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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27 views

two sample z test in r

I am dealing with a dataset like this below ...
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When can we use a z-test instead of a binomial test?

I read from https://www.spss-tutorials.com/binomial-test/ and noticed that "So when can we use a z-test instead of a binomial test? A rule of thumb is that P0*n and (1 - P0)*n must both be > 5, ...
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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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25 views

Null hypothesis or alternative hypothesis

Actually I'm a bit confused how to choose my NULL hypothesis and how to choose the alternative one. suppose I have a sample of salary with mean 112,000 and I want to check if the population has mean ...
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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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1answer
55 views

Most appropriate test for A/B testing results

I looked answers for this question but couldn't find anything clear, everyone says something different. I wonder what is the most appropriate method for testing the statistical significance of our A/...
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Are there any problems with using an average of percentages for a 2 proportion z-test?

Let's say I have a 2 groups of test scores (ranging from 0% to 100%), and I wanted to compare their means to see if there was anything significant. I know I can average the test scores to obtain a ...
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16 views

How do I calculate sample sizes for multiple proportions, while maintaining a certain ratio of the sample sizes?

I am trying to perform z-tests for multiple proportions, while maintaining a certain ratio of the samples. For example, let's say I'm trying to compare 3 populations, and I want to maintain the ...
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13 views

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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36 views

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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14 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 ...
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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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What test to use to compare two proportions (and calculate effect size and confidence interval)?

There are many related questions here and elsewhere, but I found no satisfying answer. There are plenty of related tests and concepts: Z-test, chi-squared test, G-test, McNemar's test, Fisher's exact,...
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why can you perform t-test with the critical values of normal distribution? [duplicate]

I have estimated parameters and I want to check if they are significantly different from zero by using t-test. But since I have a large sample, I know I can compare the values with the critical values ...
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When to use Chi-squared and when Z test for categorical variables?

The problem is: There was a survey conducted among 1137 adults from California, Nevada, and Oregon. They were chosen randomly and they answered to the following question “Do you think Marijuana ...
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1answer
39 views

If sample standard deviation is biased, why do we use it in typical mean tests? [duplicate]

If sample standard deviation is biased, why do we use it in typical mean tests? Why do we not use an unbiased estimator by dividing the sample standard deviation by C4?
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47 views

One sample T test or Z test?

Given is an internet provider stated that the expected speed is at least 90 Mbit/s and the standard deviation is at most 5 Mbit/s. How there is a sample given with a sample mean of 88.36 and sample ...
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How to identify the difference in significance of two different z test for two proportion test?

I have two cell types (A and B) in a tissue. I have 5 replicates of RNA sequencing data in control and treatment condition for cell type and B separately. We are interested in identifying genes which ...
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1answer
40 views

one sample z-test standard error

Let's say I make the claim that 9 out of 10 dentists recommend a tooth paste. Next, I can ask 1000 dentists, and let's say that I find 700 / 1000 acually recommend it. so here $p_o = 0.9$, and $p = ...
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1answer
52 views

Required sample size to reach adequate power of a test

We got two types of treatment (type 1 and type 2). In our opinion, type 2 treatment has a higher performance and we would like to show this with research. We assume that type 1 treatment has a maximum ...
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28 views

Comparing multiple models across multiple groups or populations

Say I have a series of different regression models (e.g. 8 different models) which I conduct using data collected at a series of multiple locations (same predictor same response variables) and I have ...
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1answer
301 views

Proportion Test: Z-test vs bootstrap / simulation - different results

I'm learning hypothesis testing, and going through the following example: The CEO of a large electric utility claims that 80 percent of his 1,000,000 customers are very satisfied with the service ...
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1answer
30 views

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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1answer
44 views

Assumptions on the variance of the null model in one-sample Z-test?

Apologies if the answer to this is obvious, but I can't understand why the usual interpretation of the p-value (probability under the null model of obtaining a test statistic at least as unlikely as ...
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35 views

Z-test for comparing two estimator values?

My supervisor asked me to compare values of Pohar Perme estimator of net survival in two regions of the country using Z-test. Am I right that we cannot use Z-test for comparing these estimator values? ...
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1answer
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Help with calculating number of animals for a fetal surgery experiment

Rather odd question. I'm a surgical resident who is currently a research fellow in a lab studying fetal surgery. Our plan is to test a glue which we believe will help seal a uterus after we open it to ...
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1answer
75 views

siginificance testing of cosine similarity between word pairs from word embedding

I want to perform a significance test between two pairs of word embedding generated using Skip-gram model, as to how significant their cosine score is from mean similarity score. In order to do that I ...
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21 views

Accounting for factors that could be driving a difference between two means

just restarted data analysis so I've lost my edge quite a bit. Anyway, I've come across a problem and Im a bit stumped. I have a dataset for adverts. I want to measure the uplift in conversion ...
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1answer
69 views

Where is my potential flaw in my Z-test of Proportions?

