systematic, or cluster sampling, improves the representativeness of a sample

### cluster sampling

a multistage sampling in which natural groups are sampled initially, with the members of each selected group being subsampled afterward.

### PPS (probability proportionate to size)

This refers to a type of multistage cluster sample in which clusters are selevted, not with equal probabilities but with probabilities proportionate to their sizes--as measured by the number of units to be subsampled.

### weighting

assigning different weights to cases that were selected into a sample with different probabilities of selection.

### nonprobability sampling

any technique in which samples are selected in some way not suggested by probability theory. Includes subjects as well as purposive (judgmental), snowball, and quota sampling.

### purposive sampling

a type of nonprobability sampling in which the units to be ovserved are selected on the basis of the researcher's judgment about which one will be the most useful or representing. Aka judgemental sampling.

### snowball sampling

a nonprobability-sampling method, often employed in field research, whereby each person interviewed may be asked to suggest additional people for interviewing

### quota sampling

a type of nonprobability sampling in which units are selected into a sample on the basis of prespecified characteristicsm so that the total sample will have the same distribution of characteristics assumed to exist in the population being studied.

### informant

someone well versed in the social phenomenon that you wish to study and who is willing to tell you what he or she knows about it.

### probability sampling

the general term for samples selected in accord with probability theory, typically involving some random-selecting mechanism. (specific types include EPSEM, PPS, simple random sampling and systematic sampling

### representativeness

that quatlity of a sample of having the same distribution of characteristics as the population from which it was selected. Enchanced by probability sampling and provides for generalizability and the use of inferentail statistics.

### EPSEM (equal probability of selection method)

a sample design in which each member of the population has the same chance of being selected into the sample.

### 95% confidence interval

1.96 standard errors

### 99% confidence interval

2.58 standard errors

### 99.9% confidence interval

3.3 standard errors

### Law of Larege Numbers

as the size of the sample increase and becomes closer to the size of the total population, the mean and the vaiance will become closer to that found in the total population

### Central Limit Theorem

if repeated random sample of size N are selected from a normally distributed population, the the means of the samples will be normally distributed

### Column Variable has what variable in it?

Independent Variable

### Row Variable has what variable in it?

Dependent Variable

### Purpose of Chi Square

to estimate the probability of getting the distribution of values in a contingency table through sampling error, i.e. random chance;;; We want to accept a hypothesis that has little chance of occuring through sampling error