Q.Explain the following terms used in a continuous frequency distribution: class limits, class interval (width), class mid-point, and the difference between the exclusive and inclusive methods.

A continuous frequency distribution groups values into class intervals, each described by a small set of standard terms.

In a continuous frequency distribution, values are grouped into class intervals, described by these terms (illustrated on the class 0–10, next class 10–20):

• Class limits — the two end-values of a class. The smaller (0) is the lower limit, the larger (10) the upper limit.
• Class interval / class width (h) — the difference between the upper and lower limits: here 10 − 0 = 10.
• Class mid-point (mid-value) — the average of the two limits, (lower + upper)/2 = (0 + 10)/2 = 5; it represents the whole class in later calculations (e.g. computing a mean).
• Frequency (f) — the number of observations falling in the class.

Exclusive vs inclusive methods:

A frequent error is computing the mid-point as the upper limit alone, or the width as the mid-point — the mid-point is (lower + upper)/2 and the width is (upper − lower). Another is forgetting that an incl …