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Questions tagged [z-score]

The z-score of an observation is the number of standard deviations above or below the mean of the distribution of observations from which it came.

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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 Find the PROPORTION of a population for a STANDARD NORMAL between infinity and 1.25? [closed]

i am practicing how to find Z score and i want to know how to find Zscore for infinity. because Z score table does not have that value.
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10 views

Standard normal distribution vs Unit normal distribution

Are the Standard normal distribution and Unit normal distribution describe exactly the same? Or they describe different things?
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31 views

Condition for using z-scores to evaluate data points [closed]

If the population is Gaussian distributed, then can you always use the z-score to see if certain data point is larger than x percentage of the population? In other words, is the method valid for a ...
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Fitting distributions using the dispersion of Z-scores

I work for a medical testing company and I've inherited some legacy code written by someone who has since left. I understand the reasoning behind most of what is there, but the final step is something ...
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1answer
19 views

two binomial distributions of widely different size - confidence intervals, p-values or z-scores?

I was hoping for a bit of help. I have two very different sized samples of binomial distribution, and I want to figure out if they are significantly different. A previous question posted on here has ...
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Group mean&SD with respect to which z-scores are computed

I have a research report that gives the standardised test scores from a number of subjects. However, it is not specified with respect to which group the z-scoring was made. Thus, for each subject ...
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34 views

Why z-score/standard score is a linear transformation

Can someone please help me understand why the standard score $(X - \mu)/\sigma$ is a linear transformation since both mean and standard deviation depend on X?
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Measuring relative variability for variables with different scales II

I'm reformulating this question to see if I might have better luck than OP did at encouraging a response. Consider that you have two univariate datasets at different scales, and need to establish ...
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13 views

Comparing a Z-score from a model fit on real data against a randomized input

I have a quite complex statistical model that fits the parameter $X$ for some input data. The form of this model is irrelevant for the further question (at least I think so). Let's say I provide two ...
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13 views

Modified Z score of a sample

I would like advice on how to calculate a modified Z score for multiple samples drawn from a population. I understand that when working with standard Z score the standard error of the mean woudl be ...
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23 views

Using exponential smoothing with modified z score

I am finding anomalies in my data. My data contains exit rate of a website for the last 3 years with a daily frequency. When using just modified Z score & finding anomalies, it does not take ...
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1answer
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regression with z-scores as composite variables?

So I have 5 IV's- a,b,c,d,e and one DV. a is fine as is. b & c measure the same concept and since their ranges are the same, I averaged the scores to create a composite variable. d & e ...
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modified z score

I am using Modified Z-Score to find out outliers on a time series data on exit rate for a website. N = 1131. Based on last 3 years daily data (1096 values), i am finding out outliers for the ...
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1answer
31 views

What is the ideal population size so that its median is a representative statistical measure? [closed]

I am perfoming a robust z-score analysis to remove trends of temporal evolution of a certain variable so that I can compare different years. It is robust because there are outliers. My data is ...
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1answer
32 views

Probability for high z-scores

Where can I find a z-table (or app or whatever) that will give me the probability associated with very high z-scores (e.g. 12 or 15)?
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118 views

Calculating P-value for multivariate normal distributions?

I'm given a set of 500 ($\sigma_i, \mu_i$) that define a 500-dimensional multivariate normal distribution, where each dimension is effectively independent from all the others. Given a 500-...
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Should I standardize my variable for regression before nonlinear feature transformation?

I would like to fit a non-linear model by doing nonlinear feature transformation first (e.g. exp, log) and then using linear regression (or regularized linear regression). However, I am stuck at ...
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Models and standard scores

I'd like to use standard scores to describe a variable $y$. If I always measured $y$ in a particular place and time, I'd just take the mean and standard deviation of $y$ and then calculate the ...
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1answer
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Just want a quick confirmation on a simple normal distribution problem

Given mean = 167cm, standard deviation is 3cm, a) When four are randomly selected, all of their heights will be greater than 170? b) When four are randomly selected, two will have heights smaller ...
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1answer
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Help understanding this admissions statement!

The statement reads: "applicants invited to interview will be based on the z scores of their MCAT total score percentile and their GPA combined in a 2:3 ratio." From what I understand is that GPA ...
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1answer
50 views

Z-score and Hypothesis Testing [closed]

I have a large dataset of vehicles's speeds. My goal is to infer an upper bound on the (average) speed of the population of all vehicles $U$ The way this is to be done is like this: Given a potential ...
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1answer
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Calculate score for multiple variables [closed]

My question is similar to this. I have a large geographical area divided into small cells (approximately 2.25 km$^2$). I'm calculating some value (heat) for individual cells dynamically. It is an ...
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1answer
23 views

Mapping Significance Level to Z-Scores

Does a mapping (e.g. a table) exist, to map Z-scores to significance levels? For the Normal Distribution, a Z-score of 1.96 corresponds to the 0.05 significance level. How can the significance level ...
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1answer
36 views

Z-score for weighted proportion

I have a question regarding the Z-Score test when it comes to compare two proportions. Usually, one would use this formula to obtain the Z-Score: and then compare it to a Standard Normal ...
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1answer
102 views

