Refers to the normal distribution, the Gaussian continuous probability distribution.

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Calculating standard deviations and testing the null hypothesis in a biological sample with n = 6

I am doing experiments on the viability of cells after treatment with different amounts of a certain substance. I have split my original cell line into 6 separate flasks at 3 days after unfreezing. ...
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3answers
132 views

Testing for specific normality in R

Is there a command in R, for which I can compare my specific sample to some specific (given) normal distribution? Like a qqnorm testing for the specific normal distribution ...
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1answer
48 views

Can you test for normality for a (0,1) bounded distribution?

I have a vector of observations called MyData which is a percentile score that is >= 0 and <= 1. I would like to test the ...
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1answer
28 views

Regression analysis and how to assess the assumption of normality of Y

I was told that to assess normality of Y in a regression, it is better to look at the residuals, rather than the conditional distribution of Y for each given X. My understanding is that both are ...
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1answer
30 views

Normality Test: Normality Test: Accept hypothesis null with uncertainty

I have the data of weight of a group of people after and before to a diet. I want to see if the weight loss distributed normal. ...
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14 views

Tail Bound from Asymptotics of an Estimators

Consider an non-parametric estimator for a random variable $X$ is $\hat{X}$. We know an asymptotic convergence for this estimator, in which $N^{1/4}\left(\hat{X} - X ...
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1answer
25 views

How can I analyze response data that is clustered around the ends and middle of a scale?

I have an experiment where I divide people up in to 4 conditions, give them 100 dollars and allow them to gamble any percentage of the $100 that they chose (50% chance of earning 2.5 as much as they ...
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3answers
86 views

Checking for normality with robust errors

I am running a linear regression (just a single IV) and have selected the robust error option (vce robust) in Stata due to heteroscedasticity (and because it is ...
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2answers
38 views

Testing for Normality

As part of an assignment I have to do a leakage study for a chemical product. We have been provided with data from 8 different batches, with 12 observations from each batch. The observed variable ...
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29 views

PROC ROBUSTREG or PROC NLMIXED in SAS, to down-weight effects of non-normality and outliers

We are conducting an OLS regression in SAS. We have performed all diagnostic tests and concluded that there is non-normality in the residuals, influential outliers and heteroskedasticity. We would now ...
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36 views

predictor skewed but normality of errors

In linear regression (linearity assumption had been checked), what is the effect if distribution of predictor is skewed but errors are normally distributed? Is there a risk for estimation of ...
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8 views

Problem using PermTest of the pgirmess package: Different p-values when rerunning PermTest on same lme

I am analyzing data of a decision-making task using anova(lme) for a linear mixed effecs model. To check for normality, I use the Shapiro-Test on the residuals of the model. In case of a significant ...
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2answers
37 views

Most appropriate analysis for non-normal, right-censored response variable?

I conducted an experiment with human subjects in which the independent variable has 3 treatment levels and the dependent variable is the duration of time that passes before the subject engages in a ...
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1answer
8 views

How to distinguish real price series from simulated series

Given a set of prices, I want to filter out series which are simulated from normal distribution from real prices observed in market. Is there a determining factor between real and simulated price ...
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1answer
914 views

Why is F-test so sensitive for the assumption of normality?

Why is the F-test for difference in variance so sensitive to the assumption of normal distribution, even for large $N$? I have tried to search the web and visited the library, but none of it gave any ...
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23 views

Linear regression with trimmed data

I would like to know how experts deal with real data. Even if statistical text books uses real data I'm always surprised how good the real data are and at the end of the exercises the residuals are ...
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36 views

Is the dataset Normally distributed?

So based from this link http://www.simafore.com/blog/bid/107702/2-ways-of-using-Naive-Bayes-classification-for-numeric-attributes I began to realize it might be a good idea to compute the pdf of ...
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1answer
43 views

Is there skew/kurtosis on this plot?

I'm doing a stats assignment and for one of the questions I need to make a judgement of whether there is skew and kurtosis from a p-p plot in SPSS. I've been over the lecture, and we were told to look ...
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20 views

Is this a 2 fixed unbalanced ANOVA? How can be tested normality and homoscedasticity?

I need to know if my biological experiments show discrepancies between the condition used. In my experiments I have 2 fixed conditions: type of substrate (2 types) and chemical added (1 control + 3 ...
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30 views

Four standard deviation rules in relation to normality testing

Within our department we were given a set of guidelines for how we might decide whether to proceed with parametric or non-parametric testing (for continuous data). These were drawn up in consultation ...
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19 views

is normality of raw data ever important? [duplicate]

http://www2.psychology.uiowa.edu/faculty/mordkoff/GradStats/part%201/I.07%20normal.pdf https://pubs.er.usgs.gov/publication/5224239 The two links above seem to me to claim the opposite. Is normality ...
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21 views

Normality testing for t test assumption

I am confused in what variables to input for normality, whether IV and DV go in together or seperately? I have an IV (high anxiety and low anxiety) and 6 dependant variables. When i check for ...
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1answer
27 views

Compare several means with different sample sizes (greater than 2)

I have seven different groups with different sample sizes and variances and I want to compare the means of their data. I'm not very informed in statistics, so could anyone help me out here? I've only ...
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25 views

Normality test in panel data analysis

Is it necessary to perform normality test such as Jarque Bera, Kolmogrove etc in panel data analysis? Assume I have 3000 obervation..Since the observation size is big, can I just assume that the data ...
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356 views

Is there an explanation for why there are so many natural phenomena that follow normal distribution?

