Observational Studies and Experiments

Observational Studies and Experiments

Statistics 50, Spring 2009

Introduction

? 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? Explanatory variable ___________ Response variable_____________

Variables

? Confounding variable

? Has an effect on the response variable ? Is related to the explanatory variable ? Can't separate the effect of the confounding and explanatory

variables

? Example: Does exercise prevent colds?

? For a sample of subjects, record the amount of exercise per week and the number of colds over a year. Suppose you find that more exercise is correlated with fewer colds.

? Explanatory variable ? Response variable ? List possible confounders:__________________________

Types of Research Studies

? Observational Study

? data are observed and collected on each subject ? NO manipulation of the subjects' environment

occurs

? Experiment

? Manipulate the subjects' environment, then ? Measure the response variable

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