The z-test is a statistical test for hypothesis testing.

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Comparing differences of ratios in 2 independent populations

I have a setting that I think is quite similar to the one described in What type of statistic should I use to compare ratios in my experiment?. I have two independent populations, which were screened ...
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27 views

Z-test with a lot of null values

I have a question concerning the validity of my email tests. I'm testing different email variations (between 2 and 4 variations usually) with different groups of members (hundreds of thousands ...
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30 views

Strange two sample z test result in experiment

I performed an experiment on a virtual population wanting to see whether Vitamin C can positively affect performance on an IQ test. I gathered 80 people and grouped them into two groups of 40. ...
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34 views

Deriving the power formula of the one-sample proportion test

I have to derive the power of the z-test in testing $$ H_0: \pi=\pi_0 \text{ versus } H_1: \pi>\pi_0 $$ Denoting by $p$ the sample proportion, the power equals $$ ...
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Is there a t-test equivalent to Stouffer's z-test?

I have k pairs of samples from different distributions. For each pair of samples I want to check if the samples are taken from a normal distribution with the same mean and variance. I assume the ...
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126 views

“The test statistic is reported as a z…”

I was reading a neuroimaging paper in which the authors compare the effect of a chemical compound on a measure of brain connectivity. They measure the value of connectivity for each brain voxel under ...
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31 views

1 sample z test of proportions

We are trying to work out whether what we currently do is accurate. We want to work out if a proportion (% scoring 5 on a 5 point scale) are significantly below a target score. Normally a 1-sample ...
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65 views

Significance of continuous variables

I have a table with several numerical continuous measurements and an indicator column catastrophy ...
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43 views

Statistics on tastings

Some people at my workplace have had some fun lunch discussion as of late, concerning some people's alleged ability to taste the difference between things one thought one shouldn't be able to taste a ...
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155 views

Why is independence required for two- sample proportions z test?

I read in several books as well as in different posts (e.g. here) that independence is required for two-sample proportions z tests. But so far I could not find an explanation why this is the case and ...
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Two-proportion z test: is it best for my problem, and can I pool data from multiple “replicate” populations?

I am examining populations (cultures) of yeast cells and scoring them for a particular trait. The data is categorical; within a population, a yeast cell either has the trait or it does not. I wish ...
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55 views

Hypothesis testing for 2 proportions - for A/B testing

I was trying to understand the statistical tests to use during A/B testing and stumbled upon this documentation of the Amazon A/B testing SDK: ...
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141 views

Why is P value interpreted under null hypothesis? [duplicate]

P value is explained very nicely in the link . But still i have not understood Why is P value interpreted under null hypothesis?
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57 views

Which statistical test should I use to compare two samples?

I have two groups and must conduct hypothesis testing by using an appropriate stats test. Seeing as I have 26 participants in each group, do not have the standard deviation (or any other information ...
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33 views

What type of test should be used?

What kind of test would I use to find the answer to this? Is there evidence that cereals promoted in an in-store circular have a higher average number of units sold per store than cereals not ...
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52 views

Hypothesis testing - speeds before and after

I have the following data: ...
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390 views

two samples z test in Python [closed]

Does Scipy have a z test to compare the mean of two samples? I searched this page but couldn't find one.
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9 views

Accuracy Assessment: Do I still have to use any other test statistics?

I have a training set and a separate test set. In both sets, I have extracted two different parameters and I have compared the predicted values of these parameters to the actual values. So, I have ...
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91 views

two samples, hypothesis test of proportions t or z test

I have two samples of documents where one sample contains documents of a certain category and another sample contains documents of another category. I am analysing the occurrence of a certain word in ...
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45 views

Hypothesis testing with multiple variables

I'm trying to understand the process behind testing both A/B site changes for statistically significant increases in conversion rate, and also how then to expand this to testing multiple variables. ...
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28 views

Z test could be a good choice ? and z-test for multiple samples?

I've two samples with mean value $\mu $ and standard deviation $\sigma$ (normal distribution). Can I use a Z-test to compare them ? Also if I don't know the sample size ? If I've five samples to ...
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85 views

Permutation for large sample sizes (and z-test)

I was trying to do a permutation test on a large amount of temperature observations in R. Approximately 1700 temperature observations (g1) from one place and 2 ...
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38 views

Formulating a Z-test (or any other suitable test ) for survey data

I have a particular survey data related to a particular job. Out of a population of 90 people in this job, 36 people are in the lowest income group. 19 out of 36 people want to quit that job. I want ...
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39 views

Difference test for beta–binomial variables

Let $X \sim \textrm{Beta–Binomial}(\alpha_1, \beta_1, n)$ and $Y \sim \textrm{Beta–Binomial}(\alpha_2, \beta_2, n)$ and write $\mu_1 = \frac{\alpha_1}{\alpha_1 + \beta_1}$, $\phi_1 = \alpha_1 ...
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32 views

How do we perform a two-tailed z-test when we *do* know the population mean of the intervention sample?

I am in the process of working through the Udacity course Intro to Inferential Statistics. In Lesson 9: Hypothesis Testing, the following example is given. Say that we record survey data from all ...
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992 views

chi square test or Z test?

