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BiVariate Data When two pieces of data are collected Data can be organized as a SCATTERPLOT – if data is numbers Or in a TWO WAY TABLE – if data is categories edited version of ccollins @ www.lemars.k12.ia.us

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Scatter Plot A scatter plot is a graph of a collection of ordered pairs (x,y). The graph looks like a group of dots, but some of the graphs move in a general direction.

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Positive Association If the x-coordinates and the y-coordinates both increase, then it is POSITIVE ASSOCIATION This means that both values are going up and a line of best fit can be drawn Line of best fit shows the general direction that a group of points seems to be heading

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Positive Association If you look at the age of a child and the child’s height, you will find that as the child gets older, the child gets taller. Because both are going up, it is positive correlation.

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Negative Association This means the two are related as opposites and a line of best fit can be drawn. If the y-coordinates decrease while the x-coordinates increase then it is NEGATIVE ASSOCIATION.

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Negative Association If you look at the age of your family’s car and its value, you will find as the car gets older, the car is worth less. This is negative association.

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No Association If there seems to be no pattern, and the points looked scattered, then it is no association. This means the two are not related.

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No Association If you look at the size shoe a baseball player wears, and their batting average, you will find that the shoe size does not make the player better or worse, then are not related.

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Scatterplots Which scatterplots below show a linear trend? a) c)e) b) d)f) Negative Association Positive Association Constant Association

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Scatterplots cluster outlier non-linear linear cluster – points are near each other – not necessarily any other correlation outlier – when a point is not near the line of best fit non-linear association the pattern of the points is predictable, but not a line linear association a line of best fit can be drawn and predictions can be made

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Year Sport Utility Vehicles (SUVs) Sales in U.S. Sales (in Millions) 1991 1992 1993 1994 1995 1996 1997 1998 1999 0.9 1.1 1.4 1.6 1.7 2.1 2.4 2.7 3.2 1991 1993 1995 1997 1999 1992 1994 1996 1998 2000 x y Year Vehicle Sales (Millions) 5432154321 Objective - To plot data points in the coordinate plane and interpret scatter plots.

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1991 1993 1995 1997 1999 1992 1994 1996 1998 2000 x y Year Vehicle Sales (Millions) 5432154321 Trend is increasing. Scatterplot - a coordinate graph of data points. Trend appears linear. Positive association. Predict the sales in 2001.

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If bivariate data is about categories -not numbers- it is displayed in a Two Way Frequency Table similar information to a venn diagram Although all the information is not given, using reason we can complete the table 21 22 7030100

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A Relative Frequency Table Shows the percent in each category – Frequency can be compared to rows or columns 21 22 7030100 The relative frequency of cell phone owners who own a mp3 player is… cell phone TOTAL mp3 57 70 =.81 you have to read carefully!!! you are comparing to mp3

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21 22 7030100 mp3no mp3total cell phone/70/30/100 no cell/70/30/100 total what is the relative frequency

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mp3no mp3total cell phone57/7021/3078/100 no cell13/709/3022/100 total70/7030/30100/100 mp3no mp3total cell phone.81.70.78 no cell.19.30.22 total1.00

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