Averages & Interpreting Data
Find averages from frequency tables, estimate the mean of grouped data, and compare data sets.
Overview
Year 9 statistics moves from raw lists to organised data. Students find the mean, median and mode from frequency tables, estimate the mean of grouped data, and compare two sets of data using an average and the range. Interpreting data well is a major part of IGCSE statistics.
What You Will Learn
- Find the mean, median, mode and range of a small data set
- Find averages from a frequency table
- Estimate the mean of grouped data using midpoints
- Compare two data sets using an average and the range
- Choose the most appropriate average for a situation
Key Vocabulary
Common Mistakes to Avoid
- Forgetting to multiply value × frequency when finding the mean from a table
- Using the class width instead of the midpoint for grouped data
- Dividing by the number of classes instead of the total frequency
- Confusing the range (a measure of spread) with an average
What Comes Next
At IGCSE this develops into cumulative frequency, histograms, and more formal comparison of distributions, within the Statistics topic.
Frequently Asked Questions
How do I find the mean from a frequency table?
Multiply each value by its frequency, add these products to get the total, then divide by the total frequency (not the number of rows). This is sometimes written as Σfx ÷ Σf.
Why is the mean of grouped data only an estimate?
Because grouped data only tells you the class each value falls in, not the exact values. You use the midpoint of each class as a representative value, so the mean you calculate is a sensible estimate rather than an exact figure.
Study This Topic
Topic Details
- Stage
- Year 9
- Strand
- Statistics and Probability
- Framework ref
- 9Ss
- Difficulty
- Medium
Build strong foundations in Averages & Interpreting Data
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