SO I have an outcome from a biological experiment, where I have counted the number of dead cells upon a mutation. For example, in once case - out of 120 cells we saw 16% of the dead cells, but our ...
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1answer
359 views

Are pupils in a school independent and identically distributed when compared to a national population?

I am interested in the way in which data are analysed in education. In England, pupils' reported test results are compared to national test results using z-tests. These results are then used to judge ...
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40 views

Obtaining Cohen's d from z-test statistic

After an ANOVA, I run post-hoc tests with the glht function in the multcomp package. glht ...
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201 views

Large overlap between confidence intervals, although z test for difference was significant

I have calculated a z test to examine the difference between two proportions. I found differences to be significant. The formula I used was: $$z = (p_1-p_2)/SE$$ where $$SE = \sqrt{ p ( 1 - p ) ( ...
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185 views

Power calculation of study using 2 sample z-test

This is not homework! I have two very different answers for a power calculation I have done on the below data - ...
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115 views

Difference between “common index” and “no common index”

I have been looking at the G*Power tool for Statistical Power Analysis but I am confused by the difference between two of the z-test options. ...
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494 views

Why use a z test rather than a t test with proportional data?

When testing the difference between 2 proportions why do we use a z-test rather than a t-test? Further, is there a simple way to conduct an omnibus test for significant differences between more ...
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148 views

Comparing sample proportion to population proportion

I have a data set consisting of a number of different hospitals. I am trying to compare the proportion for hospital X to the overall proportion in the data set (which includes hospital X). Should ...
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122 views

Alternative to Chow test for equality of estimates, when the data for the 1st group is not available

My goal is to compare published regression weights estimated from a sample in another country, with those of the same model established on our data.There is ample evidence on the web that a Chow test ...
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188 views

Xlstat and Pearson correlation coefficient: how are p-values calculated?

Someone asked me questions about his outcomes from Xlstat. Since I do not know this software at all, here is the question: How are p-values for Pearson correlation coefficients calculated ($H_1: \rho ...
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1answer
85 views

How can you derive the sample size to obtain a particular type II error rate?

I often see that the sample size for a $z$-test to achieve a particular type II error rate $\beta$ (at a given significance level, $\alpha$) is: $$n = ...
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756 views

Choosing between $z$-test and $t$-test

Background: I'm giving a presentation to colleagues at work on hypothesis testing, and understand most of it fine but there's one aspect that I'm tying myself up in knots trying to understand as well ...
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670 views

Interpretation of p-value in comparing proportions between two small groups in R

I wish to compare proportions between two small groups. In group 1, 2 of 18 students received honours. In group 2, 9 of 21 received honours. This is a small sample, so if I use the t-test: ...
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235 views

Simultaneous Z-test for the equality of two proportions (binomial distribution)

Is there a simultaneous test for the equality of two proportions when $k$ binomial properties are being tested? Example: Two groups of large size $n_1$ and $n_2$ are asked if they agree or disagree ...
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1answer
2k views

Likelihood Ratio Test and Wald test provide different conclusion for glm in R

I'm reproducing an example from Generalized, Linear, and Mixed Models. My MWE is below: ...
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74 views

Can I use a z-test on heteroscedastic data?

Suppose I have two methods that I test over time on the same data. I suspect that the methods degrade over time, and that this degradation is more or less linear. I want to know if one method degrades ...
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59 views

Standard error of proportion

In the first example of http://statisticshelp.com/confidence-interval Standard error of proportion is $$\frac{\sqrt {p(1-p)}}{n}$$ Why ?
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175 views

z-test vs t-test under assumptions

A traditional t-test to compare two means assumes independent random variables, $X_1,...,X_n \sim n(\mu_1,\sigma_1 ^2)$ and $Y_1, ...,Y_m \sim n(\mu_2,\sigma_2 ^2)$. One usually assumes normal ...
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171 views

What is the probability of success when two independent predictors co-occur?

Let's say I have a collection of objects. Each object has a set of predictive attributes where the attribute may be true or false. Each attribute when true predicts "success" with a known ...
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67 views

Two different methods…different results?

I have a response variable and 10 predictor variables (all ordinal). I wanted to see if there was any evidence of a relationship between the response and predictors. I used a two proportion z-test to ...
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27 views

Using a general linear model to perform z-test

I am trying to perform a z-test with a brain-imaging software. I was told that the best way was to use a general linear model with one subject in one group and the rest in the other group. Using this ...
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104 views

Can I use a two proportion z-test?

I have a response, "Satisfaction" that goes on a scale from 0-10 (where 0=dissatisfied and 10= very satisfied), and I have a predictor variable that also uses the same scale. I recoded the response so ...
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102 views

Most appropriate tests for online advertising significance data

We are running ads and want to construct two Excel formulas, one calculating the p-value for every other ad vs the one with the highest CTR (click through rate) and another that compares the CPA to ...
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340 views

Appropriate use of z test comparing two proportions

(Apologies for the cross-posting from math.stackexchange.com; I wasn't aware of this site until just now). I would like to test the performance of two algorithms. The second is a variant of the ...
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96 views

Testing whether two groups formed from a continuous variable differ on a binary outcome

18 people, who have been divided into 2 groups based on the semiquantitative expression of a protein (low vs high). Group 1 (low protein levels) has 6 people, Group 2 (high protein levels) has 12 ...