Why reject Null Hypothesis when p value< alpha? [duplicate]

As per statistical literature, there seems to be this understanding that given a p value less than alpha, we are to reject the null hypothesis. The way I am interpreting this is that is the critical ...
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1answer
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Z Score Values Used and Interpretation

I have been working on a time series-like data set from using calcium indicators (waveform data). A script I was given transforms the voltages (x values) into Z-scores. However, the mean and standard ...
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1answer
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Simple Z-Score question dealing with normal mean and standard deviation I keep getting incorrect

The question below is simple, however, I got the question wrong despite following a basic formula I have been using for a while now. Here's the question: For applicants who actually entered medical ...
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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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1answer
254 views

Can I average z-scores for basic insights?

everyone. I'm new to this so perhaps my question will sound elementary but hopefully you can help. I have a data set that contains student test scores across several learning areas (English, Biology ...
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Why does the Y axis change in population density plot when changing from raw scores to z-scores (assuming normal distribution) [duplicate]

Why do values on the Y-axis change in a probability density plot when changing from raw values to z-scores? The mean z-score aligns with 0.40 on the Y-axis, while the Y-value for the mean with ...
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1answer
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Why the z-scores values stays mostly between -3 and 3?

I was reading through the Google Machine learning crash course and I can't digest the below point: Scaling with Z scores means that most scaled values will be between $-3$ and $+3,$ but a few values ...
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2answers
20 views

Hypothesis Test for a Proportion. Z-score = -44

I got $n = 8000$, and I get a z-score of $-44$. How do I deal with this? How do I find the probability if I can't look this up in the Z-table?
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1answer
51 views

Normal Distribution using Z - Score Rules

The distribution of heights of adult men in the U.S. is approximately normal with mean 69 inches and standard deviation 2.5 inches. Use what you know about a normal distribution and the 68-95-99.7 ...
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1answer
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Bounded Anomaly Score between 0 and 1

I am using a KNN anomaly detection approach, where the distance to my nearest neighbor is an indication for an anomaly. I am wondering how I can normalize the score between 0 and 1. I can use a test ...
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1answer
43 views

How to determine Density Value of a Z-Score?

In this paper the authors are demonstrating the conversion of Ordinal data to Interval data. In the Step No. 7 on Page 360, they are talking about Density values of corresponding Z-values. They are ...
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1answer
107 views

Is there a method to transform all z-scores into positive values?

During my calculations I need to use square roots but z-scores can be negative. Is there a trick to transform them into positive value without missing the usefulness of z-scores? What if I have not ...
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Standardize then subtract or subtract then standardize?

I have data as follows: Variable1: baseline score Variable2: score after treatment The two variables have the same units. I want to normalize and standardize the scores. For normalization, the ...
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1answer
120 views

When are real limits used for calculating z score?

I'm taking an introductory statistics course. At first, the textbook talks about real limits in the context of continuous variables and frequency distribution table, that is all clear. But on what ...
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1answer
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using z scores to compare and average player values from different fantasy hockey analyses?

I'm VERY bad at math - but am trying to find the right statistical technique to use to build a cheat sheet for my fantasy hockey draft. Here's my proposed approach - but I'm hoping for feedback to ...
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397 views

Why would I use Min/Max scaling over Z-Score?

If I'm using a prediction model which uses a distance-based metric to help calculate class separability, why would I use Min/Max over the Z-Score? I've always thought Z-Score as superior because ...
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Compute p-value for very high z scores [duplicate]

For a statistical test I need to compute the p-value given a z score. I am using the Python method: scipy.stats.norm.cdf the problem is that for z score > 8, ...
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Intuitive explanation for t vs z in confidence intervals

Skip to the conclusion if TL;DR What is an intuitive explanation for what a t-score gives you when computing confidence intervals? Background of my understanding of confidence intervals I just ...
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When to normalize data when using two datasets from the same distribution?

Suppose you have two datasets D1 and D2. Both are sampled from the same underlying distribution X. I want to use them to train a neural network. The features are all unsigned integers in range [0; 2^...
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can you transform spearmans r into pearsons r for meta analysis

my meta analysis involves the calculation of overall effect size based on pearsons r correlations within studies. I am already converting the pearsons r to fishers z scores for analysis but I have a ...
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How do I calculate sensitivity Index d' from a model statistics

I did a supervised classification on EEG data. The resulting BCILAB ML models have 5 fold cross validation and here are the statistics. ...
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25 views

Using Z scores of subgroups of a population to determine significance

I am working with several exams in which there are known conversions from raw score to Z-score for each individual based on previous population data. I am working with a sample group that, as a group, ...
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Scaling results from two events of different sizes

I am working on a scaling and comparison problem from the sporting world. For each event I am calculating a z-score for each competitors results and I am looking to use these corresponding p values ...
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Topic assignment in a topic document matrix. How to be robust?

I have a Document-Topic matrix whose scores were produced by multiplying a Topic-Term matrix produced by non-negative matrix factorization on a Term-Term matrix and the original Document-Term matrix ...
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Combining Z Scores by Weighted Average. Sanity Check Please?

I'm trying to measure how "exceptional" a particular observation is based on several attributes of that observation among a population of observations. Each observation has several attributes, all ...