Flashcards in 2.1 and 2.2 Deck (19):
A study in which the investigator observes characteristics of a sample selected from one or more existing populations.
What is the goal of an observational study?
Draw conclusions about the corresponding population or about differences between two or more populations.
A study in which the investigator observes how a response variable behaves when one or more explanatory variables are manipulated
What is the goal on an experiment?
To determine the effect of the manipulated explanatory variables on the response variable.
A variable that is related to both how the experimental groups were formed and the response variable of interest.
Tendency for samples to differ from the corresponding population as a result of systematic exclusion of some part of the population
Measurement or Response Bias
Tendency for samples to differ from the corresponding population because the method of observation tend to produce values that differ from the true value.
Tendency for samples to differ from the corresponding population because data are not obtained from all individuals selected for inclusion in the sample
Simple Random Sample
A sample that is selected from a population in a way that ensures that every different possible sample of size n has the same chance of being selected
Sampling without Replacement
Once an individual from the population is selected for inclusion in the sample, it may not be selected again in the sampling process
Sampling with Replacement
After an individual from the population is selected for inclusion in the sample and the corresponding data are recorded, the individual is placed back in the population and can be selected again in the sampling process
Dividing a population into subgroups and then taking a separate random sample from each stratum.
Dividing a population into subgroups and forming a sample by randomly selecting clusters and including all individuals or objects in the selected clusters in the sample.
A value k is specified (for example k = 50 or k = 200).
One of the first k individuals is selected at random.
Then every kth individual in the sequence is included in the sample.
The Educational Testing Service (ETS) needed a sample of colleges. ETS first divided all colleges into groups of similar types (small public, small private, medium public, medium private, large public, and large private). Then they randomly selected 3 colleges from each group.
A county commissioner wants to survey people in her district to determine their opinions on a particular law up for adoption. She decides to randomly select blocks in her district and then survey all who live on those blocks.
A local restaurant manager wants to survey customers about the service they receive. Each night the manager randomly chooses a number between 1 & 10. He then gives a survey to that customer, and to every 10th customer after them, to fill it out before they leave.
Using an easily available or convenient group to form a sample.