GATHERING AND PRODUCING DATA. How Data are Obtained. Census Everyone is included Observational Study Observes individuals and measures variables but does not attempt to influence responses Includes surveys and polls Experiment
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Minneapolis Star Tribune: “A Gallup Poll, conducted Aug. 16-18, 1999, asked, ‘Do you consider pro-wrestling to be a sport, or not?’ Of the people polled, 19% said, “Yes.” (Results were based on telephone interviews with a randomly selected national sample of 1,028 adults, 18 years and older.)”
p = ?
A carload of ball bearings has an average diameter of 2.502 centimeters. This is within the specifications for acceptance of the lot by the purchaser. An inspector happens to inspect 100 bearings from the lot and finds the average diameter of these to be 2.499 cm. This is within the specified limits, so the entire lot is accepted.
µ = 2.502 cm (The population mean.)
= 2.499 cm (The sample mean.)
on average the sample looks like
the rest of the population.
estimate a population parameter,
sampling variability is sometimes
called “sampling error.”
height of all students will have a large sampling error, but it is not biased.
240 x .20 = 48 Arts and Lit students
240 x .15 = 36 Humanities students
240 x .30 = 72 Social science students
240 x .35 = 84 Natural science students
Hospital administrators are concerned about the possibility of drug abuse among employees. They plan to pick a sample of 40 from 800 employees, and administer a drug test. What’s the sampling strategy?
mixed enough a tablespoon will
suffice, whether you’re “sampling”
from a saucepan or from a barrel.
. But you’ll have to wait until we get to Statistical Inference to learn why.
“If you had it to do over again, would you have children?”