# 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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### 2 sample z-test scores larger than 12 for hypothesis testing. Is it correct?

I am using a dataset and taking input dataframe df. I am doing a hypothesis testing that for all features male and female mean are same. I am doing 2 sample z statistic. I am doing the following: ...
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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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### Check if a subset is significantly different from the dataset

I have a dataset with violence rate per City that can be grouped by State. I need to check if any State has significantly different violence rates than the entire dataset. How could I achieve that? ...
148 views

### 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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### Different z and Wald values in logistic regression analyses between SPSS and R

I am running a binomial logistic regression in R. My colleague is running the same regression in SPSS. Our DV is dichotomous and data is non-normally distributed. The IVs are a mix of categorical and ...
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### Intepretation of a sample size convergence assumption in a 2 sample Z test

Let us consider a two sample problem modeled with a fixed sample sizes $n_1, n_2$ (i.g without assuming that the group is chosen randomly). If we want to proof asymptotic normality of a classic Z-...
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### A realistic example of a one sample mean test for a hypothesized population mean

One sample mean tests are used to test whether the sample mean is statistically different from a known or hypothesized population mean. Real life examples given for the latter type (hypothesized ...
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### Testing difference in mean with very large discrete sample set

I am evaluating whether two thermometers are equivalent using a difference-in-mean hypothesis test. Both thermometers registered the daily maximum temperature over a few years, accurate to 1 decimal ...
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### T-test for marketing data in excel

I am currently running an A/B test, and I’m not sure how I should be arranging my data to run a t-test in excel. I have 1 control and 2 variations that I am running for an advertising campaign - the ...
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### Unsure how to approach evaluating statistical significance for two very different sized samples

Some basic overview: Problem Statement: Comparing average transactions per user between two groups Group 1 Size: 6.5M Group 2 Size: 500K Now, it's been a month and we've seen about of unique users ...
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### Does a z-test make sense here?

I have been assigned to collect data about the contents of an additive in wine. The additive is approved, but also fairly poisonous in the right amounts. The dataset consists of test results for +3000 ...
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### What is the alternative for one sample z test?

I have a sample of 350 and I have to compare the anxiety score among different variables. I wanted to apply the z test to compare the means but my data is not normally distributed. Is there an ...
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### z-test for proportions where successes are less than 10

I have this data; ...
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### What would be the right statistical test and why am I getting different results using Z-test and confidence intervals?

I am trying to determine whether the observed differences in the proportions for two samples are significantly different. 0-hypothesis: The proportions are the same for both samples Alternative ...
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### What would be the right statistical test here?

I want to know whether the proportions for two samples are the same. 0-hypothesis: The proportions are the same for both samples Alternative hypothesis: The proportions are different. I know the ...
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### a method to perform statistical test to test the diff of mean is larger than a threshold

I'm trying to test the difference of means of two groups, A and B, is larger than a specific value or not. The two groups are considered as sampled from two binomial distributions and can be ...
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### Equivalence testing: Is it appropriate to set the equivalence bound such that I can reject H0 at alpha=0.05?

I have conducted a survey. One sample answered a binary question (answer A or B), once with and once without treatment. Now there does not seem to be a treatment effect as the proportions of answers ...
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### Difficulty understanding the intuition behind two-population z-test

I'm trying to understand how I would compare conversion rate data in an A/B test. I've read a lot of posts on this, all of which generally boil down to computing a z-score using something like  z=\...
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### How to compute p-values from modified z-scores (Iglewicz & Hoaglin) for FDR correction?

I have made good experience with using the modified Z-score for outlier detection in approximately normally distributed data, which was also discussed e.g. here and here. However, if applying many ...
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### t-test for means of daily conversion

Let's say I'm a/b testing a new site version and want to know if it improves conversion. I realize that conversion is a proportion so I would use a Z-test for this. But then I am thinking - it is ...
403 views

### z-test in statsmodel with known variance/std

To my knowledge: If I have a small Gaussian distributed data set and I know the true variance $\sigma$ of the data then the z-test is only appropriate if the standard deviation of the estimator is set ...
177 views

### Comparing proportions of 3 groups using chi square and z-test

I was wondering if my plan for analyzing my data was appropriate: I am trying to compare proportions between samples from 3 populations (N= 53, 54, and 56). I ran a chi squared test and found a ...
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### two sample z test in r

I am dealing with a dataset like this below ...
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### Calculation of critical values

Are the critical values for the two-sample t-test with unequal variances calculated the same as for the two-sample z-test?
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### I'm comparing multiple demographics across multiple samples, Chi-square test or 2 sample t-test

I would like to compare the demographics of people my company serves with the demographics contained in a subset of the American Community Survey 2017 data. The first set (n=35751) of data is a person-...
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### Statistical comparison of 3 relative survival values

I have to compare relative survival (have 5-year estimates with SEs and patients number per group) across 3 time periods. Cannot use log-rank etc as (probably) it is impossible to operate with raw ...
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### What A/B test calculator can I use to calculate the minimum same size for uneven split between control and treatment groups?

I have only come across A/B test calculators that give the minimum sample size per variation for 50-50 split between control and treatment. I am running an A/B test for conversion rates with a 80/20 ...
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### Mean Sickness Absence at different company sites statically significant ? T-Test, Z-Test?

I'm relatively new to stats so apologies if this is rather trivial but I cannot find an answer (I work in the workforce information dept of a largish company). We have 10 sites, and I calculate the %...
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### Find if two groups are different where one is a subset of the other

I have a dataset of 3,500,000 categorical observations that can be grouped by an ID. In these categories u occurs 25,000 times. How can I test to determine if a ...