Refers to the conditions under which a statistics procedure yields valid estimates and/or inference. E.g., many statistical techniques require the assumption that the data are randomly sampled in some way. Theoretical results about estimators usually require assumptions about the data generating ...

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1answer
28 views

SEM (Structural equation modelling) Assumptions

I’m looking into SEM (Structural equation modelling using covariance matrixes) as an analysis technique and am finding it difficult to find consistent information on the assumptions of the technique. ...
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5answers
85 views

Why isn't independence checked standard in ANOVA?

The standard procedure for a one-way analysis of variance seems to be: fractile-diagram (or Q-Q plot) for checking normality Bartlet's test for heteroscedasticity But as standard I have never ...
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42 views

Checking the assumptions of K-means clustering

I want to do a k-means clustering on a dataset containing 22 numerical variables between 0 and 100 and 75 observations using R. I read this post How to understand the drawbacks of K-means on k-means ...
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0answers
32 views

Is polynomial regression restricted to linear models?

I'm wondering if polynomial regression extends to generalized linear models, so one could fit a model with a binomial, Poisson, gamma or other distributions? My question stems from a paper ...
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2answers
44 views

Does this mixed model violate assumptions of independence?

A disturbance event caused damage to 5 streams (Set1). To quantify this damage, five additional unimpacted streams (Set2) were picked for comparison. During the selection process every effort was ...
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2answers
844 views

Does the “No Free Lunch Theorem” apply to general statistical tests?

A woman I was working for asked me to do a one-way ANOVA on some data. I replied that the data were repeated measures (time series) data, and that I thought the assumption of independence was ...
2
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2answers
114 views

Am I breaking the assumptions of the Poisson distribution?

The Poisson distribution arises when events are counted within a specified interval. I've recorded the number of events each month (I'll not discuss what these events represent). This appears to meet ...
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0answers
27 views

How to do Cox regression if we have a variable which violates an assumption?

Is there a better way than stratification to do Cox regression for two variables, one qualitative and other quantitative, the qualitative (and more important one) violates an assumption of Cox ...
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0answers
43 views

Bonferroni Adjustment and Assumptions?

I'd just like to get clarification on something. When you perform a bonferroni adjustment (dividing the alpha level by the amount of tests you want to do, if say you're doing multiple ANOVAs) do you ...
2
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2answers
55 views

General assumptions about functions in machine learning

In the article "A few useful things to know about machine learning" (ungated pdf), I found the following quote: In fact, the general assumptions, like smoothness, similar examples have similar ...
3
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2answers
159 views

Error term in linear regression

I'm reading about a linear model which is fit to an equation, $Y = \beta_0 + \beta_1X + \varepsilon$, where $B_0$ is the intercept, $B_1$ the slope, and $\varepsilon$ the error term. My question is, ...
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2answers
534 views

Why is the normality of residuals “barely important at all” for the purpose of estimating the regression line?

Gelman and Hill (2006) write on p46 that: The regression assumption that is generally least important is that the errors are normally distributed. In fact, for the purpose of estimating the ...
3
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1answer
109 views

Linear regression with violated assumptions

I am trying to find out the determinants of cognitive function. The outcome variable is the mini–mental state examination which is a 30 point questionnaire response that has score values from 0 to ...
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0answers
102 views

Repeated measures ANOVA: what is the normality assumption?

I am confused about the normality assumption in repeated measures ANOVA. Specifically, I am wondering what kind of normality exactly should be satisfied. In reading the literature and the answers on ...
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0answers
33 views

assumptions to compute mahalanobis distance

Which are the assumptions to compute the Mahalanobis distance between two groups? Do all the variables of the two groups be normal distributed?
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1answer
66 views

loglinear analysis, assumptions met?

