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Statistics: Unlocking the Power of Data Lock 5 Chapter 1 Collecting Data
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Statistics: Unlocking the Power of Data Lock 5 Section 1.3 Experiments and Observational Studies
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Statistics: Unlocking the Power of Data Lock 5 Outline Association versus Causation Confounding Variables Observational Studies vs Experiments Randomized Experiments
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Statistics: Unlocking the Power of Data Lock 5 Learning Goals Recognize that not every association implies causation Identify potential confounding variables in a study Distinguish between an observational study and randomized experiment Distinguish between randomized comparative experiment and matched pairs experiment
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Statistics: Unlocking the Power of Data Lock 5 Association and Causation Two variables are associated if values of one variable tend to be related to values of the other variable Two variables are causally associated if changing the value of the explanatory variable influences the value of the response variable
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Statistics: Unlocking the Power of Data Lock 5 Explanatory, Response, Causation For each of the following headlines: Identify the explanatory and response variables (if appropriate). Does the headline imply a causal association? 1. “Daily Exercise Improves Mental Performance 2. “Want to lose weight ? Eat more fiber !
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Statistics: Unlocking the Power of Data Lock 5 Roles of Variables Response Variable The variable of interest. It is what we want to predict. It is an main outcome of study Explanatory or Predictor Variable: The variable that we use to provide information or a prediction of the response variable Choosing the response variable and the explanatory variable depends on how we think about the problem
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Statistics: Unlocking the Power of Data Lock 5 Identifying Response and Explanatory Variable? Do students with higher SAT scores get better grades? Grades = Response SAT score = Explanatory Can we estimate a person’s BMI by measuring their wrist size? BMI = Response Wrist Size = Explanatory Response variable: Measures an outcome of study Explanatory variable: explains or influences a response variable
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Statistics: Unlocking the Power of Data Lock 5 Association and Causation ASSOCIATION IS NOT NECESSARILY CAUSAL! Come up with two variables that are associated , but not causally Come up with two variables that are causally associated Which is the explanatory variable? Which is the response variable?
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Statistics: Unlocking the Power of Data Lock 5 0 200 400 600 800 1000 40 50 60 70 80 TVs per 1000 People Life Expectancy Angola Australia Cambodia Canada China Egypt France Haiti Iraq Japan Madagascar Mexico Morocco Pakistan Russia South Africa Sri Lanka Uganda United Kingdom United States Vietnam Yemen r = 0.74 TVs and Life Expectancy Should you buy more TVs to live longer?
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