Chap. 11 Flashcards
Population
an entire group of individuals you want information on
Sample
smaller group of individuals within the population
What is the major rule for a sample?
has to be representative
Sample surveys
designed to ask questions of a small group of people in the hope of learning something about the entire population
W’s of sampling
who: sample drawn
when and how: drawing the sample depends on what is practical
why: the population we are interested in
Biased sampling
under or overestimating some characteristics of the population
Common errors of biased sampling
relying on voluntary responses
under coverage of the population
nonresponse bias
response bias
Randomization
best defense against bias - each individual is given a fair, random chance of selection
Sample size
number of individuals in a sample
What does sample size determine?
how well the sample represents the population
Does the fraction of the population determine how well the population is represented?
no
Census
a sample that consists of the entire population
Population parameter
the numerical valued attribute of a model for a population
How to know the true value of a population parameter (mean income of all employed people in the country)
hope to estimate it through sampled data
Statistic / sample statistic
values calculated for sampled data
Which statistics are most favorable?
those that correspond to and thus estimate a population parameter
Representative
sample said to be representative if the statistics computed it accurately reflect the corresponding population parameters
Simple random sample (SRS)
sample in which each set of n elements in the population has an equal chance of selection
Sampling frame
list of individuals from whom the sample is drawn is called the sampling frame
What does it mean to be outside of the sampling frame?
individuals who may be inside the population of interest but aren’t in the sampling frame
Sampling variability
natural tendency of randomly drawn samples to differ from one another
Stratified random sample
population is divided into several subpopulations or strata. random individuals are drawn from each group so that the sample includes individuals from each, in a representative proportion. reduces variability
Cluster sample
entire groups or clusters are chosen at once. usually convenient, practical, or less costly.
Multistage sample
sampling schemes that combine several sampling methods
Systematic sample
drawn by selecting individuals systematically from a sampling frame. representative when there is no relationship between the order of the sampling frame (every 10th person)
Pilot survey
small trial run to a survey to check whether questions are clear. reduces errors to questions that are up to interpretation or ambiguous
Voluntary response bias
bias introduced to a sample when individuals can choose on their own weather to participate in the sample. invalid and cannot be recovered
Convenience sample
consists of individuals who are conveniently available. every individual in the population is not equally represented
Undercoverage
biases the sample in a way that gives part of the population less representation
Nonresponse bias
bias introduced when a large fraction of those who are sampled fail to respond.
What type of response is considered nonresponse?
voluntary response bias
Response bias
Anything in a survey design that influences responses falls under the heading of response bias. the wording of a question creates response bias, or who’s asking the question
