# 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 ...
1 vote
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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: ...
1 vote
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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 ...
1 vote
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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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### 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 ...
2k views

### 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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1 vote
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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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1 vote
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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 ...
5k views

### 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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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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### 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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### 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. ...
1 vote
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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 ...