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# Standard deviation watch

1. Hi
I'm a bit stuck on the topic of standard deviation and wonder if anyone might be able to help me?
I have an image of a table which shows the standard deviations of the means of root lengths at different concentrations of sodium chloride.

How can I recognise whether or not these standard deviations overlap? What do I need to do/consider to figure this out?

Thank you. Any help is much appreciated!
2. (Original post by Ggdf)
Hi
I'm a bit stuck on the topic of standard deviation and wonder if anyone might be able to help me?
I have an image of a table which shows the standard deviations of the means of root lengths at different concentrations of sodium chloride.

How can I recognise whether or not these standard deviations overlap? What do I need to do/consider to figure this out?

Thank you. Any help is much appreciated!
It's fairly straightforward- just add and take away the SD value from the mean value to get a range (e.g. for 0 mol dm-3, 20.1-0.38=19.72, 20.1+0.38=20.48). Do this for all the mean values, and see if any of the figures overlap.
3. (Original post by Gnome :))
It's fairly straightforward- just add and take away the SD value from the mean value to get a range (e.g. for 0 mol dm-3, 20.1-0.38=19.72, 20.1+0.38=20.48). Do this for all the mean values, and see if any of the figures overlap.

Thank you so much! You've taken away the SD from the mean, and added the SD to the mean. Are you supposed to do both, or just the part where you take away the SD from the mean (i.e. just the subtraction part) for each concentration?
4. Both- you need to see ge there is any overlap between the ranges
5. (Original post by Gnome :))
Both- you need to see ge there is any overlap between the ranges
Thank you, I really appreciate your help and time! I've done this for all the concentrations so I have 2 numbers for each (products of the subtraction and addition equations), but I'm still unsure what I'm meant to be looking for. What would be an example of an overlap? I'm really sorry to be slow - I struggle a lot with this topic!
6. None of these overlap, so it's fine (there is a significant difference as the concentration changes)

As an example, if you had a result of 19.6 with a SD of +/- 1, and a result of 18.5 with a SD of 0.5, your ranges would be 18.6 to 20.6 and 18 to 19

Can you see that there is an overlap between these ranges?
7. (Original post by Gnome :))
None of these overlap, so it's fine (there is a significant difference as the concentration changes)

As an example, if you had a result of 19.6 with a SD of +/- 1, and a result of 18.5 with a SD of 0.5, your ranges would be 18.6 to 20.6 and 18 to 19

Can you see that there is an overlap between these ranges?
Ah, I get it now! That was a great example . I had no idea before your replies that I had to do anything like this. I can't say how much help you've been. I get so worried when I don't understand these things!

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Updated: March 9, 2013
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