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Phil12_S11_Predicting_relationships_between variables(4-28-2011)

# Phil12_S11_Predicting_relationships_between variables(4-28-2011)

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Predicting relationships between variables Phil 12: Logic and Decision Making Spring 2011 UC San Diego 4/28/2011 Thursday, April 28, 2011

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Where we’ve been Variables: things that vary Variables differ in the way they can be measured - nominal & ordinal vs. score variables Hypotheses: conjectures about the way some phenomenon behaves - Need to be tested by predictions One type of hypothesis: how a single variable is distributed - Ages of people in food court - Amount of time animal spends foraging - Amount of time you spend studying Thursday, April 28, 2011
Hypotheses involving more than one variable Amount of sleep and ability to recall information Pressure, volume, and temperature of a gas Experience and job performance SAT score and grades in college Vitamin intake and health condition Sexual activity and sexually transmitted diseases Smoking and lung cancer Miles per gallon and horsepower of cars Thursday, April 28, 2011

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Clicker question More than 98% of convicted felons are bread eaters. Does this mean bread-eating is related to criminal activity? A. Yes B. No Thursday, April 28, 2011
The case against bread More than 98% of convicted felons are bread eaters. Fully half of all children who grow up in bread consuming households score below average on standardized tests. In the 18th century, when virtually all bread was baked in the home, the average life expectancy was less than 50 years. More than 90% of all violent crimes are committed within 24 hours of eating bread. Primitive tribal societies that have no bread exhibit a low incidence of cancer, Alzheimer's, and Parkinson's disease. Not all statistics meaningful! Thursday, April 28, 2011

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Correlational and causal hypotheses Many of the hypotheses of interest in science and in ordinary life are causal: - Red wine and (reduced) cholesterol levels - Smoking and lung cancer - Vitamin C and prevention of colds - Deficit spending and economic recovery - Use of imagery and increased memory But causal claims are more difficult to establish than correlational claims So for now we focus on correlations only Thursday, April 28, 2011
Correlations and why they are interesting A correlational claim says that the values on two variables vary systematically - Not necessarily in the same direction Why care about correlations if they are not (known to be) causal? 1. They may indicate causal relations 2. They can be used to make predictions about the value of one variable from the known value of another variable Thursday, April 28, 2011

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SAT and College Grades Should the SAT be used as a (or maybe the) basis for admission to the University of California?
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