Standard deviation

[sam0001]

How do you guys go about estimating the standard deviation for box plots? I tried the rule from the essential textbook
Range/4, didn't get me the right answer!

[brenden]

How do you guys go about estimating the standard deviation for box plots? I tried the rule from the essential textbook
Range/4, didn't get me the right answer!

It's range /6. Dunno what the textbook is on about.

[Stick]

I happened to ask my teacher about this the other day - his answer really clears up a lot of the confusion expressed here.

If the question states the data is normally distributed, you need to divide the range by six. However, if it does not state the nature of the data's distribution, then you divide the range by four. Both are only estimations at best, but it explains why there are two formulae floating around.

[sam0001]

So basically, for a symmetrically distributed boxplot, I would use the range/6

But for a positively skewed or negatively skewed, range/4?

[Stick]

Yeah, although due to the general confusion I doubt it will be on the exam.