Chapter 5: Sampling

representative sample

a sample that looks like the population from which it was selected in all respects that are potentially relevant to the study. The distribution of characteristics among the elements of it is the same as the distribution of those characteristics among the total population.

periodicity

a sequence of elements (in a list to be sampled) that varies in some regular, periodic pattern

target population

a set of elements larger than or different from the population sampled and to which the researcher would like to generalize study findings

population parameter

a statistic computed for the entire population

sample

a subset of elements from the larger population

normal distribution

a symmetric distribution shaped like a bell and centered around the population mean, with the number of cases tapering off in a predictable pattern on both sides of the mean

random number table

a table containing lists of numbers that are ordered solely on the basis of chance; it is used for drawing a random sample

sampling error

any difference between the characteristics of a sample and the characteristics of the population from which it was drawn. The larger the sampling error, the less representative the same is of the population

random sampling error

differences between the population and the sample that are due only to chance factors (random error), not to systematic sampling error. It may or may not result in an unrepresentative sample. The magnitude of it due to chance factors can be estimated statistically.

sample generalizability

exists when a conclusion based on a sample, subset, or a larger population holds true for that population

cross-population generalizability (external validity)

exists when findings about one group, population, or setting hold true for other groups, populations, or settings

inferential statistics

mathematical tools for estimating how likely it is that a statistical result based on data from a random sample is representative of the population from which the population was selected

systematic sampling error

overrepresentation or underrepresentation of some population characteristics in a sample due to the method used to select the sample. A sample affected by systematic sampling error is a biased sample.

nonresponse

people or other entities who do not participate in a study although they are selected for the sample

census

research in which info is obtained through the responses that all available members of an entire population give to questions

disproportionate stratified sampling

sampling in which elements are selected from strata in different proportions from those that appear in the population

multistage cluster sampling

sampling in which elements are selected in two or more stages, with the first stage being the random selection of naturally occurring clusters and the last stage being the random selection of multilevel elements within clusters

availability sampling

sampling in which elements are selected on the basis of convenience

proportionate stratified sampling

sampling methods in which elements are selected from strata in exact proportion to their representation in the population

nonprobability sampling methods

sampling methods in which the probability of selection of population elements is unknown

probability sampling methods

sampling methods that rely on a random, or chance, selection method to that the probability of a selection of population elements is known

units of observation

the cases about which measure actually are obtained in a sample

population

the entire set of elements in which we are interested

random selection

the fundamental element of probability samples; the essential characteristic of random selection is that every element of the population has a known and independent chance of being selected into the sample

units analysis

the level of social life on which a research question is focused, such as individuals

probability of selection

the likelihood that an element will be selected from the population for inclusion in the sample. When the size of the desired sample as a proportion of the population decreases, so does the probability of selection ex: In a census of all the elements of a population, the probability that any particular element will be selected is 1 because anyone will be selected.

sampling interval

the number of cases from one sampled case to another in a systematic random sample

random digit dialing (RDD)

the random dialing by a machine of numbers within designated phone prefixes, which creates a random sample for phone surveys

confidence interval

the range defined by the confidence limits for a sample statistic

sampling units

the units actually selected in each stage of sampling

confidence limits

the upper and lower bounds around an estimate of a population parameter based on a sample statistic. They show how much confidence can be placed in the estimate

enumeration units

units that contain one or more elements and that are listed in a sampling frame

sample statistic

an estimated statistic from the one one sample we actually selected from a population

sampling distribution

a distribution of the value of a statistic from many samples

sampling frame

a list of the elements of a population from which a sample actually is selected

simple random sampling

a method of random sampling in which every sample element is selected only on the basis of chance, through a random process

replacement sampling

a method of sampling in which sample elements are returned to the sampling frame after being selected, so they may be sampled again. Random samples may be selected with or without replacement

snowball sampling

a method of sampling in which sample elements are selected as they are identified by successive informants or interviewees

systematic random sampling

a method of sampling in which sample elements are selected from a list or from sequential files, which every nth element being selected after the first element is selected randomly within the first interval

stratified random sampling

a method of sampling in which sample elements are selected separately from population strata that are identified in advance by the researcher

cluster

a naturally occurring, mixed aggregate of elements in the population

purposive sampling

a nonprobability sampling method in which elements are selected for a purpose, usually because of their unique position. Sometimes referred to as judgment sampling

quota sampling

a nonprobability sampling method in which elements are selected to ensure that the sample represents certain characteristics in proportion to their prevalence in the population

ecological fallacy

an error in reasoning in which incorrect conclusions about individual level processes are drawn from group-level data

reductionist fallacy (reductionism)

an error in reasoning that occurs when incorrect conclusions about group-level processes are based on individual-level data