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Results tagged with z-test
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user 805
The z-test is a statistical test for hypothesis testing that uses the standard normal distribution as the sampling distribution of the test statistic. A common example is the test for the difference of two proportions.
8
votes
Accepted
Wald Test and Z Test
Some people call both "the Wald test".
See, for example, Wikipedia on the Wald test. Note that if you square the Z statistic you get the chi-square statistic; similarly the square of the two tailed …
- 290k
2
votes
Which statistical test should I use to compare two samples?
My data points represent the percentage of tests failed all throughout high school in both groups.
This looks like count data; you'll likely have variance changing as the mean changes, skewness, …
- 290k
1
vote
Accepted
What do the remaining columns (after column 2) in a Z table mean
All of the columns are probabilities of the sort you mean.
The table is organized so that you can look up your z-values to two decimal places.
For example, to look up the value 1.42, you look down t …
- 290k
6
votes
What happens if I use Z-test instead of T test?
Because the critical values are smaller with the Z, the rejection region is larger.
So yes, significance level goes up, and consequently the rest of the power curve comes with it, as it does whenev …
- 290k
1
vote
Accepted
p-values in sign test
Not all books do this, of course -- many books specifically for statistics students, for example, discuss this properly.
However, you're correct that a lot of basic books designed for students in var …
- 290k
4
votes
Not able to understand the intuition behind $z$-test, $t$-test
Say we want to test if a particular thing holds true on a population or not,
This does sound like the sort of thing people tend to use hypothesis testing for.
say mean of content weights in …
- 290k
1
vote
Appropriate use of z test comparing two proportions
1) Your data look to be paired. You shouldn't ignore this
2) The usual proportions test assumes a constant 'success' rate across observations (the things you're testing the algorithms on). This doesn …
- 290k
13
votes
Accepted
chi squared test or Z test?
Yes, it's possible to do a chi-square test on this.
Specifically, this is the chi-square goodness of fit test. To do it correctly you set up two cells (one for dead, one for not dead), like so:
…
- 290k
1
vote
Hypothesis testing - speeds before and after
It seems to me that usually with timings you'd be expecting (and interested in detecting) scale shifts. This would corresponding to looking at the percentage faster or slower.
As such, a location-shi …
- 290k
2
votes
Why t-test of correlation coefficient can't be used for testing non-zero?
Short answer: You don't use a t-test of the depicted form when $\rho\neq 0$ simply because the statistic $\frac{r\sqrt{n-2}}{\sqrt{1-r^2}}$ has a $t_{n-2}$ distribution when $\rho= 0$ (and the other a …
- 290k
4
votes
Accepted
How do we perform a two-tailed z-test when we *do* know the population mean of the intervent...
I just watched the first part of that. That ... worries me.
Short answer: Unless more context than I just had drastically alters what they're doing there, then you're right in thinking that they're w …
- 290k
5
votes
Why is independence required for two- sample proportions z test?
All participants answered two questions. One question was answered correctly by 85% and the other question was answered correctly by 65%. I am interested in whether the proportion of correct answer …
- 290k
1
vote
One sample t test or one sample z-test
Imagine we have the following situation:
A previous sample of size $m$, from which we have an estimate $s^2_m$ of its population variance $\sigma^2$. (Here the $m$ subscript is simply denoting the si …
- 290k
4
votes
$2\times2$ contingency table: z or t test (aka $\chi^2$ or F test)
You seem to be relying on an ad hoc argument that if the standard deviation of some population distribution is unknown, then if we have a statistic of the form:
$$\frac{\langle\text{estimate of mean}\ …
- 290k
6
votes
Accepted
Why does the proportions_ztest function in statsmodels produce different values than the for...
proportions_ztest seems to work exactly as documented.
Unfortunately what the documentation says it does is just not what you're expecting it to do.
By default this function uses the sample proportion …
- 290k