# Questions tagged [z-test]

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.

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### Interpreting coeftest results; z-test; t-test, unfamiliar with the output

I am using coeftest to run z- and t- tests on a few different pieces of data. The output comes in this form: fit <- lm(dest_flood ~ type_flag, data = runsample) coeftest(fit) ...
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### McNemar test or Two proportion z-test?

Consider an experiment where a group of 200 people were asked before and after what is their preference, with possible outcomes being A and B. The research question is: Is there a difference between ...
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### Power analysis of group proportions when sample sizes cannot be guaranteed to be equal

I have a new UX feature, which I need to test out on users on a social media platform. When a user creates a post, he/she can add hashtags to gain community traction. As owners of the platform, we ...
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### Two Sample Independent Test for Proportions (z test or t test)

Context: I have two independent samples that I want to compare for equality through an AB test. The metric being evaluated is binary: user clicks or not (proportions). Question: I keep reading that z ...
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### Using a z-test for proportion in place of Chi-Square

Here's the study: Pam knows from prior research that children who are seated in a room with 4 doors are equally likely to pick any door when asked which door they would choose then leaving the room. ...
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### Hypothesis testing for ordinal proportions for multiple independent subjects divided between two groups

I have two biological groups - each with multiple subjects (7 in one and 10 in another). Each subject provides 40-80 observations, which can be classified into either of two ordinal categories. I have ...
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### Which statistical test to compare frequencies across groups?

I am running an analysis in which I want identify if there are significant differences in the features that make up two groups: people that commit crimes against children and people that commit crimes ...
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### A\B test and sample size calculate for time data

I am doing a statistical test (analysis) for the following case: As part of a product aimed at improving the quality and speed of code writing for developers, we have implemented a new feature that ...
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### Multiple Z-tests and independence

I'm currently working through this textbook question: "The length of three javelin throws is normally distributed, with: $$\mu = 253, \sigma = 8.4$$ What is the probability that the longest of ...
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### Z score from confidence level

I'm trying to find the Z score from a confidence level, for a Z test. I found posts with questions pretty close to this, but I'm still not sure of the general solution. These are the data I have: A ...
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### Calculating the SD for the z-test

The following picture, taken from some lecture notes, shows a very strange formula for calculating the SD, that I have never come accross. Can somebody explain how this formula yields the SD, even ...
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### When is the z-score/wald-score results will be a non-normal distribution?

If the hypothesis is valid the distribution of scores from several samples from the same population will follow a normal distribution for the z-test. That is true? I've made a simple experiment to see ...
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### Is the two sample z-test a Wald or Score test?

I saw the R prop.test returns the Chi square p-value, and it got me thinking this: Is the z-test with pooled standard error corresponding to score test, and the one with unpooled SE corresponding to ...
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### how to calculate sample-size of repeated time-serires measurements

I want to know if the nasal strips can really reduce my snoring or not, so I made a device to record and analyze my snores from 1AM to 7AM every night. This device gives me a "score" every 2 ...
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### Unclear which statistical test to use, t test or z test?

I have a scenario where I have an A/B test of a webpage. I'm trying to figure out using statistical analysis if more people spent time (in minutes, which is a float) on page B (the new page), than ...
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### 2 Treatments, comparison of proportions. Z test?

My design is the following: two treatments, T1 and T2. Population is divided in 4 age brackets, and the absolute numbers of enrolled subjects are: Age Treat1 Treat2 12-39 1387907 12196048 40-59 ...
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### Pass KS Test Fail Z Score Test

Im working with some messy data and was comparing two data sets. I used both the KS test and the Z-Score I found instances where Means would be found to be different under the Z score test but the ...
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### Test to compare 5 subgroups with population parameter

I have 5 subgroups , A,B,C,D,E each have their own mean and standard deviation. ...
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### Question about z-tests comparing two proportions

i saw a question online and i am confused with its answer. I will be grateful if anyone can explain the theory clearly to me. Question: In a monthly survey, last month got 55% approval from 1000 ppl ...
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### OLS uses t-test but GLM uses z-test in statsmodels python

statsmodels library in python offers two different approaches for regression, ols and glm. While they are different methods, if the error is normally distributed, they should provide the exact same ...
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### Two-samples Z-test alternative for small samples (categorical data)

I am looking for alternatives to 2 samples Z-test (2 independent samples) for categorical variables. I have two datasets (same indicators measured in 2020 and 2021) I need to understand whether ...
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### Why is the z statistic of a binomial proportion test normally distributed?

Suppose there is single sample $X_1\dots X_n$ of binary variable $X\sim Bern(p_1)$ and the following hypothesis is being tested: $$H_0: p_1 = p$$ $$H_1: p_1 \not= p$$ Let us use z-statistic without ...
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### Comparing two means from the same respondents taken at the same time without confidence level

I have a question about comparing the means of two dimensions both relating to the concept reputation. Information about survey research I have conducted a survey that measured three dimensions ...
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### Logistic regression : incoherent coefficient values from z tests?

I am working on a customer purchase problem. I have 150 campaigns sent by email, that I denote C0, C1 ... ...
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### two proportion z test with large population

I want to test for differences between two proportions, specifically, a complete count of the number of events occurring within a population in year 1 vs that in year 2. I thought a two proportion z ...
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### Best statistical test for aggregated group rate vs individual rate?

