### Dispersion diagrams

I am actually studying/revising for my 'Advanced Higher' geography exam - this is not dissimilar to A-Level as we consistently use their set texts. It is the Scottish equivalent, and the Statistical part of the course involves a question on a particular method of stat. testing in the final exam paper.

I cannot read dispersion diagrams! I am quite a logical person, but the texts seem to use fancy words which just confuse me, and I am worried that a question on one will arise in my exam this year.

I would appreciate any note/hints/tips/easy-step-by-step guides which u could offer me on 'Statistical Awareness' concerning 'Dispersion Diagrams' and how to make sense of them.

Thank you!

Imagine you and your class could see your Higher results now!

You are all sat in your Geography room and you all have to be coloured with 4 colours according to how well you have done! How do you decide how many of you get shaded which colour?

It's nearly always 4 colours, because dispersion diagrams usually talk about 4 "quartiles". There can be quintiles or terciles, but in your exam, pound to a penny it will be quartiles. Your chief examiner probably doesn't understand anything more difficult than quarters!

No-one has got 100%, no one has got 0%, but everyone ranges from, say 32% to 88%. Say there are 31 of you.

The difference between top and bottom is 56%, right.

Plot all the %s as dots on a scale line, from 0-100%. This gives you your "dispersion diagram - really, that's all dispersion diagrams are, dots on a line. If 3 people have got 65%, you plot 3 dots next to that value.

You are usually asked to do some simple maths with the data.

A. Find the mean. I'm sure you'd cope!

B. Find the Median. (Higher Level maths-in-Geography is not too hard, eh?)

C. Find the range of values i.e. the difference, see above, duh!

D. Identify the "quartiles" Aha! A slight difficulty! How many of you
are there - 31. That's ABOUT 8 in each quartile; you really don't have to be any
more accurate than that. Stick 7 in one and 8 in all the rest. Draw lines to separate
your quartiles. Name them: upper, upper middle, lower middle and lower quartiles.
Your median value should come between the middle two. Give each quartile one of
the 4 colours. Now colour your geography group cleverly, with darker colours for
the best performers and you have a chloropleth map for your class, based on quartiles.
You, of course are a black!

The only statistical awareness you have to show here is a little bit of very simple maths. Statisticians often dress up their art in a complex way to make it look good. It's not complex. It's easy and VERY useful! I'll bet you quote statistics in your future career a lot and it really pays to understand them, 'cos others won't and your bosses will try to blind you with them.

Hope this helps, any other revision probs, get back to me.