Tagged Questions

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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Not able to understand the intuition behind $z$-test, $t$-test

I am not able to understand and appreciate the basic intuition behind need of this whole hypothesis testing framework, different kinds of tests, looking up tables, significance level etc etc. Why can'...
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Z-Test and T-test in SPSS custom table - Include 'Total' in comparision

I would like to not only compare columns' proportions and/or means but also each column's proportion and mean against the whole sample (i.e., the 'Total' column). Any way we can obtain that with SPSS ...
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Derive z- or t-statistic from p-values of regression coefficients from a probit/logit model

I have the results from an empirical study reporting the results for a probit and logit model. They just report the p-values of the regression coefficients. I want to derive the corresponding $t$-/$z$-...
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Why would one ever use z-score over a t-score?

Forgive me if this seems like an elementary question, but no amount of googling has turned up a satisfying answer for me. From what I understand, a t-score should be used instead of a z-score when the ...
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Statistical test for one sample proportions

I am carrying out a study into the handedness of racehorses. There are clockwise and anti-clockwise racecourses. I want to test to see if 1) horses are more likely to win if they are left handed on ...
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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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p-values in sign test

If we are given a list of $n$ independent measurments $\{0,0,1,0,1, \dots, 0,1,1,0,1\}$ of binomially distributed random variable $X$, we can use the sign test to check, whether the difference between ...
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Implicit assumption in z-test of difference in proportions?

In reading through the literature on z-tests for difference in proportions, I often see it stated that the null hypothesis only tests whether p1 = p2, not whether p1 = p2 = any specific value for the ...
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How can we ever know the population variance?

In hypothesis testing, a common question is what is the population variance? My question is how can we ever know the population variance? If we knew the entire distribution, we might as well know the ...
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How to measure extraneous and confounding variables?

The test-re/post/test methodology entails establishing a baseline, introducing a condition and measuring the effect size. The condition is known. But whether or not it yielded some changes, is what ...
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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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How to test if a sample proportion matches a population proportion, should I use the z-test or the t-test?

For (a), $H_0 = 0.75$ and $H_a \ne 0.75$. For (b), how can I get an answer with a $z$-value? Why can't I use a $t$-value to answer this question? Is the idea: $p \pm Z (p(1-p)/N)^{0.5}$?
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How do I test difference in Percentages?

I have some survey data and know the number and percentage of "yes" responses. How do I determine if any of the percentage yes regional responses are statistically different from the national yes ...
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Should we apply z-test or t-test for testing the difference between two sample means?

Below is a sample question from Wayne Daniel's Biostatistics 9th ed. This is a question under the subchapter - "Sampling from normally distributed populations where population variances are known". ...
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Z-test question: why variance between population and sample assumed as equal?

Example from wiki: Suppose that in a particular geographic region, the mean and standard deviation of scores on a reading test are 100 points, and 12 points, respectively. Our interest is in ...
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Comparing binomial outcomes from prediction algorithms in R

I've written a simple model to predict the outcome of soccer games based on some input. The outcome is either "H","D",or "A", short for home team, away team, or draw. I'm comparing the results of this ...
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Independent samples t-test: Do data really need to be normally distributed for large sample sizes?

Let's say I want to test if two independent samples have different means. I know the underlying distribution is not normal. If I understand correctly, my test statistic is the mean, and for large ...
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Chi post-hoc OR Z cell comparisons: do 2 proportion z-tests indicate most significant factors?

Attached is an example of some data I'm working with. I'm testing the occurrence of a rare behavior, while controlling for both education and the "bin" variable. The observed sample size is 129. This ...
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Appropriate Correction for 2 proportion test? --with example--

Below is an example of frequency data between observed and expected proportions. Can I simply run a 2-Proportion z test here? Or, would I be violating assumptions? If I were to run dozens of z tests (...
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Compare two population means at different time point

I am trying to determine the change in the size of a population during a 20 year period using two scenarios. I run the model for each scenario 100 times under different random seeds and then take the ...
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Probability of significant result in a second sample given first was significant

It's an example mentioned in Amos Tversky and Daniel Kahneman's Belief in the Law of Small Numbers: Suppose you have run an experiment on 20 subjects, and have obtained a significant result which ...
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Can someone explain what 'comparative error rate' is?

I have a set of rates of conversion for two different groups of ads. The rates are calculated by dividing conversion/impression (or, more simply, purchased/seen ad). I did a t-test for the ...
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Contradiction between confidence intervals and Z-test

I've got the problem with Z-test and confidence intervals. Z-test rejects null hypothesis (proportions are equal), but confidence intervals are intersect. Let us consider 2 companies. The proportion ...
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Can I do a z-test if population standard deviation is unknown?

Edited: Suppose I'm trying to compare a sample of 45 articles drawn from a population of 5,000 to see if there's a significant difference between the sample and population means. The population ...
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Chi square test vs z test

I have got results for a survey and was wondering which test I should use to show there is a significant difference in my results. It is a survey on apple charger breakages and other phone charger ...
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Proportion test with null hypothesis p1=x*p2

I'd like to compare the proportion of two sets of binomial data where the null hypothesis is not p1=p2, or p1-p2=x, but $$H0: p1=x*p2$$ I've been computing a z test as ...