Enjoy learning Statistics Online! Please be sure to share and subscribe to our YouTube channel.
ASK THE PROFESSOR FORUM
Course Documents
Chapter 1 - Intro
Chapter 2 - Methods for Describing Sets of Data
Chapter 3 - Probability
Chapter 4 - Discrete Random Variables
Chapter 5 - Normal Random Variables
Chapter 6 - Sampling Distributions
Chapter 7 - Confidence Intervals
Chapter 8 - Tests of Hypothesis: One Sample
Chapter 9 - Confidence Intervals and Hypothesis Tests: Two Samples
Sample Exam I: Chapters 1 & 2
Sample Exam II: Chapters 3 & 4
Sample Exam III: Chapters 5 & 6
Sample Exam IV: Chapters 7 & 8
Hello Professor,
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 !
Posted to on Monday, January 27, 2014 Replies: 1
Hi Martina,
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:
http://www.statsprofessor.com/atpquestion.php?qid=102
Professor McGuckian