Estimating Dates: Scatterplots

Transcription

1 activity 2.1 Estimating Dates: Scatterplots In this activity, you will estimate the dates of several major events and then use a scatterplot to compare your estimates with the actual dates these events occurred. You will analyze relationships between two variables that can be read from a scatterplot. You will start with an estimation experiment. Work with one or two classmates and fill in the following table, giving your group s best estimate of the year in which each event occurred. 1. For each of the following twentieth century events, estimate the year in which the event occurred. (Record only the last two digits of the year; because you know all dates are in the 1900s, you don t need to record the 19. ) Event Estimated Year Event Occurred Oprah Winfrey born Martin Luther King assassinated Original Woodstock music festival held

2 406 Excel Activities Event Estimated Year Event Occurred Nineteenth amendment established women s suffrage Long-distance telegraphic radio signal sent across the Atlantic Bart Simpson s character made his debut Aerosol can invented Franklin D. Roosevelt elected to a third term of office Scotch tape invented Hank Aaron inducted into the Baseball Hall of Fame Pearl Harbor bombed President Nixon resigned Schindler s List won the Academy Award for best picture San Francisco destroyed by earthquake and fire The World Wide Web developed 2. Obtain the actual dates for those events from your instructor. Create a scatterplot of the data with x representing year event occurred and y representing estimated year event occurred. (You might want to record these actual dates immediately to the left of your estimates in the previous table.)

3 Activity 2.1: Estimating Dates Why is it appropriate to use the variable year event occurred as the explanatory variable and estimated year event occurred as the response variable? 4. How close were your predictions of events that occurred in the 1980s to the actual dates?

4 408 Excel Activities 5. What would the scatterplot look like if you had guessed the correct year for each event? 6. Sketch the line y = x on your graph. Does it appear that you overestimated more than you underestimated or that you underestimated more than you overestimated or neither? How did you determine this from your graph? 7. Use Excel to redraw the scatterplot you created previously. To do so, you need to enter the data in two columns. One column should contain the values of the explanatory variable and the second column the values of the response variable. Instructions to Use Excel to Create a Scatterplot a. b. Get the file EA2.1 Events and Dates.xls from the CD or website. In column C of the Excel worksheet, enter your estimates of the year each of the events occurred (enter only the last two digits of the year). Add an appropriate column title in cell C1. To create a scatterplot of the x-y data with x representing year event occurred and y representing estimated year event occurred, select the two columns of data, including the labels. Go to the Insert tab and choose Scatter from the Charts group and click on the first type of graph (the dots ).

5 Activity 2.1: Estimating Dates 409 c. d. Select the graph by clicking inside the border of the graph. Go to Chart Layouts and select Layout 1 (the first one in the first row.) Enter a relevant chart title and titles for the two axes. Also, click on the legend and delete it by pressing the Delete key. Note that you can find the coordinates of any point on your completed graph by moving the cursor to the point. If you want to change the scale on either axis, point to the numbers on the axis and right-click; then select Format Axis. Then, using the Axis Options, select Fixed for Minimum and Maximum and enter the appropriate minimum and maximum values for your axis. Finally, click Close. 8. Change your estimated values so the values of estimated year event occurred and the values of year event occurred are equal and look at the corresponding scatterplot. Describe the graph. Does your description agree with your answer in #5? Additional Questions 1. The following data gives the number of strikes or lockouts involving more than 1,000 workers, and the percentage of the total labor force belonging to a union between the years 1950 and (Source: Encyclopedia Britannica Almanac 2004, pages ) Year Strikes and Lockouts Union Membership Percentage

6 410 Excel Activities Year Strikes and Lockouts Union Membership Percentage a. What kinds of information, related to these data, would you want to get from a graph? b. Create a scatterplot that relates the number of strikes and lockouts with the percentage of the total labor force with union membership.

7 Activity 2.1: Estimating Dates 411 c. Which variable did you use as the explanatory variable? Why? d. Explain what your graph shows. 2. Create two other scatterplots using data from the previous table. Explain what each graph shows. Summary In this activity, you learned how to use Excel to create a scatterplot. In creating scatterplots, you decided which variable should go on the horizontal axis (that is, which variable is the explanatory variable) and which should go on the vertical axis (that is, which is the response variable). You also discovered how the line y = x can help you see relationships in paired data. You will use these skills to visualize relationships between variables in bivariate data sets.