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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Comparing z-values

If a test-statistics is expressed in z-values (instead of, for example, t-values), would it be appropriate to use those values for some further inferences? For example, to average a pair and another ...
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Significance of the difference between means

I am running an experiment on students in two of my classes. There is an online class vendor that promises higher test scores with only 2-3 hours more work per week. I decided to give one of my ...
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What hypothesis test should I use to compare the overall performance of two different athletes in a 100m race?

I am sourcing data from IAAF's website to test my hypothesis - Athlete A is a better athlete than Athlete B (comparing their times in the Olympics). Since I would be sourcing the data from IAAF's ...
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48 views

Can I use a Z test?

Can i use a Z test for 2 proportions for the following data? I have 2 samples - male (N=33) and female (N=51) Within the male sample no-one tested positive for a particular attribute. 33 Tested ...
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790 views

Which statistical test should I use (comparing two cohorts)?

So I am doing some research in the field of Medical Physics, in particular radiation treatment with photons and protons. Now, I have two cases I am unsure about. 1) Here I have several patients. ...
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76 views

Multiple planned comparisons of frequencies (based on a binary DV and multiple IV's)

I'm looking for the most appropriate way to to conduct multiple planned comparisons of frequencies. I conducted an experiment in which participants could come from one of two groups, 'Group A' and '...
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193 views

Comparing two vector of pecentages

Say, I have two vector of percentages (in this particular case, percentages represent a proportion of certain cell types in blood samples). Both vectors sum up to 1. For example, there are vectors ...
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556 views

Standard error of reconstructed slopes (coxph/coxme)

I have performed mixed effect Cox hazard regressions, and reconstructed the slopes to get group specific slopes (e.g. sex-specific responses to the explanatory variable). I aim to test whether the ...
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60 views

Testing variables in meta-analysis

I am conducting a meta-analysis of cognitive-behavioural interventions on self-esteem and I could use some assistance navigating through the statistical procedures. I have extracted pre-post scores ...
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270 views

Probability that two people get a certain number of heads on 100 coin tosses and all other outcomes with lower probability?

2 people flip a coin 100 times. The first person get 42 heads, the second person gets 58 heads. What is the probability of this outcome and all other possible outcomes that have an equal or lower ...
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85 views

Test of single proportion - how do i know population proprotion?

I have a study where I did a sample size calculation using N=2800, CI=95%, margin or error = 3.5% to yield n=613. In the study (auditing of charts), I wanted to look at the error rate in my sample. I ...
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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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719 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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844 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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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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26 views

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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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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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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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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I have calculated relative risk in SPSS with 95% CIs via a 2x2 table, but how do I then calculate the p value?

I have calculated relative risk in SPSS with 95% CIs via a 2x2 table, but how do I then calculate the p value? I thought I could use a two-tailed z test but can't seem to work it out
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Why does a two-sample proportion test with outcome Y and predictor X give the same result as one with outcome X and predictor Y?

I just noticed, while playing around in Stata, that this is the case, at least with three pairs of variables I tried out, which makes me think there must be some real relation there -- the z-statistic ...
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39 views

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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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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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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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? ...
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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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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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29 views

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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49 views

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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41 views

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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29 views

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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26 views

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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21 views

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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1answer
22 views

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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34 views

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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1answer
168 views

Use standard deviation of sample or population in z test

I am reading the book Statistics by Witte & Witte. Some questions puzzle me. Question 10.9: The normal range for a widely accepted measure of body size, the body mass index (BMI), ranges ...
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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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199 views

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 ...
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414 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 ...
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179 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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118 views

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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Null hypothesis test for proportions without minimum requirements? [duplicate]

I have a typical dataset: sample A (method A) which has 200 samples and 25 failures. sample B (method B) which has 240 samples and 0-10 failures. Note that 0 failures is possible. Null hypothesis is ...
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21 views

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 ...