Questions tagged [z-statistic]

The statistic used in z-test, namely the ratio of a parameter estimate and its estimated standard error.

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Confidence Interval - small dataset (30 records)

I'm trying to calculate a confidence interval for data analyst salary population. I have a very small dataset from a job posting site that contains only 30 records. The dataset doesn't follow normal ...
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Calculate probability of minimum number of sample types within a sample distribution - z-statistics vs. binomial distribution

(The title may have to be changed, because I am learning statistics and can't describe problems through the use of the correct terminologies yet) I have the following question: "90% of all plant ...
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In standard normal distribution table how i deal with value of Z greater than or equal to 5

How can i deal with sample distribution table when Z is greater or equal to 5? For example:(-2.04 <z<-5.96) Sample distribution table value for -2.04 will be 0.2018 then what will be the sample ...
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Using random intercepts or z-standardizing within factors: Two identical ways to account for variance between factors?

I have the following (simple?) question about statistics: I have a dataset where I look for correlations between variables and would like to control for differences between factor levels. For ...
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Is this formula for percentile from z-score correct?

Preface: I am not a mathematician. I have a basic understanding of statistics but am not familiar with mathematical notation beyond high school algebra. I am a software developer maintaining medical ...
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critical Z-statistic vs sample Z-statistic

A hypothesis that the population mean is less or equal to $x$ should be rejected when the critical Z-statistic is greater than the sample Z-statistic. $x$ is any number. If $x=5$, the statement is ...
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Comparing n population proportions

In the examples I am reading (which includes Stats for Dummies!!) most examples of null hypothesis testing reference 2 populations. However lets say I complete a survey and get the following results: ...
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Should we always calculate the z in a confidence interval as 1 - (alpha/2)?

I'm currently beginning my studies in statistics and all of the examples of confidence interval questions I studied used (let's assume a 95% confidence interval) as a z formula ...
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This function can get p-value from which statistics?

I know that I can get p-value from z-statistic (called zval here) using following function (Python): pval = 2*(scipy.stats.norm.sf(abs(zval))) or with: ...
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Digital Product A/B Testing: Z vs T test

I'm a beginner in statistics. When it comes to digital product A/B testing, I'm told by my company's analyst that they typically use the T-test for the hypothesis testing Why would we not use the Z-...
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What does it mean if Z statistic is -Inf?

I have ran a Wilcoxon rank sum test to compare two independent samples. I now want to get a Z statistic to report, but when I do so, it results in -Inf. What does ...
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Eta-squared from Kruskal-Wallis in R

Is it possible to calculate Eta-squared from Kruskal-Wallis test results? I know how to do it by hand for the ANOVA or Mann-Whitney using the Z-statistics, but i must use the KW test for my current ...
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Why does the pivotal quantity $g(X,θ)$ have to be a monotonic function of $θ$ for a fixed $X$?

I'm learning about pivotal quantities, which are functions $g(X,θ)$ of the data $X$ and the parameter $θ$. One property they must satisfy is that $g(X,θ)$ is a monotonic function of $θ$ for a fixed $X$...
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Standard deviation Vs ٍٍStandard error

I'm little bit confused, when I want to standardize a normal distribution, when to use standard error and when to use standard deviation ?. In statistics we often use samples so, is it always we use ...
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Using the $Z$-test instead of the binomial test for small $n$ - effect on power and Type I error

Setup Let $M \sim \text{Bin}(p,n)$. Let us then state the following two hypotheses: $$\begin{align} H_0: p = 0.5 \text{ vs } H_1: p > 0.5 \end{align}$$ To test these hypotheses, I could use the ...
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Testing a null hypothesis using positive and negative z-score; accept or reject

Theorem:: To test null hypothesis $H_0$: $p_0$=$p_{1}$ versus alternate hypothesis $H_1$: $p_0 \ne p_{1}$ at the $\alpha$ level of significance, $H_0$ should be rejected if $z$ is either $(1)\le -z_{\...
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How to aggregate multiple Z-scores

Is there a way to aggregate multiple Z-scores to get a single Z-score that corresponds to the probability that no null hypotheses are rejected? Backstory: We have a tool that has some error E that ...
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Why do GLMs use z-scores for parameter inference?

Generalized Linear Models typically use z-scores for inference on parameters ($\beta$s) (see here, for example). This assumes that parameter estimates ($\hat{\beta}$s) follow a normal distribution? ...
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Why is $z$-value more meaningful than $p$-value for very low $p$-values?

In a comment to Jaap's answer to this question about reporting tiny p-values, amoeba says "Once the $p$-value is below 0.0001 or something ... it's probably more meaningful to look at $z$-value than ...
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How can I obtain z-values instead of t-values in linear mixed-effect model (lmer vs glmer)?

I am wondering why in my lmer model the summary() only yields t-values rather than z-values, such as here: ...
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Normally distributed estimated parameters in logistic regression

I was reading the book Introduction to Statistical learning, where in z statistic was used to for hypothesis testing for parameters, so my doubt is that as response variable is not normally ...
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Choice of null and alternative hypothesis

A firm producing tobacco cigarettes claims that it has discovered a new technique for curing tobacco leaves, that results in an average nicotine content of a cigarette of less than 1.5 mg. To test ...
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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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Likelihood of a given sample mean? (p-values versus confidence intervals)

My issue is with comparing p-values to confidence intervals. The different values being churned out are too great, and I don't understand why. So, an example to illustrate my problem: A sample of ...
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57 votes
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A/B tests: z-test vs t-test vs chi square vs fisher exact test

I'm trying to understand the reasoning by choosing a specific test approach when dealing with a simple A/B test - (i.e. two variations/groups with a binary respone (converted or not). As an example I ...
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Why does Stouffer's method work?

