Thanks for youre response Jay To clarify, the samples are from the same population. I am comparing the mean value and the standard deviation of the number of suppliers that tendered for a contract. The samples are contracts from differenet worktypes. This means that the contracts in the population are grouped arbitrarily by their department. However when I calculated the standard deviations, the confidence interval is non-sensical.
As I know the population mean and standard deviation, I want to compare them to the mean and standard deviation of the samples, however I can't make sense of the data. The mean and standard deviation of the population was 12 and 6.9 so a value 2 standard deviations away would be non-sensical (negative value). Also lets say the mean was 3 suppliers, the standard deviation was 5. Hence the confidence interval would go into negative numbers, which doesn't make sense, as contracts can't have negative suppliers tendering for the contract. Another factor that exasibated the problem was that the range of the values varied greatly. One group of contracts had one contract with 300+ suppliers, and 100+ contracts, whilst another group had only 2 contracts with a range of 10 suppliers. Can I compare these groups? I doubt I can use the empirical rule to standardize the distributions, as I don't know if they are approximately normal. My guess is that because the population and some samples are greatly skewed to the right, it causes these problems. Any help would be greatly appreciated. Phil [EMAIL PROTECTED] (Jay Warner) wrote in message news:<[EMAIL PROTECTED]>... > Could this be a t-test, to compare two samples to see if they indeed come > from the same (or as we conclude) different populations? This would test > for the means of the populations from which the samples came. If so, > then sample size is not an issue. It is a more sensitive test to use > n(1) = n(2), but can be done in any case. > > As for the variances of said samples, one could use an F test to check if > the variances were indeed different. Again, unequal sample sizes are not > an issue. > > That what you have in mind? > > Jay > > philipau wrote: > > > Hi > > > > Sorry if my question seem like a newbie question, but I'm dying to > > know if it is statistically sound to compare the mean and standard > > deviation of different sample sizes from a population. > > > > I know all about the central limit theorum, and how the average sample > > mean will be normally distributed, but I don't know if it is useful to > > compare parameters of different samples that I don't know if they are > > independent or not > > . > > . > > ================================================================= > > Instructions for joining and leaving this list, remarks about the > > problem of INAPPROPRIATE MESSAGES, and archives are available at: > > . http://jse.stat.ncsu.edu/ . > > ================================================================= > > -- > Jay Warner > Principal Scientist > Warner Consulting, Inc. > 4444 North Green Bay Road > Racine, WI 53404-1216 > USA > > Ph: (262) 634-9100 > FAX: (262) 681-1133 > email: [EMAIL PROTECTED] > web: http://www.a2q.com > > The A2Q Method (tm) -- What do you want to improve today? > > > > > . > . > ================================================================= > Instructions for joining and leaving this list, remarks about the > problem of INAPPROPRIATE MESSAGES, and archives are available at: > . http://jse.stat.ncsu.edu/ . > ================================================================= . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
