Talk:Z-test
From Wikipedia, the free encyclopedia
 |
This article is within the scope of WikiProject Statistics, which collaborates to improve Wikipedia's coverage of statistics. If you would like to participate, please visit the project page. |
 |
|||||||||||||||||||||||
| Mathematics rating: | Start Class | Mid Priority | Field: Probability and statistics | ||||||||||||||||||||
| One of the 500 most frequently viewed mathematics articles. | |||||||||||||||||||||||
|
|||||||||||||||||||||||
Hi all,
in the line "a mean score of 96 is -2.47 standard deviation units from the population mean", shouldn't it say "standard error units"? I'm not sure about this, so if you know for sure, please change or don't.
Regards WikiBasti 12:16, 25 November 2005 (UTC)
This sentence in the article: "What this tells us is that 49.32% plus 50% or 99.32% of the students who took the test scored better than did the fifth grade students in our sample" is misleading. It's not true that 99.32% of all students do better: what's true is that 99.32% of the time, a randomly selected group of 55 students have a higher average score than these 55 students had. MvH Jan 16, 2006.
Contents |
[edit] Two-sided test
I think it should be clarified at the bottom of this article that this is a two-sided test as opposed to a one-sided test.
[edit] Simple random sample
The article states that the sample must be a simple random sample from the population, but I can't make sense of this. Isn't this the null hypothesis, and consequently, isn't the test only meaningful if the sample is NOT random? The test is used to see if the sample that you drew from the population behaves like a simple random sample...it's only interesting if it doesn't -anon
[edit] Error in article?
Reject null hypothesis? Shouldn't the null hypothesis be rejected in the example since the Z score of -2.47 is outside the 5% confidence interval?
"In the case of our sample mean, the z score of −2.47 which provides us a value of 49.32% means that 49.32% plus 50% or 99.32% of the population scored closer to the population mean than did our sample of students. Since our sample is outside of this area by 1.82%, we can't reject the null hypothesis because the value of 1.82% is less than 5%, our confidence level.
Therefore we can conclude with a 95% confidence level that the test performance of the students in our sample were within the normal variation."
It looks like whoever wrote the above is confusing tail probability and the z-test.
[edit] Error Regarding Population Standard Deviation and Sample Standard Deviation?
In the formula under "First calculate the standard error (SE) of the mean:" shouldn't the sigma instead be 's'? I believe the question here is whether your value falls into your estimated confidence based on your sample. I am not sure what the population standard deviation is used here. I am not certain about this, but it seems intuitively wrong to me The Sleepwalker (talk) 07:11, 5 June 2008 (UTC)
203.143.164.204 (talk) 03:12, 2 April 2008 (UTC)
