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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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Comparison of proportions within one group but between two different questions: One-sample or two-sample z-test?

I have 300 participants who answered several questions in a questionnaire on a five-point Likert scale. I want to compare the proportion of the answers of either 1 or 2 with the proportion of the ...
Björn Stannerman's user avatar
2 votes
3 answers
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Hypothesis Testing for Means & Proportions. t-test vs z-test

How can I convince my teacher that he is wrong in this task? We were given the following task and my teacher says I have to use a z-test. In my opinion I have to use a t-test.The task is as follows: A ...
Apro9991's user avatar
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When testing significance between a regression coefficient of two data sets using a Z-test, how to interpret the z-value?

I am following the methods described in: Clogg, C. C., Petkova, E., & Haritou, A. (1995). Statistical methods for comparing regression coefficients between models. American Journal of Sociology, ...
jack kelly's user avatar
1 vote
1 answer
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How to perform a z-test for a 2d-gaussian?

I have N 2-dimensional points (X,Y) where X and Y are gaussian distributed and have a strong correlation, i.e., X and Y are not independent. What is the simplest way to perform a z-test? In other ...
Roshan Satapathy's user avatar
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Statitical comparison of regression prediction to sample of data

I have a dataset, let's call it data1(x,y), where the data y is measured at 16 values of x. I use this dataset to fit to a 3-parameter model. I can obtain estimates for the three model coefficents ...
Davide's user avatar
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1 answer
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Z-test with no relevant sample size as I have a Gaussian probability distribution

I have two Gaussian curves, there are not samples, these are just probability distributions essentially. So I can do a Gaussian fit on them, or also a weighted average and weighted variance on the ...
Dominik Duleba's user avatar
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What is the best statistical measurement for collocational analysis?

I am a beginner with statistics and corpus linguistics, so sorry in advance if my explanation have gaps in it. So I want to perform corpus linguistics collocational strength analysis on a given corpus,...
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Best stats test for a resume audit study evaluating bias

I am testing an applicant tracking system and giving it resumes that have implicit mention of race, and asking the system to rank them. There is a control resume with no implicit mention of race. For ...
Bobbi Lynn's user avatar
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Is a log transformation valid for a pre-experiment sample size calculation using 2-sided z test?

Goal I am conducting a pre-experiment analysis to determine what the necessary sample size is given a specific power, significance level, and lift. Data This is for a research question where I have a ...
rdos84's user avatar
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Why do Z-tests use standard error (using the know population standard deviation) and not only standard deviation?

I understand why a T-test uses the standard error, after all we are dealing with the inaccuracy of small samples. $$T = \frac{\bar{x} - \mu}{\bar{s} / \sqrt{n}} = \frac{\bar{x} - \mu}{SE} $$ But why ...
Daniel Gustavo's user avatar
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Should I use a $\chi$-squared test or a z-test?

I have a dataset with four groups $G_i$ with $i = 1, 2 , 3 , 4$, and in each group $G_i$, a certain number $n_i$ of observations are favorable. I want to check if there are any differences between the ...
Samuel's user avatar
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1 answer
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Can evidence of absence be obtained only in one-sided hypothesis tests?

It seems that if a one-sided Z-test returns a p-value $>1 - \alpha$, you have enough evidence of absence to reject the alternative hypothesis in favor of the null hypothesis, because if you were to ...
user10478's user avatar
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Z Test basic problem

The mean selling price of new homes in a town over a year was \$2,200,000. The population standard deviation is \$200,000 . A random sample of 81 new home sales from this city was taken. What is the ...
Slow Ninja's user avatar
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Z test for proportion of sums

I want to perform a Z-test for two variables: $ X $ (Buyer proportion) and $ Y $ (Spent proportion \$ ). Below the table you can see a dummy example of the data I have: Let's assume the conditions ...
william giraldo cuadros's user avatar
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Hypothesis testing on a model's inference

I have the following situation, which I've mapped to an example below. At the conclusion of an A/B test done on a website I've a metric I care about. Let's assume its the number of users clicking on a ...
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Why is the sample standard deviation used in the z-test?

