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### Making and Interpreting Graphs

Guidelines for effective graph:

Twins

Peter and Paul are twin brothers. One of them (we don’t know which) always lies. The other one always tells the truth. I ask one of them:

“Is Paul the one that lies?”

“Yes,” he answers.

Did I speak to Peter or Paul?

Twins

I spoke to Peter

Average Speed

On the way to his grandmother’s house, John travels at an average of 30 mph. On the way back, he travels at an average of 40 mph. What was his average speed for the entire trip?

Average Speed

Suppose the distance is 120 miles.

That means 4hrs there, 3hrs back.

That’s 240 miles / 7 hrs = 34.3 mph

Review of Last Couple of Weeks

Linear or Exponential?

Roach population grows 5% every 2 days.

Every year, 15 more students attend Matt Forte High School.

There has been a $100 increase in wage every 6 months.

Review of Last Couple of Weeks

Linear or Exponential?

Review of Last Couple of Weeks

In how many years will a river expanding at 17.35% every year be three times its original size? Use Excel.

Week 3

What do we use graphs for?

- To better communicate information

Who uses graphs?

- Newspapers
- Magazines
- Work meetings

What types of graphs are there?

- Pie chart
- XY Graph
- Bar Chart

When do we use what?

- Pie Chart
- Limited applicability
- Can be used only when you have a quantitative variable associated with a list of categories where both the categories and the quantities each add up to a whole.
- The categories must also be disjoint (no overlap)
- Common error: to use a pie chart on a set of categories that do not make a whole and to use a pie chart when the categories overlap.
- Use percentage label when using a pie chart

XY Graphs

- AKA line graph (not necessarily a line)
- used when you have "a lot" of data points
- when categories along the x-axis are numerical
- show trends in data clearly
- enable the viewer to make predictions about the results of data not yet recorded

Bar Graph

- use whenever there is a quantitative variable associated with the a categorical variable
- For limited amount of data
- Succinct
- Easy to make comparisons within categories and across categories
- Disadvantage: sometimes presents far too much info.
- hard to make a single, clear point with them

Guidelines for effective graph:

- a. What is the purpose of making a graph from this data?
- b. What type of graph should you make? pie bar x-y scatter (line)
- c. Decide on a title and consider the the W's (who, what, where and when)
- d. Legend: yes no
- e. Descriptive x-axis label (if applicable)
- f. Descriptive y-axis label (if applicable)
- g. Scale (if applicable)
- h. Source

Faulty Graphs

- People can use graphs to tell you skewed, misleading information.

Example 1

- Go to the qrc homepage. Under excel files, find IL_Pop_By_Race.xls and open it.
- Add a column which contains the percentage of total population for each racial category.
- Make an effective graph.

Guidelines for effective graph:

- a. What is the purpose of making a graph from this data?
- b. What type of graph should you make? pie bar x-y scatter (line)
- c. Decide on a title and consider the the W's (who, what, where and when)
- d. Legend: yes no
- e. Descriptive x-axis label (if applicable)
- f. Descriptive y-axis label (if applicable)
- g. Scale (if applicable)
- h. Source

Example 2

- Go to the qrc homepage. Under excel files, find DePaulMajors04.xls and open it.
- Make an effective graph.

Guidelines for effective graph:

- a. What is the purpose of making a graph from this data?
- b. What type of graph should you make? pie bar x-y scatter (line)
- c. Decide on a title and consider the the W's (who, what, where and when)
- d. Legend: yes no
- e. Descriptive x-axis label (if applicable)
- f. Descriptive y-axis label (if applicable)
- g. Scale (if applicable)
- h. Source

Make your own faulty graph

Change the scale of the y-axis.

Example 3

- Go to the qrc homepage. Under excel files, under the folder Chicago, find ChicagoPopulation1830-2000.xls and open it.
- Make an effective graph.

- a. What is the purpose of making a graph from this data?
- b. What type of graph should you make? pie bar x-y scatter (line)
- c. Decide on a title and consider the the W's (who, what, where and when)
- d. Legend: yes no
- e. Descriptive x-axis label (if applicable)
- f. Descriptive y-axis label (if applicable)
- g. Scale (if applicable)
- h. Source

Example 4

- What is wrong with this chart?

- This week:
- Lab Activity 4
- HW Assignment 3

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