I'm looking to test the difference between an aggregated group weight (weighted average) vs an individual group rate? For example: Let's say we have 4 companies: A - 35/60 = 58% B - 120 / 400 = 30% C -...
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### The one-sample t-Test/z-test and inference validity

The CLT tells us that as we collect the means of different samples, the sampling distribution resembles a normal distribution and this way we can infer with a CI on the sampling distribution, the ...
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### Two Sample Z-test with Non - normal distributions (A/B testing)

I am doing my first steps in statistics and your help will be much appreciated. Sorry for not providing any data, since this is just a made-up exercise that I could not quite find the answer for. Let'...
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### Confidence interval and p value from prop.test() in R contradict each other

I am running the following simple Z test for proportions in R: prop.test(x = c(10, 20), n = c(100, 500)) The results are as follows: ...
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### Determine which independent variables are relevant by examining probability distributions?

I am looking to simulate patient outcomes from a data set that contains patient data such as age, diagnosis, some clinical variables, survival time after treatment and so on. My plan was to use a ...
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### How do you test for significance different in A/B Testing?

I just started learning about A/B testing and I apologize if my questions may be weird. After reading/watching some content with regards to A/B testing, I cannot fully understand on how to evaluate (...
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### Testing a linear combination of coefficients: t-test or z-test?

I am running a Seemingly-Unrelated-Regression (SUR) for 80 banks using Stata’s -sureg- command. local subsetvar HSBC-UBS ...
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### Comparing percentages of incorrect answers - is a t-test appropriate?

In my study, I asked participants to recognize an emotion (they were listening to an audio recording). Only one answer was correct, but the response scale included seven options. I calculated total ...
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### Hypothesis testing for two-samples

I have some questions regarding the process of choosing the appropriate statistical test. While I was working in my previous company, we were using T-test, Welch or Mann-Whitney for checking the ...
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### How to compare conversion rates from AB test when users visit multiple times [duplicate]

I've been asked to compute the minimum sample size for an AB test that my company is conducting for a tweaked recommender system. We will choose two groups of users, one of which sees only the A ...
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### Hypothesis Testing and Z-test for happiness at work

I'm doing a school project and decided to look closer into this COVID-19 thing that is obviously going on at the moment. I have a hypothesis that people in teams (at work) are happier at work after ...
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### Two Proportions Z-Test Accounting for Sample Standard Error

I have been using this equation for the two proportions z-test. However, what if each population sample from which proportions were derived has a different or considerable degree of sample standard ...
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### Statistical Significance of survey

I recently conducted a survey comparing the generated responses of 2 chatbots. Each participant was asked to complete two tasks: Select a generated response as "best" between 2 generated ...
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### One-sample z-test (?) and multiple comparison correction

I have a basic stats question. So I am comparing a patient with a condition to the population of healthy. Due to only have 1 observation/patient, I am looking into the z-score, i.e. calculating that ...
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### Having a problem getting the Intuition behind t-tests and z-tests

Say we have a population of $n$ rodents and that the mean of the population is $\mu$ with standard deviation $\sigma$, the standard error of means in this population would be $\frac{\sigma}{\sqrt n}$ ....
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### paired two sample hypothesis test on ratios in R

I want to conduct a paired test on two populations with ratio metrics in R. I'm really puzzled when I do a search in the web. Some tutorials suggest t-test or z-test and I am complete lost. I had the ...
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### Both Z-test and chi-squared apply in testing if a pill makes any difference in avoiding the flu?

I want to test if a certain pill would make any difference in avoiding the flu. I give the pill to group A and a placebo to group B. Then I count how many individuals got the flu in each group, and ...
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### Propotion test vs T-test

Proportion test - Helps to identify if there is significant difference in proportion across the samples.(i.e. the values are in proportion and denominator is in sample size of entire proportion) ...
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### AB-Testing on Website: Binomial Test vs Chi2 or Z-Test

I have data from a AB-Test on a website: Version A Version B #Visitors 10010 9912 #Conversion 320 275 I want to test the null hypothesis that the difference in conversion is due to chance. While ...
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### Which statistical test is correct to compare two groups of very different sizes?

I have two groups that consist of the tree fraction and elevation. The sizes of the groups are very different, and the mean of tree fraction and elevation are included in the table, below. They are ...
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### Fisher's Exact Test for many 2x2 data sets

I'm trying to find an appropriate test or method to determine if the presence of a binary condition causes a separate binary result, given lots of situations (data points) of the 2x2 input/output ...
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### t-test or z-test: assume normality or s≈σ?

Let's say I have a large sample ($n>30$) with mean $\bar{X}$ and standard deviation $S$. I can calculate only: $T=\frac{\bar{X}-\mu}{S/\sqrt{n}}$. If I want to use t-test for a hypothesis, then I ...
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### Is Z-test appropriate for A/B testing conversion rates for low proportions and high sample sizes?

We're using Z-test of proportions to calculate the significance of the difference in conversion rates between two variants of the same website. While it works as expected most of the time, we recently ...
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