Reports and Visualizations

Real Limits, Apparent Limits and Frequency Distributions

Recall that a continuous variable has an infinite number of possible values. It can be represented by a number line that is continuous and has an infinite number of points. However, when we measure a continuous variable we have only a finite measurement process, resulting in numbers that have a finite precision.
If our measurements of a continuous variable are all numbers that are all in whole integer units, our precision of measurement is 1 unit. In this measurement situation, an observed value of 8 would be obtained when the "real value" is 7.8 or 8.21, or any other value between 7.5 and 8.5. Thus, the observed value of 8 actually represents a range of "real values" from 7.5 to 8.5. These values are called the "real limits".
The concept of "real limits" also applies to class intervals. In the table at the right the interval denoted as "60-64" actually has "real limits" of 59.5-64.5. The values denoting the interval as 60-64 are called the "apparent limits". Back