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

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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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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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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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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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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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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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124 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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358 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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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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83 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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109 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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61 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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296 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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z-test in paper false? can Williams Hotelling test be used instead?

I am looking at the statistics of this paper: http://emotional.intelligence.uma.es/documentos/6-Extremera2011Emotional.pdf I am wondering how you can use the z-test to compare the two correlation ...
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51 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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63 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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101 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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67 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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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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448 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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146 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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590 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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71 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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How to validate % answering Yes/change exists is enough to say population is seeing a new pricing model?

I have a survey on pricing. There are questions where there is an A and B choice where the proportions are not independent (mutually exclusive group). Here I can use a binomial distribution in Excel ...
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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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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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Pooled vs Unpooled variance for AB Testing

I'm trying to A/B test two proportions and calculate the Z-score. My hypothesis is that the two groups are the same. Most of the formulae show the use of unpooled variance. Should pooled variance be ...
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156 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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59 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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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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77 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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79 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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234 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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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 ...
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Replace t-test with modified z-test - anyone ever seen this?

I just read about a procedure I'd never heard of, and was wondering if anyone has had any experience with it. In Donald Berry's "Statistics" book, he presents an alternative to doing a t-test by ...
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189 views

Testing for differences, would I use ANOVA?

I have four age groups all measuring different heights: How would I test for difference between the groups at 0.01 level of significance? Would I use ANOVA? Also - how could I establish which group ...
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235 views

is the z-test for difference of proportions valid for massive samples with tiny proportions?

Let's say I want to run a difference of proportions test where each side has n=23,000 but their proportions are 0.21% and 0.34%. ...
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532 views

Comparing change in average in two groups: Z-test?

I'm about to start up a project (as a high school teacher) that involves comparing the change in average between two different groups. It's an experiment, and the setup is the following: Obtain a ...
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608 views

Likelihood-ratio test or z-test?

Consider the following two logistic regression models: $$ \begin{aligned} &\text{Model A: }&P(Y=1)&=\frac{\text{exp}\left(b_1+b_2X_2\right)}{1+\text{exp}\left(b_1+b_2X_2\right)} \\ ...
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232 views

Appropriate test for comparing two sets of binary tests?

I have items made from two different materials. For each material I took a set of 250 samples and subjected them to a test which either broke them or did not. Which test could answer the question - ...
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97 views

Confusion related to significance test

I am trying to read the significance tests. However, I am a bit confused what exactly is the difference between chisquared test and z test. I read that chisquared is non parametric and it doesn't make ...
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634 views

Outlier detection for heavy-tailed data

Applying modified z-score for outlier elimination on some data (Iglewicz and Hoaglin, 1993), I discovered that a big proportion of the data (~10%) was outside the range ...
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261 views

Two-sample test of proportions

In my research, I aim to compare websites and need to identify if the websites differ significantly from each other. I have divided the website into two categories. I have sampled 45 websites in the ...
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Can I compute a confidence level for a z-test based on the size of the samples?

I'm doing a two sample z-test for the difference between means using pooled variance. Suppose I've run two experiments. In the first experiment, the sample size for the two populations is only 100, ...
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191 views

Is the power for a Kappa test the same as underlying z-test?

The Kappa ($\kappa$) test is a Z-test kind of test. If I am not very wrong, to compute the $\kappa$ test, we can just estimate the appropriate variance $\hat {var}(\hat\kappa)$ for the kappa statistic ...
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Why is the power for this test so low?

What follows is a theoretical power calculation for a practice exam, but this seems very low. Did I do something wrong? The problem and solution is as follows: In a drinks factory the mean fill of ...