I was working through this z-test of proportions example I found online. The online example solutions says that the difference between the groups is statistically significant, whereas I concluded it ...
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Why don't we need to use a t-distribution for difference of proportions tests? [duplicate]

In difference of proportions tests we use a Z-distribution. And in Chi square tests which I understand are in practice the same test use the square of the Z-distribution, the Chi square distribution ...
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Statistics to show the differences in population of the sample and city and by sex

Hoping for some help. I am trying to run some statistics for demographics from the results of a survey. I have male/female percentages as a result of the survey (45.1/54.9) compared to male/female ...
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4answers
74 views

In a card game, how to check if hand patterns are fair?

I'm playing contract bridge and the boards are dealt by a machine. Last time, one of the player suggested the boards are not dealt at random and I want to check that. At contract bridge, each player ...
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Can I statistically describe a single case/outlier vs. a distribution?

I have a dataset consisting of body weight and corresponding age for a bunch of healthy subjects (grey triangles below). I fit a nonlinear function to this data and graphed a 95% prediction interval. ...
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1answer
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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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1answer
117 views

2 sample Z test for non normally distributed data

I'm trying to analyse the impact of a marketing campaign and I'm looking to identify the most appropriate statistical test. I have one group of customers who received the campaign (approx 100,000 ...
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1answer
35 views

One-Sample Test for differences between questionnaire-answers

For a rather large sample (>800 participants) I have answers from a questionnaire, containing multiple Yes/No-Questions. What I want to find out is, if the proportions of yes & no's differ ...
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3answers
57 views

Standard normal intuitive understanding

What does it mean for a standard normal to have mean 0 and standard deviation 1? I'm having trouble understanding - what is a "normal variable"?
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1answer
32 views

Normality assumption for t/z tests

I have what is probably a silly question regarding normality assumptions for t/Z tests. As I understand, t/z tests require that sample data was obtained from populations following a normal ...
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1answer
54 views

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 ...
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1answer
38 views

P-value and confidence interval in MVT testing

Context: website A/B testing When calculating P-value and confidence intervals for each variation in an experiment with more than 2 variations (control, variation 1, variation 2 ...) should there be ...
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1answer
105 views

chi2 + z-test not yielding the same results?

With a 2x2 contingency table, I believe a chi2 test should be equivalent to a z-test -- from Wikipedia: "Two-by-two contingency tables: When the test is applied to a contingency table containing two ...
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1answer
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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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1answer
41 views

Help regarding calculating z statistic and p value

I am trying to solve a problem but couldn't see any way around it. So far, here is the progress $\mu_{pop} = 10 $ $\sigma_{pop} = \sqrt12$ $\mu_{sample} = 12$ $z = (\mu_{sample} - \mu_{pop})/(\...
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1answer
36 views

One-Sample z-Test

this is a really simple problem but I'm still in doubt about the solution. There's a population of workers and the goal is to see whether the rate of illegal workers has dropped to 20%. I have a ...
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2answers
312 views

Why does it says data should be normally distributed for analysis, when different test follow its own distribution (i.e. t, Z, F)?

Why does it say data should be normally distributed for statistical analysis when different test follow its own distribution (i.e. t, Z, F)? What does normality have to do with this?
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z test for sum of two percentages as greater than 100

I have a data set in which participants made a choice between two options--option A and option B. Participants were assigned to either choose an option or reject an option (so, there are two ...
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102 views

lower tail z-test

This is an exercise from Freedman, Pisani and Purves’ Statistics, 4th ed. (p. 552/8) An investigator has independent samples from box A and from box B. Her null hypothesis says that the two boxes ...
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Statistical significance of a difference between poll percentages with a small sample?

Analyzing my company’s internal survey results, I was stuck with calculating statistical difference between percentages. I usually used a Z-test as described below, but I am not sure whether it is ...
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32 views

Good resources for derivations of statistical significance tests

I am looking for a good resource to deep dive into mathematical derivations of statistical significance tests such as z-test one-sided two-sided t-test pair-wise t-test etc. I can find many ...
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63 views

How to do hypothesis testing for two different counts?

I have the following problem: in year A, we observe that a company sold N_A of its product, in year B, we observe that the company sold N_B of its products. How do I do hypothesis testing that the ...