Chapter 1 Section 1

Data What is Statistics? The science of collecting, organizing, and interpreting numerical facts, which we call data Data (def.) – the numbers or information collected in a study or experiment.

How is collect data We should ask the following questions first! Who What Where When Why How do we determine if the information is a valid representation of their claim?

Measurements Measurements are made on individuals and organized in variables. Individuals are objects described by data, can be people, animals or things. Variables are the characteristics of an individual. A variable can take different values for different individuals.

Example 1 Consider 17, 21, 44, and 76. Are those data? Context is critical...they could be test scores, ages in a golf foursome, or uniform numbers of the starting backfield on the football team. In each case our reaction changes.

Annual Death by Drugs

They are all rounded

Example Political party preference in the United Sates depends in part on age, income, and the gender of the voter. A political scientist selects a large sample of registered voters. For each voter, she records gender, age, household income, and whether they voted for the Democratic or Republican candidate in the last congressional election. What are the individuals in this situation? And, what are the variables? Individuals: Voters Variables: gender, age, household income, and whether they voted for the Democratic or Republican candidate in the last congressional election

Types of Variables Categorical Variable places the individual into one of the several groups or categories Quantitative Variable has a numerical value.

Example Political party preference in the United Sates depends in part on age, income, and the gender of the voter. A political scientist selects a large sample of registered voters. For each voter, she records gender, age, household income, and whether they voted for the Democratic or Republican candidate in the last congressional election. Which variable are categorical, and which are quantitative? Categorical: Gender, political alliance Quantitative: Age, Income (gender?)

Big Idea The distinction between treating data as categorical or quantitative may be more about how we display and analyze data than it is about the variable itself. For Example: “sex” is data, but just because we label a male as a 1 and a female as a 0, doesn’t make it quantitative. However, we could then average the 0’s and 1’s to give us a percentage of males vs females.

Thought Could you make make age categorical? Break them into categories (child, adult, and senior) Therefore context is important and the W’s in summarizing these data help to make sure we describe our data correctly.

Example Identify the W’s (who, what where when, where and how. As well as whether they are categorical or quantitative. A report on the Boston marathon listed each runner’s gender, country, age and time.

ANSWERS Who: Boston Marathon Runners What: gender, country, time, age When: Not specified Where: Boston How: Not specified, but assumed through registration form Why: race result reporting Categorical: Gender, Country Quantitative: Age (years), Time (hours, minutes, seconds)

1.1 homework 1

Yesterday We talked about how we look at and analyze other people’s already collected data but let’s talk about how it gets collected to begin with!

How do we gather data? One way to gather data is to OBSERVE. The important thing to remember about observing is that you do nothing. You watch, ask. You do not influence the response. An observational study observes individuals and measures variables of interest but does not attempt to influence the responses. The purpose of an observational study is to describe some group or situations.

Experiment Another way to gather data is to conduct an EXPERIMENT. An experiment deliberately imposes some treatment on individuals in order to observe their responses.

Other methods Sampling is gaining information about the whole by examining only a part. Observational studies that use sampling are called sample surveys. Population is the entire group of individuals about which we want information. Sample is a part of the population from which we actually collect information, which is then used to draw conclusions about the whole.

Census A census is a sample survey that attempts to include the entire population in the sample. Frog Fairy Tale Correct Answer - 83

Study purpose is often to investigate the relationship between two variables Do taller people make more money? Do magnets help relieve pain?

Variables • Explanatory variable is the one that may cause or explain the differences in the response variable Do taller people make more money? Explanatory variable ___________ Response variable____________ Do magnets help relieve pain? Response variable_____________

Observation Study vs. Experiment IMPORTANT: An observational study may reveal correlation between two variables, but only a randomized experiment can prove cause‐and‐effect Why??? Random assignment to treatment and control groups in an experiment helps equalize the groups with respect to any confounding variables so any difference in the response is attributable to the explanatory variable

Example: Pets and Happiness A study is conducted to investigate the relationship between owning pets and happiness. 100 subjects are randomly selected and data on whether or not a pet is owned and a happiness score (1‐10, 10 being extremely happy) are obtained. Explanatory and response variables? Observational or Experiment?

Example: Video Games and Aggression 210 college students were randomly assigned to played either a violent (Wolfenstein 3D) or nonviolent video game (Myst) A short time later, the students who played the violent video game punished an opponent (received a noise blast with varying intensity) for a longer period of time than did students who had played the nonviolent video game. Article: "Video Games and Aggressive Thoughts, Feelings, and Behavior in the Laboratory and in Life," Craig A. Anderson, Ph.D., Iowa State University of Science and Technology and Karen E. Dill, Ph.D., Lenoir‐ Rhyne College, Journal of Personality and Social Psychology, Vol. 78, No. 4.

Example: Video Games and Aggression Observational or randomized experiment? Explanatory variable? Response variable? Can cause and effect be established?

Homework