Overview
This lecture explains how to create a grouped frequency distribution table for a dataset, determining appropriate class widths, limits, and calculating frequencies and relative frequencies.
Determining Range and Class Width
- Find the range by subtracting the smallest value from the largest (e.g., 47 - 3 = 44).
- Use the Excel
MAX() and MIN() functions to find the largest and smallest data values.
- Divide the range by a suitable number of classes (usually 5–20, often 10) to estimate class width.
- Round class width to a "nice number" (whole numbers like 5 or 10 are preferred).
- The goal is to have each class (group) cover equal-width intervals.
Setting Class Limits
- Start the first class at the largest multiple of the class width less than the smallest value in the data.
- Each class should be non-overlapping (e.g., 0–4, 5–9, etc.).
- The upper limit of one class is just below the lower limit of the next; avoid overlap (a value belongs to only one class).
- Continue adding classes until the maximum data value is included.
Creating the Frequency Table
- List class intervals and count how many data points fall in each (frequency).
- Use Excel's count feature to tally frequencies quickly.
- Sum all frequencies and check this total matches the sample size to avoid errors.
Calculating Relative Frequency
- Add a column for relative frequency (frequency divided by sample size).
- Use absolute referencing in Excel formulas to ensure correct calculations.
- Relative frequencies should sum to 1; can be shown as percentages if preferred.
Key Terms & Definitions
- Frequency Distribution Table — a table that shows the number of data points (frequency) in specified intervals (classes).
- Range — the difference between the largest and smallest values in the dataset.
- Class Width — the size of each group or interval in the table.
- Class Limits — the lowest and highest values that can go into each class.
- Relative Frequency — frequency of a class divided by the total number of data points.
Action Items / Next Steps
- Practice creating a grouped frequency distribution table using sample data in Excel.
- Prepare to learn about creating histograms and bar graphs in the next lesson.