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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50 views

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? ...
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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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50 views

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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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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29 views

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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2answers
65 views

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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1answer
18 views

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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16 views

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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197 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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56 views

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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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 ...
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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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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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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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333 views

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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420 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
62 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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36 views

Simple question about difference of two proportions testing

It is usually explained in biostatistics textbooks that to do a z-test for the difference of two proportions, it is necessary that p*n and (1-p)*n are both equal to or above five for both samples. ...
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41 views

correct test for comparing proportions across groups

I have 2 overall groups A, B. In both A and B, I have 3 individuals, each scoring a certain percentage on a test. If I want to compare the scores across group A and B, is the correct process to sum ...
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237 views

What is the Appropriate Test to Compare Pearson's Correlation Coefficient?

Let say I have this simplified data set which contains four variables (2 categorical, and 2 numerical types): ...
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113 views

Reason for the appropriateness of the z-test for linear regression slope check

I know that the z-test can be used to compare the slopes of two regression lines (lines fitted to two separate data sets). What I do not understand is WHY we can use the z-test for that? Therefore I ...
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36 views

What is the method for solving an equation in which a data set is compared with a "standard" with a known mean and variance?

For my homework, I have been asked to solve the following question: Suppose Wal-Mart had to pave over a valuable wetland to make room for a new Super-Store and associated parking lot. In obtaining ...
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41 views

Should I be using Z-tests or T-Tests for my scientific data?

I've conducted a survey for my thesis where I ask a series of questions of the format: A statement relating to the experiment Then the participants answer ...
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244 views

algorithm for testing a variable

I want to test if a quantitative variable is different in 2 groups. As for what I understood so far, here is the algorithm I should use : if the length of my 2 subgroups are >30 --> z-test else, ...
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1k views

How do I interpret a negative Z-test (two tailed for 2 proportions)?

I used my calculator to do a two tailed Z test for two proportions. Here's the data I input: X1 is 834 n1 is 3610 X2 is 145 n2 is 495 I chose p1 not equal to ...
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131 views

What would be appropriate test to compare two lists of dichotomous variables?

Colleagues, can't wrap my mind on simple question, please help! I have two products and list of their attributes. My respondents make an answer which product on each attribute they prefer. Finally ...
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1answer
96 views

Comparing 2 sample proportions from independent populations

Consider a hypothetical situation, due to a new teaching method being implemented, I want to test whether there is a significant difference in the proportion of students that have passed a particular ...
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78 views

Can I use a two proportion z-test if large counts isn't met but the population is normal?

I know that if the number of successes and failures are all greater than 10, the sampling distribution would be approximately normal. However, if one of the failures are not equal to ten, but it is ...
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254 views

Formulate a z-test into a general linear model

I've heard it said that most statistical tests can be reformulated within the GLM framework. I can see how that can be done with a two-sample t-test (dummy code group membership and interpret the ...
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396 views

Confusion about z-test and chi square test on a very basic example

I am confused with the difference between z-test and chi square test. In book Agresti 2007 An introduction to categorical data analysis, page 9, the author had an example of testing Do a majority ...
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421 views

Is it correct to set a control mean to compare the Z-Scores of several sub groups too? And how do I do this?

I am trying to undertake some Z-Tests to see the level of effect in Standard Deviations of 8 separate treatments compared to a control mean. However there is one thing that has constantly confused ...
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147 views

2-Proportion Z-Test

I want to compare, with 2-proportion Z-Test, the number of student visits to school nurse office in Q1 of 2015 to Q2 of 2015. What do I use for sample size for Q1 and Q2 when it’s different each ...
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190 views

1 sample z test of proportions

We are trying to work out whether what we currently do is accurate. We want to work out if a proportion (% scoring 5 on a 5 point scale) are significantly below a target score. Normally a 1-sample z-...
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1answer
51 views

What type of test should be used?

What kind of test would I use to find the answer to this? Is there evidence that cereals promoted in an in-store circular have a higher average number of units sold per store than cereals not ...
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167 views

Hypothesis testing with multiple variables

I'm trying to understand the process behind testing both A/B site changes for statistically significant increases in conversion rate, and also how then to expand this to testing multiple variables. ...
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99 views

Z test could be a good choice ? and z-test for multiple samples?

I've two samples with mean value $\mu $ and standard deviation $\sigma$ (normal distribution). Can I use a Z-test to compare them ? Also if I don't know the sample size ? If I've five samples to ...
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803 views

Alternative to Chow test for equality of estimates, when the data for the 1st group is not available

My goal is to compare published regression weights estimated from a sample in another country, with those of the same model established on our data.There is ample evidence on the web that a Chow test ...