HELP!!

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HELP!!
Message posted by Paula on January 31, 2001 at 12:00 AM (ET)

I'm back to school after 10 years and trying to take the second have of a statistics class. I need the basics, but don't have the time to study the first 9 chapters of my textbook. Can anyone give me the basics on t and z tests, standard deviation, etc. I just need some easy to understand examples and explainations.

Thanks

READERS RESPOND:
(In chronological order. Most recent at the bottom.)

Re: HELP!!
Message posted by nancy diehl on January 31, 2001 at 12:00 AM (ET)

It's a little hard to give you what you want in 6 words or less, but I'll try to be brief.
1. With a normal distribution your measure of central tendency is the mean and the measure of
dispersion is the standard deviation. The standard deviation is your average amount of scatter
in your data about the mean.
2. t and Z tests are used to test your sample average against a population mean value or another
sample average. Whether you use the t or Z depends upon your sample size. For smaller samples (less
than 30) use the t-test, for larger samples, use the Z. The formulas for the tests
are virtually the same except the t-test uses a t-value from the t-table based on degrees of
freedom. It will be larger than the Z value from the Z-table for the same amount of confidence
because it adds in protection given you are making decisions on a smaller sample size.

Re: HELP!!
Message posted by CY on February 12, 2001 at 12:00 AM (ET)

Standard deviation: a measure of spread.
Normal distribution: shown on a graph as bell shaped.
1 SD: 66% of the population would be within 1 SD from the mean.
2 SD: 95% of the population would be within 2 SD from the mean.

SD can be worked out using three rules, one for grouped data, or you cn use a calculator as well.
t-tests and z-tests are simply what Nancy told you already and I tell you this, SD is very easy, don't worry about it!

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