It seems like a fairly straightforward question, but when I really think about it, Stouffer's method doesn't make sense to me. This is why: Assume a two-tailed hypothesis. You first calculate $z_i$ ...
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About using the standard normal table

Suppose $\alpha=0.05$. How do I find the value $z_{\alpha/2}$ from a standard normal table? So $\alpha/2 = 0.025$. If I look the values $z=0.02$ and $z=0.03$ they are $0.5080$ and $0.5120$. I don't ...
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Transforming a Random Variable's distribution to Normal using Z-Scores

I have a random variable and many observations of that variable. The random variable is not normally distributed; its distribution is unknown. However, to analyze this variable and construct a time ...
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Equivalent of z-score in exponential distribution

I have an exponentially distributed set of data, but there are a number of outliers at the margin. If I want to identify samples above the mean that I am 99.9+% confident are not the result of ...
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What is Bartlett's theory?

This neuroimaging paper has been cited thousands of times. In it, a method is proposed for computing the correlations among several seed regions and all other brain voxels. Part of this method ...
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Z-score in the analysis of data

I am being provided z-scores of dependent and independent variables. I was checking if it can analyzed as such as raw data?
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Z Score for Non Normal Data [duplicate]

I am looking for some direction to see if there is an equivalent metric to a z score that could be used to quickly identify individual values in a non-normal distribution that are not likely to occur (...
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how to determine if a test run in only one geographic area leads to activity different than in other geographic areas

I was recently given data from an experiment that I did not design. In this study, the people running it changed behavior in 1 designative market area (DMA) but not the other DMAs (209 other DMAs). ...
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how to calculate a p-value for a null hypothesis given a z-score

I'm new to statistics and would love help with the following: Given an iid sample $X_1,...,X_{10}$ assume that $X_i\sim N(\mu,5)$. using the one-sample test we got a z-score of $2.2$. How do I ...
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Is there a way to define a statistic similar to the z-score for the Poisson distribution?

Let's say I want to compare samples taken from Poisson distributions that have different values of lambda (rate). If the samples were from a normal distribution, I could convert each observation into ...
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Testing the statistical significance of regression coefficients in a logistic regression

Are only the p-values relevant when testing the regression coefficients of a logistic regression? Does the z-value of a coefficient give any further information about the significance of the ...
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Question about probability of 0.99 that an average lies less than L years above overall mean

The duration of Alzheimer’s disease, from the onset of symptoms until death, ranges from 3 to 20 years, with a mean of 8 years and a standard deviation of 4 years. The administrator of a large medical ...
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Comparing within-subject z-scores (survey data)

I have some messy survey data, wherein one group of interest (cut on one self-reported behavior) rated every single attribute (7-point Likert scales) higher than any other group. I think this has ...
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Using t-test for feature selection after z-scoring data?

Suppose I have a high-dimensional dataset, and a binary classification problem. I want to use the two-sample t-test for feature selection. If the data has been normalized by z-scoring (so it has zero ...
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1 answer
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Wald test in logistic regression and its relationship to Z-statistic

If I have Z-statistic values in regression analysis, how can I convert them to Wald statistcs? Can Wald value be negative?
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1 answer
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Comparing Graduation Rates

I have multiple student graduation rates from the same school. Each year, there are variations in the student population and each year there are different graduation rates. Is there a way to compare ...
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1 answer
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Convert z-scores to percentile rank

Does anyone know the formula to convert a z-score to a percentile rank instead of using the z-score table? I searched the website, but did not find the formula. thank you
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9 votes
2 answers
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How can I find a Z score from a p-value?

How can I find a Z score from a p-value? I know how to look up the p-value from a Z score using a Normal distribution table, but I don't know how to calculate it. For example, a question says the ...
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Probability on Z-score

I have a data of 30 values that represent returns on investment and which have a mean of 7 and standard deviation of 14. We are talking here about normal distribution. Now I am being required to do a ...
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Z-scores, standardized tests and population means

I have been using z-scores by subtracting the mean (and then dividing by the SD) of the sample, whereas I recently read they actually need to be the population mean and SD. Assuming you are ...
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Triangular distribution

I am working on a dataset that ranges between 0 - 100 and typically is centered around 50 for the most part. It seems like the dataset shows a triangular distribution given its bound between 0 - 100. ...
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2 answers
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Will Z-scores help me compare my variables?

I have two variables: 1) Percentage of population of different geographic regions which has bought a certain category of product (say hair sprays) in the last MONTH 2) Percentage of population which ...
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Terminology - Comparing Z Scores

Let's say I have some sample of people with a measure of interest for each one, let's call it v. Let's say I measure v twice for ...
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How to report significance of factor levels shown in summary of glm?

The summary of my GLM shows day 12 of factor Date to be significant, but anova(model, test="Chisq") shows Date to be not significant overall. I know how to report the statistics from the Chisq table, ...
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Non-parametric z-score for comparison of outliers/extreme values across set of non-normal distributions

I have a network and for each node in the network I am calculating a certain property, essentially its 'connectedness' to a set of source nodes. In order to identify nodes which are better connected ...
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