Unit 5: Statistics
Topic A: Line Graphs
Line graphs are used to show changes that happen over a period of time. Line graphs easily show trends and patterns.
The most common way to set up a line graph is to put time on the horizontal (x) axis. Whatever is being measured is then put on the vertical (y) axis.
Graph 1
Leah has taken up cycling and jogging to improve her cardiovascular fitness and for weight control. She takes her pulse every Monday morning before she gets out of bed; that is her basal heart rate. Graph One records Leah’s heart rate for the first 12 weeks of her exercise program.
- What is the title of the graph?
- What is being measured on the vertical axis?
On this particular graph the vertical scale is one heartbeat per line. The scale on the horizontal axis is one week per line.
- What was Leah’s basal heart rate on the fourth week of her exercise program?
- Find Week 4 on the horizontal (x) axis.
- Look straight up from Week 4 until you come to the point in the graphed line.
- Now look at the scale on the vertical (y) axis. Lay a ruler or straight piece of paper across the graph to help you read the scale at the point for Week 4.
Leah’s basal heart rate was 74 beats/min in week four.
- Find her basal heart rate in Week 7.
- What does the graph show us happened between Week 9 and Week 10?
- What trend does this graph show?The graph shows Leah’s basal heart rate is “going down” or decreasing.
Often, you need to estimate the value of the point in the graphed line. Look at Graph Two which has Leah’s same heart rates recorded.
Answers to Graph 1
- Leah’s Weekly Basal Heart Rate
- Heart beats per minute
- Given: 74 beats/min
- 71 beats/min
- Leah’s heart rate went up from 68 to 69 beats/min
- Given: Leah’s basal heart rate is “going down” or decreasing
Graph 2
Now the scale on the vertical axis is five heartbeats per line. Use a straightedge (ruler or paper) across the graph to help you read the vertical scale.
- Give Leah’s heart rate in Week 5.
- Give Leah’s heart rate in Week 10.
- What was Leah’s heart rate in Week 12?
- Using the information on the graphs, tell how much Leah’s basal heart rate decreased (in beats per minute) from Week 1 to Week 12.
Answers to Graph 2
- 75 beats/min
- 69 beats/min
- 67 beats/min
- Decreased 11 beats/min (78 – 67 = 11)
The person drawing a graph decides how to label it and how to write the scale on the axes depending on the information to be shown on the graph. The graphs about Leah focus on the range of her heart rate. There is no need to make the heart rate scale lower than 55 or higher than 80 for Leah.Graphs often show information about several things on the same graph. Such graphs are very useful for making comparisons. Look for a legend or key that explains what each graphed line represents. The legend may be printed right by the graphed information or it may be beside or below the graph.
Graph 3
Leah’s husband John decided he would exercise as well. He had a rapid heart rate at the beginning