I think this is a fascinating topic and I do not fully understand it. What law of physics makes so that so many natural phenomena have normal distribution? It would seem more intuitive that they would ...
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1answer
27 views

Pair t-test or Welch's t-test on a non-normal data series?

I have rainfall time series of 85 points from 1901-2013. I want to check whether the mean rainfall during 1901-1970 is significantly different than that of the mean rainfall during 1971-2013. Here, ...
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17 views

Normality and homogeneity test for small sample size

I would like to inquire if testing for normality and homogeneity is still necessary for my data from an experimental where trials were done only three times. Or can I directly perform ANOVA and ...
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1answer
26 views

ANOVA and Kruskal-Wallis Test in One Study

I am currently analyzing the results of my study which deals with several dependent variables. I have tested the data for normality and homogeneity and all but one passed the assumptions for ANOVA. ...
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1answer
50 views

How do you know if a distribution is normal? [duplicate]

Say I have a data set, how do I know if the distribution is normal or not? If not, how can I tell what type of distribution it is? Are there some tests for identifying distribution types?
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1answer
49 views

OLS Regression : Efficiency of the estimator of the variance of the residuals under the assumption of normality

My question is probably already answered somewhere but I did not find it. In the standard linear regression model under the assumption that residuals are normally distributed, we have a result ...
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10 views

Mixed effect models and data that has floor effects (and is proportions)(sort of)

I've been asked to analyze some data using linear mixed effect models (via lmer in R). However, I'm not sure this is the appropriate approach to the data. I am going to provide some background detail ...
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9 views

Help accounting for heteroskedasticity in a Revenue~GHG model with out Log transforming

Context I work for a sustainability charity and I've been developing regression model to estimate the Greenhouse Gas Emissions of public companies based on reported data (both financial and ...
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3answers
177 views

Statistical tests for uneven groups

We performed an experiment (usability testing), which had two independent samples, one group with 5 participants and the other with 24. Based on the analysis of the distribution of the data ...
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2answers
66 views

QQplot vs BoxPlot

I am having trouble reading my qqplots. I want to asses normality graphically before I carry out a test like shaparo test(my sample is small (<50)) . So I have two question is the qqplot better ...
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31 views

Shapiro-Wilk Normality Test

I am very new to statistics and need help interpreting a Shapiro-Wilk Normality Test. I have 2 data sets, one caled TMS and the other Placebo. I ran the test and got this back from R: ...
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32 views

Residual non-normality and prediction intervals

Normal residuals are generally understood to be necessary for valid prediction intervals in OLS regression -- but I've never seen a definitive guidance on just how much non-normality can be tolerated, ...
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2answers
115 views

Role of Central Limit Theorem in one-way ANOVA

Background: It has been shown and widely referenced (applets even exist, etc.) that for even a highly-skewed numeric variable, a sample size of $n\ge{}$30 is often "large enough" for the Central Limit ...
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34 views

Comparing two means (randomized experiment)

I'm kind of new to science :) for my thesis I worked on some study on health related behavior. There was an intervention for the experimental group and none for the control. So that seems to be a nice ...
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3answers
66 views

What type of data would have non-normal errors?

I'm trying to understand the assumptions for an OLS model. I get that the error term should be normally distributed if we want easy-to-calculate confidence intervals for our coefficient estimates. ...
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1answer
25 views

Normality test on logarithmic data

I had to take the log of my data, and now I want to test for normality of my data. Can I use the standard normality tests or do I have to use some special test? I used the ...
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42 views

Repeated-measures ANOVA vs. Friedman-Test (normality?)

I've four (paired) datasets consisting of 43 rows and want to check if there is statistically significant change between those groups. To see whether a repeated-measure anova or it's non-parametric ...
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23 views

Testing for normality - low p-value

I've a dataset with about 12k values given. It looks like this: When I try to test for normality I get following results, where p-value is extremely slow: ...
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2answers
59 views

Can I run a normality test on percentages?

First I'll start out with some background information. I conducted image analysis on 200 images to identify the area % of 7 different phases. I then averaged the results from each of for the 200 ...
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1answer
66 views

Do I have to test normality for both groups when comparing from a single population?

This should be an easy one. I'm a novice when it comes to statistics and English isn't my first language so bear with me. I have one population that numbers about 700. Of these 700, 25 are of special ...
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17 views

The Friedman's test

I have conducted research on the impact of toys on reading comprehension among primary school children. I have tested the strategy with three types of English language learners; good, intermediate and ...
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16 views

Test for Conditional Normality?

On page 357 of this article, it states: We assume that the treatment (or its transformation) has a normal distribution conditional on the covariates. How would I go about determining if a ...
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24 views

Asymptotic normality for nonsmooth objective functions

Assume that $f ({\bf x}; \theta): \mathbb{R}^p \times \Theta \to \mathbb{R}$, where ${\bf x}$ is the vector of inputs (with some distribution) and $\theta$ is the vector of parameters. Also, assume ...
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32 views

Correction for non-normal residuals where residuals are not correlated or show heteroskedasticity

I know the implication of non-normal residuals is uncertain statistical tests because the SEs are inefficient. Can I apply the Newey-West to calculate standardized Standard Errors for an OLS ...
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1answer
870 views

How incorrect is a regression model when assumptions are not met?

When fitting a regression model, what happens if the assumptions of the outputs are not met, specifically: What happens if the residuals are not homoscedastic? If the residuals show an increasing or ...
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1answer
25 views

Reference for standardizing non-normal variables for comparison

I need a reference to justify standardizing non-normal data. I will first explain what I am doing. I had a survey with ~30 questions. The answers to the questions were numeric; the range of possible ...