Grouped Data / Interval Data
Big Idea: When we have a large set of numerical data, organizing individual values becomes impractical. Instead, we group the data into intervals (also called classes) and analyze the distribution using these groups.
What is Grouped Data?
Grouped data is data that has been organized into groups called class intervals. Each interval covers a range of values, and we count how many data points fall into each interval. This count is called the frequency.
Key Vocabulary
| Term | Definition | Example |
|---|---|---|
| Class Interval | A range of values that groups the data | $10 - 19$, $20 - 29$, $30 - 39$ |
| Lower Class Limit | The smallest value in an interval | In $10 - 19$, it's $10$ |
| Upper Class Limit | The largest value in an interval | In $10 - 19$, it's $19$ |
| Class Width | The difference between consecutive lower limits | $20 - 10 = 10$ |
| Class Mark (Midpoint) | The middle value of an interval | $\frac{10 + 19}{2} = 14.5$ |
| Frequency ($f$) | The number of data values in each interval | If 7 scores are between 10–19, $f = 7$ |
| Cumulative Frequency | Running total of frequencies | Sum of all frequencies up to that interval |