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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27 views

How to determine 95% confidence interval for known population variance?

Consider group 1 only and suppose that the population variance is 12. What is the 95% confidence interval for population 1? Group 1 (Experimental Group) X bar 1 = 33 Sample size = 10 Population ...
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26 views

Way to make Z-Scores Positive

Hoping for some help with this. I need to calculate the the ranking for a number (eighty or so) groups, based on a number of component scores. Each component score is weighed. For example: Component ...
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1answer
38 views

comparing z scores from variables with different value range

I'm trying to understand z scores and how to use them. As far as I understand, I can use the z transformation to be able to compare different variables with different value range, that were not ...
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1answer
31 views

QQ plot comparison of z-normalized datasets

I want to make sure I'm correct in my assumptions. I'm predicting financial returns by using different ML models. There are 4500 values in each dataset. The density plots of all models are shown like ...
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1answer
47 views

How to convert data (percentages) into z-scores?

I have data for total population and percentage of smoking for 10 cities. The data look like below: How do I convert the percentage_smoke into z-score? Do I need to take into consideration of the ...
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1answer
38 views

Significance of differences between group-differences

Background: We have RNA-seq data (a method to quantify the expression of genes in a cell) from different cell types. These data were normalized using a method called TMM and then log2-transformed ...
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1answer
31 views

Calculating P-Value of a Z-Score without using Z-Table [duplicate]

I couldn't find any videos or documentation that shows how to calculate p-value of a z-score without using z-table. Isn't it possible or is it that hard? I know i can use scipy to get that ...
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1answer
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Validate Z-score Formula

I need need help validating a formula for a z-score. I have a book that I enjoy but in my re-read of the materials, I have found that the author has made some fundamental errors in their writing. So, ...
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1answer
27 views

From what type of distribution does observed z score come from, and based on this picture, what is the variance and mean?

I am trying to understand this conceptually and mathematically but somehow these formulas and variable expressions are confusing. If someone can explain it in simpler terms, it would be appreciated. I ...
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Confidence interval for the mean

If we want to create a confidence interval to estimate the mean of a specific population and we want the margin of error not to exceed $10$ at confidence level of $90\%$ given that some study suggests ...
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2answers
27 views

Transformed continuous variable Z-Score to Percentile

I had a non-normal distribution of my variable of interest which required log10-transformation to reduce outliers. This was then standardized, to a mean of 0 and sd of 1 (z-score?). I now want to ...
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1answer
48 views

How to normalize values but keep them all positive [closed]

I have an array of speed values that I would like to normalize. However, I need no value to be negative as I am doing a transformation of this data later on using division with revolutions per minute. ...
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How to compare outcomes of fantasy baseball statistics

My fantasy baseball league is head to head, weekly, with 12 categories. For each category you win (i.e., get more stats than your opponent) each week, you get one point, for a total of 12 possible ...
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1answer
28 views

Comparing survey data to passively measured data

Basic Situation: I have quite a large sample of around 10k people. In that sample I have two values for each person: a passively measured value of an amount of time, as well as their estimation of ...
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1answer
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Paired t Test on Z normalized values

I have 2 sets of data, each consist of 92 data points. Pearson's correlation between them is 0.22. My hypothesis is the data sets are not significantly different, so I've normalized each datasets with ...
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0answers
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Does Mahalanabis Distance have something to do with Min-Max normalisation? [duplicate]

Does Mahalanabis Distance have something to do with Min-Max normalisation? I know that it has something to do with Z-score normalisation, but when I tried Mahalanabis Distance on the Min-max ...
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1answer
37 views

Getting critical values - clarify solution [duplicate]

Two brands of coffee were compared. Two independent random samples of 50 people each were asked to taste either Brand A or Brand B coffee, and indicate whether they liked it or not. Eighty four ...
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1answer
46 views

p-value approach - clarify teacher's solution?

So I have a question with my teacher's solution below and I'm confused about one of the steps in their solution. I would appreciate some clarification. Two brands of coffee were compared. Two ...
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Calculate quantile using z-score in a normal distribution [duplicate]

I've got some z-score values and need to get the percentile (normal distribution) Of course I can use tables like: https://www.pindling.org/Math/Learning/Statistics/z_scores_table.htm But shouldn't ...
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1answer
37 views

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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1answer
57 views

Combining z-scores in clinical practice

I am a clinical neuropsychologist working with children with neurodevelopmental disorders. I have a quite naive question but we are unable to solve it with my colleagues (we are not very good in ...
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9 views

Equation for converting z-scores to percentiles [duplicate]

I need the mathematical formula for transforming z-scores into percentiles. I can't find it here or anywhere on the Web.
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1answer
34 views

Statistics probability help - can someone confirm my solution? [duplicate]

In a certain population, 15% of the people have Rh-negative blood. A blood bank serving this population receives 100 blood donors on a particular day. (a) What is the probability that 15 to 20 (...
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2answers
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Estimating population mean $\mu$ based on a sampling distribution

I've learned that under certain codnitions I can assume the mean of the distribution of sample means to be approx. equal to the real mean of the underlying population. Additionaly, the standard ...
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1answer
45 views

Find probability using Z-scores - don't understand solution

Graduate students applying for entrance to many universities must take a Miller Analogies Test. It is known that the test scores have a mean of 75 and a variance of 16. In 1990, 50 students applied ...
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Helpr finding the z-scores for several rows of numbers that represent different variables? [closed]

For example, if I had a table that looked like A. 1 2 3 4 B. 4 3 2 1 C. 2 2 1 3 D. 4 1 1 1 To find the Z score for Row/Variable A, would I use a mean of 2.5 (mean of row A) or a mean of 2.18 (...
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1answer
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How to normalize if variance is zero?

How do I normalize a dataset to z-scores is some features have variance zero? Is throwing them away beforehand the only solution?
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Why was the letter z chosen in z-scores?

Why was the letter z chosen in the name of a z-score = (data value minus mean) / standard deviation and not any other letter? This might be related to the same letter z being frequently used for the ...
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1answer
25 views

Use z-scores as measure for regression analysis/ANOVA

I want to calculate the difference between a certain value associated with a decision alternative and the value associated with the objectively correct alternative as a measure of decision accuracy in ...
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23 views

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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38 views

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
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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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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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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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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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1answer
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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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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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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
63 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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30 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
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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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1answer
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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
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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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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
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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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0answers
11 views

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
78 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 ...