Statistical Sampling Part II – Language and Technique

This video is designed to accompany pages in Making Sense of Uncertainty Activities for Teaching Statistical Reasoning Van-Griner Publishing Company

Basic Language List of Individuals Population - 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

Critical Distinction Population Sample Statistic – 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-S

Identification of Terms Americans and Their Guns Title:Poll: Majority of Americans Back Stricter Gun Laws Authors:Sarah Dutton, Jennifer De Pinto, Anthony Salvanto, Fred Backus, Leigh Ann Caldwell Source: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 N 2. Use

Subtle and Critical Keys to confidence in your parameter estimate? 1. The probabilistic nature of the sample selection 2.Some really neat mathematics

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.