The normality tag has no wiki summary.
3
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1answer
73 views
How to test for normality of growth disturbances in chemo treatment?
I'm a med student, conducting a retrospective analysis of weight/growth disturbances during chemo treatment.
I wonder, if I should:
assume, that growth is a variable normally distributed across the ...
0
votes
0answers
22 views
Modelling a skewed, 10-point Satisfaction variable
I am trying to replicate and hopefully improve on an analysis done in a study to find determinants of patient satisfaction after shoulder surgery. Satisfaction is heavily skewed (with over 60% of ...
1
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2answers
60 views
Should the predictor variables be normally distributed for Poisson glm?
This is probably a really basic question, but it's the first time I've created a model that defines Poisson as its error family.
In setting up my variables to make the model, should I be concerned ...
2
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2answers
79 views
What is the expected distribution of residuals in a generalized linear model?
I am performing a generalized linear model, where I have to specify a family different from the normal one.
What is the expected distribution of residuals?
For example, should the residuals be ...
0
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1answer
93 views
What statistical test to use for my questionnaire
I have to do some statistical tests on a questionnaire and don't know which tests i need to do. The questionnaire have been marked as right or wrong and I have about 60 peoples results. The tests i ...
1
vote
1answer
87 views
All my observations are identical. Use a non-parametric test?
I was doing test for normality on variables and came across one that had identical values for each observation. I can't do a normality test. I plotted the kernel density and it looks normal, however ...
3
votes
1answer
107 views
QQ plot is consistent with normality when subgroups are non-normal
I have read that for a one way ANOVA, you should check that the model residuals are normally distributed. If the variance of each group is homogeneous then this implies that the residuals with each ...
5
votes
2answers
246 views
QQ plot does not match histogram
I have a histogram, kernel density and a fitted normal distribution of financial log returns, which are transformed into losses (signs are changed), and a normal QQ plot of these data:
The QQ plot ...
3
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3answers
232 views
Normality assumption and sample size
I know this is a very debated topic, even on this site, but I still couldn't find an answer to my problem.
Recently I am working with large samples (300, 400 and more). For now, I am trying to use ...
2
votes
1answer
74 views
Shapiro test and transformation
I am playing with shapiro.test from R and checking for non-normality of error variance.
...
1
vote
1answer
343 views
Can non normal data be used for factor analysis and multiple regression? If so what is the procedure to justify it?
While I was writing up the analysis in my thesis, I just came across when rechecking my test for normality, that the p-value for most continuous variables was .000, which is less than .05, and it ...
1
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0answers
142 views
Comparing observed and predicted values across several measurements
As a neuropsychology graduate student with some experience in statistics (I'm usually the guy other psychologists come to with statistics problems after trying it themselves but before seeing a ...
4
votes
1answer
237 views
Disagreement between normality tests and histogram graphs
My data consist of compaction measurements from 3 different cell types (X,Y, and Z). My goal is to know whether there are "significant" differences between these measurements, so I have tested for:
...
2
votes
1answer
100 views
Which test to use to compare means/medians when one variable has normal distribution and the other does not?
Which 2-tailed test is best to use to compare means/medians when one variable has a normal distribution and the other does not?
7
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2answers
215 views
Simple question about the asymptotics of estimators
Consider any arbitrary estimator called $\hat{M}$ (e.g., regression coefficient estimator or specific type of correlation estimator, etc) that satisfies the following asymptotic property:
...
5
votes
2answers
706 views
Normality of residuals vs sample data; what about t-tests?
An addition to the common confusion about normality testing in inferential statistics for general linear models:
I understand the assumption of normality refers to the residuals in ANOVA and ...
1
vote
2answers
349 views
Required conditions for using a t-test
The conditions that I have learned are as follows:
If the sample size less than 15 a t-test is permissible if the sample is roughly symmetric, single peak, and has no outliers.
If the sample size ...
