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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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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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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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38 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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37 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
39 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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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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130 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
32 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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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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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
34 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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19 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
52 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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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
55 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
31 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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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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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
30 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
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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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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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methodology to analyze differences between groups

My dataset (n=2,000) shows total daily sales and I can plot a trend and show via a s-test that the average number sales is different in 2016 vs 2017. I also have the information in the data indicating ...
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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
38 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
35 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
307 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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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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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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2answers
58 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 ...
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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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What is wrong with one tailed z-tests for a proportion?

After answering How to analyze observed vs expected when expected is just a proportion? by suggesting that the OP uses a one tail Z-test for their proportion data, I got into a debate in the comments ...
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501 views

Z-score computing for two sample proportion comparison

Assume I aggregated the following results: ...
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1answer
353 views

Determining samples sizes for an A/B test using z-test and chi-square test

Assumptions I consider an A/B test where there is a control group and a variant group. Each observation can either be true (converted) or false (not converted). I evenly and randomly split the ...
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301 views

Test difference of population proportion and weighted sample proportion

I want to test for differences of the known proportion of the population vs. the proportion of a sample. The sample is weighted by sampling weights. The sum of weights is equal to the size of the ...
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1answer
89 views

Hypothesis testing question — how to define the null hypothesis to draw a conclusion

Here is a hypothesis testing question I'm trying to work out but am struggling with how to draw a conclusion, maybe I'm not defining the null hypothesis correctly. The question is as follows: Test ...
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1answer
41 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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1answer
23 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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1answer
883 views

Sample mean Margin of Error and C.I [closed]

I have data on the mean assembly costs for the first n=36 days of production. It is assumed that the following data follows a Normal distribution: ...
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0answers
175 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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76 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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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 ...