Statistical SamplingPart II – Language and Technique

This video is designed to accompany

pages 41-76

in

Making Sense of UncertaintyActivities for Teaching Statistical

ReasoningVan-Griner Publishing Company

Basic Language

List of Individuals123456789101112Population - Larger collection of

subjects/items that you are interested in understanding something about.

Sample - Subject/items that you are able to measure/interview. Chosen from population.

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Critical Distinction

Population

SampleStatistic – number that describes the sample. E.g. observed proportion in sample who answered “Yes”

Parameter – number that describes the population. E.g. true proportion of all U.K. students who would answer “Yes” to “Do you support gay marriage?”

Remember P-P

Remember S-S1 10 12

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Identification of Terms

Americans and Their Guns Title: Poll: Majority of Americans Back Stricter Gun LawsAuthors: Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus, Leigh Ann CaldwellSource: CBS News January 17, 2013

As the president outlined sweeping new proposals aimed to reduce gun violence, a new CBS News/New York Times poll found that Americans back the central components of the president's proposals, including background checks, a national gun sale database, limits on high capacity magazines and a ban on semi-automatic weapons. Asked if they generally back stricter gun laws, more than half of respondents - 54 percent - support stricter gun laws …. That is a jump from April - before the Newtown and Aurora shootings - when only 39 percent backed stricter gun laws but about the same as ten years ago.…This poll was conducted by telephone from January 11-15, 2013 among 1,110 adults nationwide. Phone numbers were dialed from samples of both standard land-line and cell phones. The error due to sampling for results based on the entire sample could be plus or minus three percentage points.

Statistic

Sample

Population (All

Americans)

Parameter - true, unknown percentage of ALL Americans who would have said they supported stricter gun laws, if all had been

asked.

A simple random sample (SRS) of size n consists of n individuals chosen from the population in such a way that every set of n individuals had the same chance of being chosen.

Simple Random Sampling

Practical Selection Tool

SRS of size n from N subjects? 1. Label objects 1 to N2. Use

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Subtle and Critical

Keys to confidence in your parameter estimate?

1. The probabilistic nature of the sample selection

2. Some really neat mathematics

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Common Confusion

A “fair” sample in a probabilistic sense is NOT a cross-sectional sample.

One of least understood, but most critical interpretations of what it means to sample “fairly.”

One-Sentence Reflection

A probabilistic sample like an SRS is a critical step in estimating a population parameter with a sample statistic.