The assumption of the z-test is that the population standard deviation $\sigma$ is known. With this in mind I tried to manually compute the p-value for a (one-tailed) z-test that the sample mean $\bar{...
monade's user avatar
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One proportion Z-test and Chi Square Goodness of Fit should be identical but return different results

My understanding is that a Chi Square Goodness of Fit test and a one-proportion Z-test should have identical p-values and be equivalent (https://youtu.be/-Vssir6yUNQ?si=4-t9Np9h4bedU9xN&t=423). ...
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On the success or failure of an experiment

Recently I've been asked this question and I wasn't really able to give a solid answer from a statistical standpoint. I hope someone can help me :) Statement Let's say that in a given region, in a ...
rusiano's user avatar
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2 proportion Z/T test?

I want to find out if 2 proportions are different or not. For one, sample size is <30. For the other, it's much >30. Can I use the Z test since one size is large? Or do i have to use the t test? ...
viktor nikiforov's user avatar
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Did I use z-test correctly in this problem?

The problem: It has been said that it is difficult to distinguish Coke and Pepsi by taste alone, without the visual cue of the bottle or can. In an experiment that I did in a class at Stanford, 10 ...
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2 answers
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Why are there two formulas for the z-test?

There are two formulas commonly used in the z-test: one involving the standard error (se) and the other involving the standard deviation (std) of the population. The formulas are as follows: ...
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At loss regarding a suitable hypothesis test for proportions in the same population

I'm dealing with a population where there are $5$ categories $A, B, C, D, E$ and I would like to make the claim that $A$ is the most common category in the population (i.e., the most frequent). I ...
Essam's user avatar
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Compare two proportions with a Bayesian analysis

I'm conducting an experiment in which participants receive either an object A or an object B. Next, we ask participants if they want to trade their objects with the alternative object (i.e., object B ...
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Comparing two proportions within contingency table for small sample size [duplicate]

I need some help for a statistical analysis. I have the following contingency table : I would like to compare p3 and p2, that is the comparing the proportion of event in G2 and the proportion of not-...
user381165's user avatar
1 vote
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40 views

Comparing groups based on data containing proportions without raw counts

I have 2 object types, A and B For type A, I observe delivery to demographic groups x1, x2, x3, x4.... xn. For type B, I observe delivery to the same demographic groups x1, x2, x3, x4.... xn. x1(a) + ...
user81371's user avatar
1 vote
0 answers
8 views

Compairing multiple distributions from repeated measures design to a refrence value

I have 24hrs of temperature measurements taken in one minute intervals for a set of individuals. Thus, there is a non-independent distribution of temperatures for each individual as each measurement ...
JKO's user avatar
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Can I use the Z-Test with estimators for mean and standard deviation?

I'm trying to select feature columns in a binary classification model. I'd like to remove near-constant columns that don't predict the target column values very well. One way of defining this is the ...
Connor's user avatar
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125 views

Are large samples always needed for a Z-Test?

I have read that you should use a Z-Test when you have a sample size $ n > 30$, because this is where your sample distribution becomes normally distributed. The Z-Test equation has more power when ...
Connor's user avatar
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Can you use a Z-Test with a sample size of 1?

Background I'm performing a feature selection process on a fraud dataset. The dataset is made up of roughly 300 columns and 40,000 rows. It has a single binary indicator for a target. A lot of the ...
Connor's user avatar
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Significance of a single point, or population of 1

This may sound simple but I'm lost. I have a simple experiment 15 controls and 15 treatments. 13 of the 15 controls were positive, but only one of the treatment samples was positive. This makes the SD ...
J Slowik's user avatar
2 votes
1 answer
1k views

Why is the confidence interval for difference in two proportions inconsistent with the p-value for this difference in R prop.test()?

I calculated the difference in 2 proportions using the prop.test() using some exemplary data I found in internet. ...
kmonk_gun's user avatar
2 votes
1 answer
195 views

Visualizing how the 2 sample Z test works

In my stats class, we are talking about the 2 proportion $Z$-test, which compares two sample proportions. The test statistic is given as: $$ Z = \frac{\hat{p_1}-\hat{p_2}}{\sqrt{\hat{p_c}(1-\hat{p_c})...
Max0815's user avatar
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Z test for paired proportions when only the two proportions are available

I am familiar with formulae for paired proportions Z test when the crosstabs table is available. However, if only the two proportions are available, I am having trouble to figure out what is the S.E. ...
JPMD's user avatar
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0 answers
42 views

Selecting an appropriate statistical test

I have two sets of data (>10k observations), each having a binary feature describing the activity of every customer within the groups (1=active, 0=inactive). I've seen parametric tests being used ...
simon's user avatar
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1 vote
1 answer
260 views

How to check normality of a binary data(True/False) for z proportion test?

