Comparison of Statistical Diagrams

 

What Does It Mean to Compare Statistical Diagrams?

When comparing graphs or charts for different groups or data sets, we’re looking at:

• Trends — Is the data increasing, decreasing, or staying the same?
• Peaks and dips — Where are the highs and lows?
• Spread — How much variation is there?
• Averages — What’s the typical value?

You might be comparing:

• Two bar charts
• Two line graphs
• Two pie charts
• Or even mixed diagrams, like a pie chart vs. a bar chart

 

How To Compare Diagrams Step-by-Step

1. Read the question carefully
   • Know who or what is being compared.
2. Check the scales and axes
   • Are both diagrams using the same units?
3. Use numbers to back up your points
   • Refer to actual values or ranges from each diagram.
4. Look at the shape and pattern
   • Are there steep rises? Flat sections? Sudden drops?
5. Mention any outliers
   • These are values that stand out or don’t fit the trend.
6. Calculate averages and spread if needed
   • Mean, median, mode = average
   • Range = measure of spread
7. Explain what the comparison shows in context
   • Don’t just say “the range is bigger” — explain what that means in real life.

 

Example

A local cinema tracks the number of snacks sold to teens and adults over 5 days. The data is shown in a dual bar chart.

(a) Describe how snack sales to teens changed over the 5 days.

Look at the heights of the teen bars only.

Snack sales to teens increased from 20 on Monday to 35 on Friday, with the biggest rise between Wednesday and Thursday.

(b) A manager says, “Adult snack sales were more varied.”

Use a statistical measure to test this.

Let’s compare range (largest - smallest):

• Teens: 35 - 20 = 15
• Adults: 40 - 30 = 10

The teen sales had a larger range (15 > 10), which means teen snack sales were actually more varied than adult sales. The manager’s claim is incorrect.

(c) Why might this data not be reliable for making decisions?

The data only shows one week, so it may not reflect regular patterns.

For example, there might have been a holiday or promotion that affected sales.