On 27 Oct 2003 17:25:02 -0800, [EMAIL PROTECTED] ([EMAIL PROTECTED]) wrote: [ ... ]
> points. On another test the difference is 12 points. Common sense > tells me there is a significant difference in the two sets of scores > on the test with 12 points difference. My question is: is the > difference of 2 points statistically significant or the result of > chance? If my assumption is correct and one class did significantly > better than the other on one test and on the other the difference in > performance is (probably) not statistically significantly different > then is that a correct assumption? So somewhere between 12 points and > 2 points I can guess there is a significant difference but less than Here is one way to talk about it -- "Is the difference bigger than you would expect by chance? - for samples of the same size, that were randomly chosen." Yes, we casually talk about a difference being statistically significant. That indicates that there is at least a *little* reason for being interested in the difference. There is more reason to be interested, from the start, if the two sets of numbers are something that resulted from an experimental design, with randomization, and the difference is "statistically significant" -- then the DESIGN gives us something to attribute as a possible 'cause.' When the groups are pre-existing, or the difference is something observed that *happens* to exist, it might not be especially interesting to comment that the difference is 'statistically significant.' - It becomes interesting when someone can assert a reason that any difference should *not* exist. > that it is not. I asked a math teacher how to determine that point on > any given set of scores and was told to run a z test. I was told a t > test is used to test whether a sample's mean is representative of the > total population's mean. So I used a z test. In Excel what is > returned is a "z" score, a P score for one tail and a P score for two > tail for a hypothesized mean of .05. Can someone tell me how to > interpret the numbers returned for z, P one tail and P two tail, > assuming the z test is the correct procedure. If not, what do I use > and how do I interpret the results Excel returns? For figuring out one-tailed versus two-tailed testing, read some results after googling < "one-tailed test" FAQ > . That seems to get more relevant pages than < "one-tailed test" tutorial > . -- Rich Ulrich, [EMAIL PROTECTED] http://www.pitt.edu/~wpilib/index.html "Taxes are the price we pay for civilization." . . ================================================================= Instructions for joining and leaving this list, remarks about the problem of INAPPROPRIATE MESSAGES, and archives are available at: . http://jse.stat.ncsu.edu/ . =================================================================
