The Professor's Response
I have a question on Class Width. When you use the formula to find it and get a whole number like 7, for example, do we have to add a decimal point after like 7.1 or 7.5 or can we round up to 8? Thank you !
See the professor's answer below.
If there is a small number of classes involved (for example, just five classes), it is usually best to go to the next highest whole number. That means you can go from 7 to 8 safely, but you should always check. For example, say we have a maximum value of 40 and a minimum value of 5, and we would like to have a table with five classes. The smallest class width that could work is (40 - 5)/5 = 35/5 = 7. When we check 7, we can see it doesn't work:
5 - 11
12 - 18
19 - 25
26 - 32
33 - 39
Notice that 40 (our largest value) does not fit into the last class. This means we can try 8 instead.
5 - 12
13 - 20
21 - 28
29 - 36
37 - 44
Notice that now 40 fits nicely into our last class. This will usually work well, unless you have many classes. If you have 18 classes, going from 7 to 8 would probably not work out too well. Usually, with that many classes, the last two or three classes are empty if you use a width of 8 when the calculation yields a value of 7. It is in those situations that it becomes necessary to use a decimal like 7.1 or 7.2.
Here is another post on the topic if you need more information: