The midpoint of each class interval is called the class midpoint and is sometimes referred to as the class mark. It is the value halfway across the class interval and can be calculated as the average of the two class endpoints.

                                            

Unemployment Rates for France Over 40 Years 1.6 2.1 4.2 8.6 9.6 1.5 2.7 4.6 10 10.4 1.2 2.3 5.2 10.5 11.8 1.4 2.5 5.4 10.6 12.3 1.6 2.8 6.1 10.8 11.8 1.2 2.9 6.5 10.3 12.5 1.6 2.8 7.6 9.6 12.4 1.6 2.9 8.3 9.1 11.8

Frequency Distribution of the Unemployment Rates of France Class Interval Frequency 1-under 3 16 3-under 5 2 5-under 7 4 7-under 9 3 9-under 11 9 11-under 13 6

Relative frequency is the individual class frequency divided by the total frequency.

 

The relative frequency for the class interval 3-under 5 is Frequency/Total Frequency, i.e. 2/40 = 0.050.

Cumulative Frequency

The cumulative frequency is a running total of frequencies through the classes of a frequency distribution. The cumulative frequency for each individual class interval is the frequency for that class interval added to the preceding cumulative total. For the first class, the cumulative frequency is simply the same as the class frequency.

 

The cumulative frequency is the running count up to, and including, the frequency of the current class interval.

 

In the table below, the cumulative frequency for the first class interval is simply the Frequency (16) as there is no preceding cumulative frequency. The cumulative frequency for the second class or interval is the Frequency of the second class plus the cumulative frequency of the first interval/class (16 + 2 = 18).

 

The above process continues through the last interval, at which point the cumulative total equals the sum of the frequencies (40).

 

Interval	Frequency	Class Midpoint	Relative Frequency	Cumulative Frequency
1-under 3	16	2	0.400	16
3-under 5	2	4	0.050	18
5-under 7	4	6	0.100	22
7-under 9	3	8	0.075	25
9-under 11	9	10	0.225	34
11-under 13	6	12	0.150	40
Totals	40		1.000