Calculating the difference between two population means

[Demetri]

Hi I am working on a question and I need some help.

Question
Is their sufficient evidence to indicate a difference in mean serum uric acid levels between normal individuals and individuals with Downs's syndrome. the data consist of serum uric acid readings on 12 individuals with Down's syndrome and 15 normal individuals. The means are x̄1 is 4.5 mg/100 ml and x̄2 is 3.4 mg/100ml.

I am trying to find the standard deviation of the sample, how can I do this ? I dont have the population standard deviation.
Thanks

 

[hlsmith]

I would be curious what the distributions of the two sample groups are for the outcome given this is a lab value. This may dictate whether a mean is appropriate and which test to use.

Also, are you referencing the sample groups std or the pool sample?

 

[Demetri]

I am assuming that the samples were drawn from a normal distribution. The question did not say. I would need to find the sample std. and not the polled sample. If I have either the sample or population std then I can solve problem by using the test statistics for (difference of means) small independent samples

 

[hlsmith]

So your questions is how do you compare them without a measure of dispersion? And you were not given this information?

 

[Demetri]

You are correct. The measure of dispersion was not given.

 

[hlsmith]

If you have the data why don't you calculate them?

 

[Demetri]

Hi. I don't have the data. The question I pose was from a problem worksheet.