Definitions
The entire group of individuals we want information about in a statistical study.
Population
Is this questions a valid or invalid statistical question: How much money do high school students carry with them?
Valid
A method of sampling that involves using a chance process to determine which members of a population are included in the sample.
random sampling
A sample of size n chosen in such a way that every group of n individuals in the population has an equal chance of being selected as the sample.
simple random sample (SRS)
Occurs when some members of the population are less likely to be chosen or cannot be chosen for the sample.
undercoverage
A method of collecting data from every individual in the population.
Census
Is this questions a valid or invalid statistical question: How many quarters in $10?
Not Valid
The design of a statistical study shows _______ if it consistently underestimates or consistently overestimates the value you want to know when the study is repeated many times.
bias
The fact that different random samples of the same size from the same population produce different estimates.
sampling variability
Occurs when an individual chosen for the sample can't be contacted or refuses to participate.
nonresponse
A subset of individuals in the population from which we collect data.
Sample
Identify the population: A wildlife biologist in Alaska tranquilizes 42 grizzly bears, records their weights and then releases them.
All grizzly bears in Alaska
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
Describes how far, at most, we expect an estimate to vary from the true population value. That is, in a C% confidence interval, the distance between the point estimate and the true parameter value will be less than the margin of error in C% of all samples.
Margin of Error
Occurs when there is a consistent pattern of inaccurate responses to a survey question.
response bias
A study that observes individuals and measures variables of interest, but does not attempt to influence the responses.
Observational Study
Identify the sample: A teenager selects 15 Beyonce songs and counts the number of words in each song.
15 Beyonce songs
Convenience Sample or Voluntary Response Sample? After a controversial decision made by the mayor, 90% of the letters to the newspaper editor expressed opposition to the mayor's action.
Voluntary Reponse
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
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
A study that deliberately imposes some treatment on individuals to measure their responses.
Experimental Study
Determine if this is an Observational or Experiment study:
Sixty 4-year-old children. One group was shown a fast paced cartoon, one group was shown an educational cartoon and one group was given art supplies and told to draw pictures. At the end they were tested on their ability to make decisions.
Experiment
Sammy wants to know what percent of students at her high school have a driver's license. She surveys all student in her stats class and fins that 68% of the students in her sample have driver's license. What type of sample did Sammy obtain?
Convenience Sample
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
Undercoverage, Nonresponse or Response Bias?
A survey at a recent alumni reunion for a large university asked about their annual income of the 2431 alums. Of the 42 alums who responded, the mean income was $132,473.
Nonresponse Bias
The fact that different random samples of the same size from the same population produce different estimates.
sampling variability
Observational
To fund a problem to buy electronic tablets for every 2nd grade student in Springdale public schools, the board of education proposes a 5% increase in property taxes. One local "golden oldies" radio station asks listeners to voice opinion. 78% of the callers were opposed. What type of sample did the radio station obtain?
Voluntary Response
How can we decrease the margin of error?
Increase the sample size.
Undercoverage, Nonresponse or Response Bias?
A veterinarian examines the records of a random sample of 100 dogs enrolled in her practice and find that 2% of these dogs are malnourished.
Undercoverage