4
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2answers
143 views
Does a zig-zagging residual plot mean that normality has been violated?
I have the following diagnostic plot for my data. Is normality violated, especially given the zig zagging residual plots?
0
votes
1answer
468 views
Normality test for anova mixed model in SPSS: I did it in two ways but the results are contrasting
I'm conducting an ANOVA mixed model 2 X 3 (group X condition). Right now, I'm checking for the assumptions of ANOVA, such as normality. I should check indipendently for group and condition, right? I ...
7
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2answers
322 views
Transformation to increase kurtosis and skewness of normal r.v
I'm working on an algorithm that relies on the fact that observations $Y$s are normally distributed, and I would like to test the robustness of the algorithm to this assumption empirically.
To do ...
0
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1answer
189 views
Non parametric test on unequal groups and repeated measures data
I am recording animal behaviour in four different conditions but in the same environment. So my data are several values (the number of which vary) representing the frequency of a single behaviour for ...
2
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1answer
142 views
Sum of normally distributed variables is a normally distributed variable?
Consider two Wiener processes:
$$
\begin{aligned}
X_a &\sim\mathcal N(0,a) \\
X_{a-b} &\sim\mathcal N(0,a-b)
\end{aligned}
$$
How do I show that:
$$
X_a - X_{a-b} \sim\mathcal N(.,.)
$$
That ...
3
votes
1answer
397 views
Using Student or Wilcoxon test on small sample without information on the normality of distribution
I have three subjects in a qualitative study. I am comparing the features of their writing before and after treatment.
I have no idea about the normality of the distribution since they were selected ...
16
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2answers
462 views
Can we see shape of normal curve somewhere in nature?
I do not want to know if some phenomena in nature have normal distribution, but whether we can somewhere see shape of normal curve as we can see it for example in Galton box. See this figure from ...
1
vote
1answer
147 views
How robust are multivariate methods to violations of normality? [closed]
In many cases, multivariate methods are used without normality tests.
How are following methods robust if data are not normal?
Principal components analysis
Canonical correlations analysis
Factor ...
3
votes
0answers
255 views
Is the Anderson-Darling test or Shapiro-Wilk test more powerful? [closed]
In the testing of normality, how would the 2 compare? Is one significantly better than the other?
1
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0answers
132 views
Significant factor in 2-way repeated ANOVA becomes not significant in 3-way repeated ANOVA?
My research design is 2(Ear) x 3(Factor A) x 3(Factor B) with repeated measures on all factors. For 2 way-repeated ANOVA, I used laterality index (normal distribution, calculated from % of responses ...
5
votes
2answers
445 views
Normalization vs. scaling
What is the difference between data 'Normalization' and data 'Scaling'? Till now I thought both terms refers to same process but now I realize there is something more that I don't know/understand. ...
5
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5answers
763 views
How to determine whether data is slightly or extremely non-normally distributed?
I'm a PhD student and doing a research on regression analysis.
My question is how to determine whether the data is slightly, moderately or extremely non-normally distributed?
4
votes
1answer
315 views
What kinds of variables should we use the normality test for?
When should we apply normality tests? For which types of the variables should we apply the normality test?
For example dependent variables, independent variables, or control variables, etc?
5
votes
3answers
239 views
Is there any test for a null hypothesis of non-normality?
I'm currently looking for a test having for null hypothesis that the sample does not come from observing a normally distributed random variable. In other words, I'd like to know if there's a test ...
1
vote
2answers
325 views
Skewness, kurtosis and normality of a time series
I have a sample size of $21$ with $496$ observations.Can I presume an approximately normal distribution,and use a $t$-test to compare the difference in means, and difference in various financial ...
4
votes
2answers
579 views
Is the sample variance a useful measure for non-normal data?
Does it ever make sense to compare the variance for two sets of data, neither of which are even approximately normal (e.g. bimodal)?
