standard deviation N or N--1?

[dilinim]

Hi,

So I am really confused as to what to use for the standard deviation on the dat. Is it N-1 or N?? Chad says N-1 because it is a small population, but the math destroyer has just N.

What do we use on the real dat??!

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[coheedutk]

My experience so far (destroyer 2011 and math destroyer),is that you can tell from the answer choices, if two ( maybe three) can't be distinguished subtract the largest from the smallest, until you see one answer that has a larger difference.

 

[Ari Rezaei]

The N and N-1 come from sample vs. population standard deviations.

N-1 is a conceptual thing from degrees of freedom in stats, thats why when we are taking a sample from a large population we use N-1.

If we know the exact values of the entire population and don't need a sample (because we already have all the data points), then we don't need to go down that route and just use N.

I don't think the real DAT will try to trick you on this. If the problem mentions a "sample" then use N-1. If it just gives you a set of numbers, use N. In either case, one of them should give you the answer, the other shouldn't be in the choices.

 

[dilinim]

Thanks! that helps a lot!!

 

[H4LfAd1ME]

The N and N-1 come from sample vs. population standard deviations.

N-1 is a conceptual thing from degrees of freedom in stats, thats why when we are taking a sample from a large population we use N-1.

If we know the exact values of the entire population and don't need a sample (because we already have all the data points), then we don't need to go down that route and just use N.

I don't think the real DAT will try to trick you on this. If the problem mentions a "sample" then use N-1. If it just gives you a set of numbers, use N. In either case, one of them should give you the answer, the other shouldn't be in the choices.

Hi Ari,

I know this forum is really old, but I came across it when I got stuck and got even more confused by your answer. I think you switched the n and n-1. I learned it as use n-1 for SAMPLES and use n for populations. Can you verify? All the other forums regarding this say the opposite.

 

[TheEpicFruitCake]

Hi Ari,

I know this forum is really old, but I came across it when I got stuck and got even more confused by your answer. I think you switched the n and n-1. I learned it as use n-1 for SAMPLES and use n for populations. Can you verify? All the other forums regarding this say the opposite.

Doesn't he say n-1 is samples?

 

[H4LfAd1ME]

Doesn't he say n-1 is samples?

Wait, a sample is a set of numbers, which is what n-1 would be used for. But Ari also says if a set of numbers are given, n would be used. But a set of numbers = a sample, isn't it?