Grouped Discrete Data
Recall that in a grouped discrete data, the data are usually whole numbers. Also, in grouped discrete data, the intervals do not overlap. So it is inappropriate to use such intervals. However, when we group discrete data, we are actually treating it as though it was continuous.
Grouped Continuous Data
When using data that are continuous, the variable is measured on a continuous scale. Note that for continuous data, we use the class boundaries and not the class intervals.
Class Limits: Given a class interval of 40 – 44, the number 40 is the lower class limit, while the number 44 is the upper class limit.
Class Boundaries: Given a class interval of 45 – 50, the class boundaries become 44.5 – 50.5
That is to obtain the lower class boundary subtract 0.5 from the lower class limit.
Mid-Class Value (Class Mark)
The Mid-value of a class is known as the class mark. For instance, the mid-class value is exactly half way between the lower limit and the upper limit. For example the mid-class value for 39.5 – 45.5 is given as
\( \frac{39.5 + 44.5}{2} \scriptsize = 42.5 \)
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