Day 4: Where Do Data Come From (Cont) Census and Experiment Unit 1: Collecting Data Day 4: Where Do Data Come From (Cont) Census and Experiment

Warm-up: TV Ratings Market research is designed to discover what consumers want and what products they use. One example of market research is the television-rating service of Nielsen Media Research. They ask about 5000 households to use a “people meter” to record the TV viewing of all people in the household. The Nielsen ratings influence how much advertisers will pay to sponsor a program and whether or not the program stays on the air. At the time of this study, 100 million U.S. households had a television set. What are the population and sample? What are possible variables? Population: The 100 million U.S. households that have a television set Sample: About 5000 households using the “people meter” Variables: Number of people in the household and their age/sex Whether the TV set is in use at each time period What programs are watched Who is watching etc

Census What is a census? Census: a sample survey that attempts to include the entire population in the sample Examples? Why not always do a census? Examples: US census, asking all students at a school, asking all employees at a company Why not? Expensive, time consuming, when testing products (example: fireworks) you can’t destroy all of them, whole population isn’t available

US Census interesting facts Conducted every 10 years since 1790 but replacements are in the works A census “long form” that asks more questions than the basic census form is sent to a sample of one-sixth of all households (eliminated after 2000) 1990 census missed and estimated1.8% of the US population (primarily African- Americans in inner cities) In 2000, the census over counted the US population by 1.3 million. How could that happen?? Main purpose is to create election districts with equal population. Application: Making Sense of the Census How? People that live in two places (like college students) were counted twice