One of the three conditions that should be checked before conducting two-sampled z-test for proportions is "check for normality"(link for the source: https://vitalflux.com/two-sample-z-test-...
user378299's user avatar
1 vote
1 answer
118 views

Z-Tests tests of Two Proportions for Continuous Data?

Why can't we do z-tests of two proportions for data from a continuous variable? For Example, if I have sample sales data (continuous, dollar) from a company and want to see if the proportion of sales ...
mich's user avatar
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2 votes
0 answers
104 views

Z-test with large sample sizes but small proportions

I'm running an A/B test to determine if a change/treatment we're proposing for our website has an impact on users opting into a specific (niche) category of notifications. To do so, I'm performing a ...
Theway's user avatar
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1 answer
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Can we use z-test when the population standard deviation is known but the sample size < 30?

Let's say I know the population standard deviation, but the sample size is small (≤30). Can I use the z-test? The reason I ask is that I see two different statements. We can use the z-test, if we ...
Fred Chang's user avatar
4 votes
4 answers
1k views

Is a t-test applicable here in comparing two proportions?

I have 3 categories of tissues examined by microscopy (A , B and C, 12 of each). I want to test whether the proportion of tissues staining by a particular dye, differs in the three categories. Each ...
smishra's user avatar
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15 votes
2 answers
2k views

Why is t-test more appropriate than z-test for non-normal data?

(Disclaimer: I am aware that some form of this question has been asked many times on this site, e.g. this, this and this - I was hoping to find a definitive answer to this from Google but I am still ...
dummy's user avatar
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1 answer
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A/B Testing Question - Power Analysis for Two Proportion Z Test

I'm having a hard time wrapping my head around experiment design and what appears to be a disconnect to experiment outcome analysis. If I am proposing a z test of two independent proportions (...
cjmsmcl's user avatar
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0 answers
58 views

For a continuous distribution, can I replace the mean by the median in two sample z-test?

For a continuous distribution, can I replace the mean by the median in two sample z-test? Assuming that populations are normally distributed. I feel like they can because both median and sample mean ...
Shuheng Zheng's user avatar
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1 answer
87 views

Contradictory results while performing Z-test

Hello Everyone, I'm relatively new to statistics and this community so please bear with me and forgive me if I commit any mistake while asking my question. For starters, here are two hypotheses tests ...
Tanay's user avatar
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1 vote
0 answers
134 views

Comparing two classifiers with two proportion ztest by using balanced accuracy

I'm looking for statistical differences between two classifiers by applying the two proportion z-test formula to them and then performing the hypothesis test. If p1 and p2 are the balanced accuracy ...
f_s's user avatar
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2 votes
2 answers
141 views

Why are ztest and chisquared test not returning equivalent sample size results?

I'm using the statistical software G*Power to find the minimum sample size needed to detect whether or not the difference in two proportions is statistically significant in an AB test I'm setting up. ...
Pedro Alonso's user avatar
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0 answers
36 views

What are the distribution values (mu, sigma) for alternative hypothesis of differences between two proportions? How to calculate?

When comparing two independent proportions (p2, p1) in an A/B test, null hypothesis states that the difference is 0, while the alternative hypothesis states it is something other than 0, let's say mu1....
kukushkin's user avatar
2 votes
2 answers
1k views

Minimum sample size calculations for two-sample two-tailed proportion z test

I'm struggling to reconcile some minimum sample size calculations. I'm seeking a minimum sample size for two-sample two-tailed proportion z test. I set my parameters as follow... alpha = 0.05 power = ...
Kees's user avatar
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1 vote
0 answers
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Finding statistical significance difference using Z score test using r

I wonder how to perform the z proportion test to check which COG category of Shewanella_sp_Alg231_23 is significantly high p (<0.05) from other genomes. To undersatnd I have attached a bar braph. <...
umar's user avatar
  • 111
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0 answers
102 views

Testing if the difference of the sum of two distributions is significative

I have two distributions and I wish to understand if the difference of the sum of the elements sampled from these distributions is significative or not. I have set the problem this way: I have $n_{x}$ ...
Max's user avatar
  • 1
2 votes
1 answer
852 views

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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