Reading Graphs Critically

Learn graph scales, relative frequency.

Lesson 3 of 32 parts Practice Flashcards

1/2

Graph Scales

Objective: Explain graph scales, apply the stated method, and check its conditions.

Graph interpretation requires axis labels, units, baseline, and scale intervals. A truncated bar-chart baseline can exaggerate apparent size ratios even when endpoint values are accurate. Calculate actual differences from the numerical scale before making a comparison. Visible bar-length ratios can mislead when the baseline is not zero.

Formulas

Actual difference = value₂−value₁

Worked examples

Try itA bar-chart axis starts at 7 rather than zero. Bars end at 14 and 21. Find the actual numerical difference between the values.Show answer

Step 1: Read numerical endpoints rather than judging drawn bar lengths. Step 2: Difference=(21)−(14). Step 3: The actual difference is 7; a truncated axis can exaggerate its appearance.

Swipe sideways to move between sections

Graph Scales

Objective: Explain graph scales, apply the stated method, and check its conditions.

Formulas

Actual difference = value₂−value₁

Worked examples

Try itA bar-chart axis starts at 7 rather than zero. Bars end at 14 and 21. Find the actual numerical difference between the values.Show answer

Step 1: Read numerical endpoints rather than judging drawn bar lengths. Step 2: Difference=(21)−(14). Step 3: The actual difference is 7; a truncated axis can exaggerate its appearance.

Relative Frequency

Objective: Explain relative frequency, apply the stated method, and check its conditions.

A category’s relative frequency is its count divided by the total observational count. For nonoverlapping exhaustive categories, these fractions sum to one. Distinguish counts from proportions and verify that the reference total matches the group being described. Use the relevant total and nonoverlapping categories.

Formulas

Relative frequency = category count / total count

Worked examples

Try itA synthetic frequency table has 42 cases in one category and 91 total cases. Find that category’s relative frequency.Show answer

Step 1: Relative frequency is category count divided by total. Step 2: Use 42/91. Step 3: The relative frequency is 6/13.

You finished the reading!

Lock it in with a few practice questions. This is the last lesson in the chapter.

Practice

Previous lessonPopulations and Samples

Last lesson