Chapter-3-09-10

Chapter-3-09-10 - Chapter 3: Examining Relationships Intro:...

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Chapter 3: Examining Relationships
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Intro: This section is going to focus on relationships among several variables for the same group of individuals. In these relationships, does one variable cause the other variable to change? In this relationship we can think of one variable as the explanatory variable and the other as the response variable. A response variable measures an outcome of a study. An explanatory variable attempts to explain the observed outcomes. Other names for the two variables are independent variables and dependent variables. 2
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Principles that guide examination of data are the same for studying relationships among variables as they were for one- variable methods from chapters 1 and 2. First plot the data, then add numerical summaries. Look for overall patterns and deviation from those patterns. When the overall pattern is quite regular, use a compact mathematical model to describe it. 3
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Section 3.1: Scatterplots The most effective way to display the relationship between two quantitative variables is a scatterplot. A scatterplot shows the relationship between two quantitative variables measured on the same individuals. Each individual in the data appears as the point in the plot. Always plot the explanatory variable, if there is one, on the horizontal axis and the response variable on the vertical axis. 6
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Examining scatterplots: In any given graph of data, look for the overall pattern and for striking deviations from that pattern. You can describe the overall pattern of a scatterplot by the form, direction, and strength of the relationship. Form – linear, quadratic, logarithmic, ect. Direction – positive or negative. Strength – weak, moderate, or strong. 8
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An important kind of deviation is an outlier. Two variables are positively associated if an increase in one variable is tied together with an increase in the other. Two variables are negatively associated if an increase in one variable is tied together with a decrease in the other. 9
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This note was uploaded on 12/09/2011 for the course STATS 221 taught by Professor Nielson during the Fall '10 term at BYU.

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Chapter-3-09-10 - Chapter 3: Examining Relationships Intro:...

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