Planning a study
All the members of a uniquely definable group of people or things.
Population
A sampling method in which the researcher randomly selects a subset of participants from a population
Simple Random Sample (SRS)
Whoever wants to respond to the survey does - focus on people who responded and what they want
Voluntary bias
Occurs when some members of the population are less likely to be chosen or cannot be chosen for the sample.
Undercoverage
Convenience Sample or Voluntary Response Sample?
A mall interviewer approaches people passing by in the shopping mall asking about the current unemployment rate in the city where the mall is located.
Convenience Sample
Sample
Combines more than one sampling method.
Multistage
Only 10% responded - focus on the number of people who did not respond (Number of answers you got vs number of surveys you gave)
Nonresponse bias
Occurs when an individual chosen for the sample can't be contacted or refuses to participate.
Nonresponse
Identify the population: A wildlife biologist in Alaska tranquilizes 42 grizzly bears, records their weights and then releases them.
All grizzly bears in Alaska
A method of collecting data from every individual in the population.
Census
A sampling method in which you first divide the population into smaller groups, or strata, based on shared characteristics and then randomly sample.
Stratified Random Sample
Some proportion of the population is not sampled
Undercoverage
How can we decrease the margin of error?
Increase sample size
Identify the sample: A teenager selects 15 Beyonce songs and counts the number of words in each song.
15 Beyonce songs
A study that observes individuals and measures variables of interest, but does not attempt to influence the responses.
Observational Study
A sampling method in which randomly select first individual then use a method for picking each subsequent individual
Systematic
Something in the survey design that influences the response (present personal bias before presenting question/wording of question/leading question- response)
Response bias
A research study that follows over time groups of individuals who are alike in many ways but differ by a certain characteristic
Prospective study/experiment
Undercoverage, Nonresponse or Response Bias?
A police officer surveys a random sample of 100 attendees at a police officers' convention and finds that 7% admitted to breaking the speed limit more than 3 times last week on their drive to work.
Response bias
The fact that different random samples of the same size from the same population produce different estimates.
Sampling Variability
A sampling method in which the entire population of the study is divided into externally, homogeneous but internally, heterogeneous groups- then groups are picked from those divisions, and all individuals/items within the group are tested.
Cluster Census
Collecting data via intent, call, at a shopping mall
Convenience sampling
One question in the Census at School survey is "How long does it usually take you to get to school?" In a random sample of responses from 20 U.S. students from grades 9-12 had a mean of 15.95 minutes and a standard deviation of 2.117. Approximate the margin of error for the estimate of the mean time to travel to school.
Margin of error = 2(2.117) = 4.234 minutes
A Harris Poll surveyed a random sample of 2232 U.S. adults. The mean of .33 (33%) with a standard deviation of 0.011 of the people somewhat or strongly agreed that they expect to receive gifts on Valentine's Day. What is the approximate of the margin of error?
Margin of Error = 2(0.011) = 0.022