1
vote
2answers
2k views
Testing normality assumptions for linear mixed models and mixed (repeated) GLM ANOVA in SPSS
I have a mixed design that includes both repeated (condition) and between (sex and genotype) subjects factors. I would like to assess whether my data meets the normality assumptions for 1) General ...
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0answers
95 views
How to transform a highly leptocurtic distribution to a normal distribution? [closed]
How to transform a leptocurtic distribution into a normal distribution
1
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2answers
1k views
Can I use a Z-score with skewed and non-normal data?
I've been working with some process cycle time data and scaling using the standard z-score in order to compare between parts of the full cycle time.
Should I use some other transformation since the ...
1
vote
3answers
355 views
Does the non-normality matter in using regression for prediction?
Does the non-normality matter in using regression for prediction?
Hi all,
In the QQ plot of the residuals after linear regression, the residuals turned out to be highly non-Gaussian.
Most of the ...
1
vote
2answers
275 views
Impact of regression normality-assumption on model comparison & prediction?
This question is a continuation of the discussion here:
How to test the statistical significance for categorical variable in linear regression?
Following Macro's suggestion, I started a new thread.
...
2
votes
1answer
240 views
What happens if you reject normality of residuals when estimating with least square ?
What happens if you reject normality of residuals when estimating with least square ?
Is it too important to have normality on the residuals?
2
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2answers
2k views
Repeated measures ANOVA or Friedman test?
I have a study with 35 subjects who received hypercoagulability testing at 4 different times (before surgery, after, at 1 week, and at 1 month). Each subject has 9 different test of hyper ...
3
votes
2answers
3k views
How robust is ANOVA when group sizes are unequal and residuals are not normally distributed?
I understand that there are degrees of trust one can have in the output of ANOVA. However, naturally I want to maximize the amount I can trust my results.
Question: If I have data that violate the ...
4
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2answers
2k views
How to test for normality in a 2x2 ANOVA?
Study Design: I showed participants some information about sea-level rise, focusing the information in different ways, both in terms of the time-scale and the magnitude of potential rise. Thus I had a ...
1
vote
1answer
286 views
Shapiro-Francia test error
I'm trying to run a normality test on the residuals after fitting a mixed-effect model (with lmer). I read that the Shapiro-Francia test can deal with data with more than 5000 observations (I have ...
5
votes
4answers
243 views
How to verify that simulated data is normally distributed?
I have a program generating purportedly normal distributions and I would like to test it. I have a number of issues; perhaps the experts here will help me sort out the essential from the inessential ...
1
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0answers
158 views
about test for multivariate normality with kolmogorov-smirnov test and $\chi^2$ test in R program [closed]
how can I test for multivariate normality with kolmogorov-smirnov test and $\chi^2$ test in R program?
2
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3answers
1k views
How robust is ANOVA to violations of normality?
I have several dependant variables that are non normal in distribution: Kolmogorov-Smirnov test is significant, skewness ranges up to 8 for some variable, and kurtosis is generally about 2 but in a ...
1
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2answers
112 views
Transformation by subtraction (for continuous data arbitrarily limited in the experiment)
Consider a study looking at the relationship of chili-pepper plant height to number of chilies produced.
Data was collected on all plants taller than 10cm. Initial look at the distribution of ...
1
vote
1answer
316 views
What's a good normality test for time-series / sleep data?
I have data that is, at its most basic level, activity counts per minute of fruit flies. Flies are considered to be asleep when they have no activity for at least 5 minutes. The data essentially looks ...
3
votes
3answers
2k views
Checking normality of a Likert scaling question
I have likert scale responses (1-5 rating) of 20 respondents for a set of 25 questions. So that means that each respondent has answered 25 questions (with 1-5 rating). If I need to check the normality ...
0
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1answer
212 views
Using secondary data require normality test?
I am undergraduate student and I have a problem in my research. Recently, my supervisor told me that if using secondary data no need to perform normality test, why? It is got any citation or previous ...
