Setting a consistent class width across groups gives each group equal parameters. This is important when you’re making a frequency distribution table, since you want to show how the items (numbers) are distributed among equal segments of the entire range.
Setting a consistent class width across groups gives each group equal parameters. This is important when you’re making a frequency distribution table, since you want to show how the items (numbers) are distributed among equal segments of the entire range.
Items (e. g. , grades): 64, 68, 73, 75, 78, 79, 81, 83, 83, 84, 89, 90, 91, 94, 96, 97 Largest item (97) minus smallest item (64): 97-64=33 Range: 33
Items (e. g. , grades): 64, 68, 73, 75, 78, 79, 81, 83, 83, 84, 89, 90, 91, 94, 96, 97 Largest item (97) minus smallest item (64): 97-64=33 Range: 33
In our example of number grades, there are 16 items. Since this is fewer than 20 items, we’ll follow the “rule of thumb” and use 5 classes.
In our example of number grades, there are 16 items. Since this is fewer than 20 items, we’ll follow the “rule of thumb” and use 5 classes.
You’ll often see the “class width formula” defined as (max-min)/n, with “(max-min)” representing the range calculation and “n” referring to the number of classes.
You’ll often see the “class width formula” defined as (max-min)/n, with “(max-min)” representing the range calculation and “n” referring to the number of classes.
NOTE: In some cases you may prefer for the first (lowest) and/or last (highest) classes to extend beyond the smallest or largest item. You might, for example, want the first class to start at 60 (or even 0) instead of 64, and the last class to end at 100. This is generally fine to do if it suits your needs.
The first class starts at 64. 64+7 (class width) =71 (start of second class). Since 71-1=70, the first class includes all items between 64 and 70. NOTE: If you choose to start the first class at 60, 0, or any other number, be sure to do this calculation with 64 as your starting point.
64-70 71-77 78-84 85-91 92-98
64-70: 2 items (64, 68) 71-77: 2 items (73, 75) 78-84: 6 items (78, 79, 81, 83, 83, 84) 85-91: 3 items (89, 90, 91) 92-98: 3 items (94, 96, 97) Note: If you’re asked to calculate the relative frequency for the items in each group, divide the number of items in each group by the total number of items. For example, the relative frequency for the first group is 2/16 or 0. 125.
88-8=80
8+12-1=19, so the first class goes from 8 to 19.
8-19 20-31 32-43 44-55 56-67 68-79 80-91
8-19: 3 items (8, 11, 17) 20-31: 3 items (21, 22, 30) 32-43: 4 items (35, 37, 40, 42) 44-55: 3 items (44, 46, 55) 56-67: 2 items (57, 63) 68-79: 5 items (69, 71, 75, 78, 79) 80-91: 2 items (84, 88)
In an open cell you want to use for class width (e. g. , cell D1), enter Excel’s “roundup” function, which automatically rounds up the result to the next whole number: =ROUNDUP() Using Excel format, enter the class width formula inside the parentheses of the “roundup” function in D1: =ROUNDUP((MAX(B1:B16)-MIN(B1:B16))/5) You’ll get the following (correct) class width result in D1: 7 Note that this process also works in Google Sheets.
