1. 2.4 Graphs That Enlighten and Graphs That Deceive
SWBAT construct a scatterplot
SWBAT define correlation coefficient
SWBAT construct a time-series graph
SWBAT construct a stemplot

2. Scatterplot (Scatter Diagram)
A plot of paired (x,y) quantitative data with a horizontal x-axis and a vertical y axis.
The horizontal axis is used for the first (x) variable
The vertical axis is used for the second (y) variable
The pattern of the plotted points is often helpful in determining whether there is a correlation (or relationship) between the two variables

3. Constructing a Scatterplot
Construct a horizontal axis for the values of the first variable
Construct a vertical axis for the values of the second variable
Plot the points
Label the axes

4. Example
The following data represents the numbers of cricket chirps per minute paired with temperatures in °F
Temperature (°F) 72 84 76 87 80 92 70 83
Chirps pre minute
960
1150
860
1200
900
1190
875
1040

5. Example Continued
Does there appear to be a relationship between chirps and temperature as is shown by the pattern of the points?

6. Correlation Coefficient
Linear correlation coefficient r: a value between -1 and 1
If r is close to 1: there is a strong positive correlation between variables
If r is close to -1: there is a strong negative correlation between variables
If r is close to 0 there does not appear to be a correlation

7. Time Series Graph
A graph of time-series data, which are quantitative data that have been collected at different points in time, such as monthly or yearly
It is often important to know when population values change over time

8. Example
A graph that shows the yearly high values of the Dow Jones Industrial Average for the New York Stock Exchange

9. Stemplot (Stem-and-leaf plot)
Represents quantitative data by separating each value into two parts: the stem (such as the leftmost digit) and the leaf (such as the rightmost digit)
Advantages
we can see the distribution of data while keeping the original data values
constructing a stemplot is a quick way to sort data (arrange them in order)

10. Constructing Stemplots
Leaves are arranged in increasing order, not the order in which they occur in the original list
If we turn the stemplot on its side, we can see a distribution of the data
Better stemplots are often obtained by first rounding the original data values
Stemplots can be expanded to create more rows and condensed to include fewer rows

11. Stemplots

12. Minutes Spent Watching TV Over the Last 18 Days
Example
Use the following data to create a stemplot
Minutes Spent Watching TV Over the Last 18 Days 48
125 98
147 45 94 92
101 75 90
120 61 60 63 65
136 84