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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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Comparing z-scores, one variable pre-/post test

I am working on an assignment where I am going to compare a group of students test scores measured in a pre-test with the same group of students test scores measured in a post test. Due to the way ...
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Comparing two z-score variables

Say I have 2 variables (height and weight) for 20 people. Each height and weight value will be converted into a z-score (calculated using age and gender dependent population norms). Weight and ...
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3answers
40 views

Z-scores for different size groups

I want to know how I can calculate the Z-scores for groups with different sizes? Let me try to explain: We have a city with 100.000 inhabitans. The city is divided in 10 neighborhoods, all with ...
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9 views

Comparing regression/correlation values within-subjects? Repeated Measures ANOVA afters Fishers Transform?

I was interested in the most appropriate way to assess whether there is a difference in the R values from a regression analysis in a repeated measures design. I transformed my R values using a ...
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7 views

Scoring the difference between a family of distributions and a test distribution

Let's suppose we have a random model that I can sample to generate distributions of a certain 1D variable. I want to score the distance of a test distribution to the model in question. The distance ...
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0answers
29 views

Probability of getting two $z$-scores that are within one standard deviation of each other

Randomly choose two $z$-scores following a normal distribution with mean 0 and standard deviation 1.* What is the probability that the $z$-scores are within one standard deviation of each other?
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clustering analysis\ data is in right skewed

what normalization technique(mean normalization/min max/zscore) is prefered to apply k-means clustering scope of data: right skewed variables are different scales & magnitude(days,counts) ...
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9 views

Confused about z-score image normalization output

I am trying to normalize my input data for a convolutional network, I applied the z-score normalization technique to my image dataset as follows: Formula: (image - mean(image)) / std(image) ...
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ANOVA or T-TESTS on Z-SCORED data

Let's assume that we have results from X people for 3 different variables. The scores are not on the same scale (for example they're not scores on the test when you can simply reach from 0-10 points). ...
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19 views

How to get confidence interval for a z-score/percentile of an individual observation?

Let's say I want to calculate a z-score or a percentile of one subject with respect to a target population. To calculate it is easy, however I have only a sample from this population, so although I ...
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1answer
52 views

Comparison of two normal distribution

I have two normally distributed samples. I want to know how close or similar it is. I tried few methods to find the similarity, like z-score and bhattacharyya distance. Bhattacharyya distance didn't ...
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25 views

Standardization based on subsamples

I need to analyze data on the cognitive performance in a sample of participants divided into clinical (36 participants) and non-clinical groups (~100 participants). What would be the correct ...
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2answers
32 views

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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1answer
24 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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0answers
32 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
23 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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2answers
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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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0answers
12 views

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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0answers
15 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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0answers
57 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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32 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
60 views

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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0answers
111 views

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
35 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
42 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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222 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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40 views

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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0answers
55 views

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
22 views

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
43 views

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
51 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
25 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
52 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
148 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
22 views

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
33 views

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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241 views

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
344 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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0answers
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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
75 views

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
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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
109 views

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
48 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
151 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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28 views

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 ...