What is a cluster sample? a probability sample that is used when no list of elements exists. The sampling frame initially consists of clusters of elements What is confidence (in a statistic)? the degree of belief that an estimated range of values - more specifically, a high or low value - includes or covers the population parameter What is a convenience sample? a nonprobability sample in which the selection of the elements is determined by the researcher's convenience What is a disproportionate sample? a stratified sample in which elements sharing a characteristic are underrepresented or overrepresented in the sample

 What is an element? a particular case or entity about which information is collected; the unit of analysis What is an estimator? a statistic based on sample observations that is used to estimate the numerical value of an unknown population parameter What is an expected value? the mean or average value of a sample statistic based on repeated samples from a population What is a nonprobability sample? a sample for which each element in the total population has an unknown probability of being selected

 What is non-response bias? Non-response bias occurs when some sampled subjects cannot be reached or refuse to participate or fail to answer some questions. What is a probability sample? a sample for which each element in the total population has a known probability of being selected What is a proportionate sample? a probability sample that draws elements from a stratified population at a rate proportional to the size of the samples What is a purposive sample? a nonprobability sample in which a researcher uses discretion in selecting elements for observation

 What is a quota sample? a nonprobability sample in which elements are sampled in proportion to their representation in the population What is random digit dialing? a procedure used to improve the representativeness of telephone samples by giving both listed and unlisted numbers a chance of selection What is a random start? selection of a number at random to determine where to start selecting elements in a systematic sample What is sample bias? the bias that occurs whenever some elements of a population are systematically excluded from a sample. It is usually due to an in complete sampling frame or a nonprobability method of selecting elements

 What is a sampling distribution? a theoretical (nonobserved) distribution of sample statistics calculated on samples of size N that, if known, permits the calculation of confidence intervals and the test of statistical hypothesis What is sampling error? the difference between a sample estimate and a corresponding population parameter that arises because only a portion of a population is observed What is a sampling fraction? the proportion of the population included in the sample What is a sampling interval? the number of elements in a sampling frame divided by the desired sample size

 What is a sampling unit? the entity listed in a sampling frame. It may be the same as an element, or it may be a group or cluster of elements What is a simple random sample? a sample in which each element has an equal chance of being selected What is a snowball sample? a sample in which respondents are asked to identify additional members of a population What is statistical inference? the mathematical theory and techniques for making conjectures about the unknown characteristics (parameters) of populations based on samples

 What is a stratified sample? a probability sample in which elements sharing one or more characteristics are grouped, and elements are selected from each group in proportion to the group's representation in the total population What is a stratum? a subgroup fo a population that shares one or more characteristics What is a systematic sample? a probability sample in which elements are selected from a list at predetermined intervals What is a weighting factor? a mathematical factor used to make a disproportionate sample representative