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4  Scatterplots What is a scatter plot? BEFORE you add any lines or curves to the scatter plot make a visual interpretation...in context Is the association linear looking or not? If there looks like a linear association then you con preceded with applying a linear model. What can we describe from a of scatter plot? If the scatterplot indicates a linear model is appropriate then we can proceed. Discuss what you see in your scatterplots "i would expect that measurements of (blah) and (blah) are in proportion" Investigate the effect of other variables or groups 
Class notes, Class notes AIS p99 Booklet pg2 (describe scatter plot & variable types, and research question. (Java app) Build your own scatter plot You can add points to the plot and move points around. See the effects on the least squares fitted line (the plotted line and its equation) and the correlation coefficient. (link to www.ruf.rice.edu) Class Exemplar: Class Exemplar: 
What do I look for in scatterplots? 

Trend 
Do you see: a linear trend… 
or a nonlinear trend? 
Association 
Do you see: a positive association as one variable gets bigger, so does the other 
as one variable gets bigger, the other gets smaller 
Strength 
little scatter (Strong) 
lots of scatter (Weak) 
Groups 
Do you see any groupings? 

Unusual Values 
Do you see any Unusual values? 

Scatter 
Do you see: constant scatter… roughly the same amount of scatter as you look across the plot

or nonconstant scatter? the scatter looks like a “fan” or “funnel” 


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Average Age New Zealanders are First Married 



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