Difference between revisions of "Documentation/How Tos/Calc: ZTEST function"
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:: [[Image:Calc_z_formula.png]] | :: [[Image:Calc_z_formula.png]] | ||
| − | : where ''m'' is the sample mean and ''n'' the number in the sample. | + | : where ''m'' is the sample mean and ''n'' the number in the sample. When the mean and standard deviation of the population are known, the z statistic forms a standard normal distribution - that is, a normal distribution with mean=0 and standard deviation=1. |
| + | |||
| + | : <tt>'''ZTEST'''</tt> returns the '''one-sided''' cumulative probability - the area under the standard normal curve to the right of the z value (shaded blue here): | ||
| + | <center>[[Image:Calc_ztest_graph2.png]] [[Image:Calc_ztest_graph1.png]] </center> | ||
=== Example: === | === Example: === | ||
Revision as of 08:53, 20 July 2008
ZTEST
Returns the result of a z-test.
Syntax:
ZTEST(data; μ σ)
- data is a range or array containing a random sample from a population (population assumed to have a normal distribution).
- μ is the (known) mean of the population.
- σ is the (known) standard deviation of the population. If omitted, it is estimated from the sample data by STDEV(data).
- ZTEST calculates the z statistic:
-
- where m is the sample mean and n the number in the sample. When the mean and standard deviation of the population are known, the z statistic forms a standard normal distribution - that is, a normal distribution with mean=0 and standard deviation=1.
- ZTEST returns the one-sided cumulative probability - the area under the standard normal curve to the right of the z value (shaded blue here):
Example:
ZTEST(A2:A20; 9; 2)
- returns the result of a z-test on a sample A2:A20 drawn from a population with known mean 9 and known standard deviation 2.
See also:
Issues:
- The validity of this measure is not clear; see for example the draft ODFF standard 16May08, and that Excel has referred to this as both a one-tailed and a two-tailed test.
- Calc and Excel produce different results for the 3 parameter version of this function. Excel calculates 1 - NORMSDIST(z). See issue 90759.
