• the best-fit-line on a scatter diagram is a line that lies closer to the data points than any other possible line ( according to a standard statistical measure of closeness) 
• predictions with best-fit lines 
• don't expect a best-fit line to give a good prediction 
• a best fit line based on past data is not necessarily calid now and might not result in valid predictions of the future 
• dont make predictions about a population that is different from the population from which the sample data were drawn 
• valid predictions? 
• youve found a best-fit line for a correlation between the number of hours per day that people excercise and the number of calories they consume each day. You used this correlation to predict that a person who excercises 18 hours per day 
• no one excercises 18 hours a day 
• bes fit lines nd r^2 -  the square of the correlation coefficent, or r^2, is the proportion of the variation in a variable that is accounted for by the best-fit line 
• the coefficent of derermination represents 
• the coefficent determination represents the percent of the data that is the closest to the line 
• political scientists are interested in knowing what factors affect voter turnout in elections/ One such factor is the unemployment . 
• the square of the correlation coefficients is r^2