We've data from a large ongoing project at a big science museum. We are showing people plates of food where we vary the plate shape (round or square; 0,1), food arrangement (polygonal or vertical ...
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2answers
343 views

Assumptions to derive OLS estimator

Can someone briefly explain for me, why each of the six assumptions is needed in order to compute the OLS estimator? I found only about multicollinearity—that if it exists we cannot invert (X'X) ...
0
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1answer
28 views

LogLogistic Survival Model Assumptions

I am working with Hospital Length of stay data for the first time. It is highly right skewed. In researching ways to approach this problem, I thought a survival model fits the problem description. ...
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2answers
45 views

Errors and Residuals

In Wikipedia , it is written that : the sum of the residuals within a random sample is necessarily zero, and thus the residuals are necessarily not independent. The statistical errors on the other ...
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0answers
22 views

Data Assumptions for AIC model comparisons

I recently started digging into statistical information criteria, more specifically the Akaike Information Criterion. As the literature I have read so far does not cover this, I was wondering whether ...
2
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0answers
39 views

IIA assumption: difference logit and probit

Considering the following question about the Independence of Irrelevant Alternatives assumption: Alternatives to multinomial logistic regression It seems as if IIA is only a problem when using a ...
2
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0answers
60 views

When to use Brown-Forsythe Test?

I have been researching the differences between Welch ANOVA and Brown-Forsythe Test. I know that Welch ANOVA is used for more than two groups comparing whether there is statistically meaningful ...
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1answer
35 views

Log transformation for logistic regression

Is it necessary to log transform non-normally distributed variables to perform logistic regression? If so, when is it appropriate?
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0answers
38 views

PH assumption: categorical variable (1 category does not interact with time)

After checking the PH assumption in STATA I found one variable (4 categories, 1=ref.) to interact with time (using 'tvc'). The 3th and 4th category had p-values <0.05. However, the 2nd category did ...
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1answer
75 views

Consequences of violating assumptions of nonlinear regression when comparing models and/or datasets

I have a question about the consequences of using non-linear regression when the data violate the assumptions of (1) homoscedasticity and (2) normal distribution. Specifically, I am wondering about ...
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0answers
15 views

What assumptions does Wherry's correction make about the k x variables yielding obs R?

I think it makes 2 important assumptions that are rarely if ever met, leading to adj. R that is almost always an overcorrection of obs R. If I'm right, I think I can offer a fix to both problems. I'm ...
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0answers
22 views

Wild bootstrap in “bordeline" case t-test

I have to compare the mean levels of a continuos variable y (ranging 1-20) subdividing my sample in two groups according to a dichotomous variables (i.e gender). Sample sizes of the two groups are ...
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1answer
66 views

Would you ever *not* check model assumptions?

I have encountered a statistician who is suggesting that for secondary analyses, she would not check model assumptions (e.g., linearity, normality). Sample sizes for each group are 26 and 28, and this ...
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34 views

Is Wild Bootstrap a good strategy in General Linear Model (ANCOVA) with Assumption Violations (both normal residuals and homoscedasticy)?

I need to perform several GLM's (i.e. ANCOVA’s, with a single continuos dependent variable and several predictors, one dichotomous and some other continuos). I was looking for both a significance on ...
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0answers
15 views

Is there another way to make pretest scores in a Solomon design match?

As a research design, I applied the Solomon design, resulting in four groups: no pretest - manipulation A - post test no pretest - manipulation B - post test pretest - manipulation A - post ...
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1answer
41 views

Linear regression confidence intervals variance assumption in practice

An assumption for linear regression confidence intervals is that the variance is the same for the dependent variable for whatever of the independent variable. If in practice the variance is ...
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0answers
32 views

Checking assumptions of a large sample - extremely confused

I'm working with a sample size of over 2000 and I have become extremely confused at the first hurdle... I plan to run three linear regressions and one logistic regression. If I was working with a ...
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0answers
61 views

glmer - testing assumptions

I've used lme for my data and the assumptions about constant variance, normality, and independent observations are violated, so I took that as an indicator than I have to use glmer instead. Now I want ...
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0answers
30 views

What is going on here? Omnibus repeated measures ANOVA is marginal, but follow-up planned pairs <.05

I have a repeated measure ANOVA with a decent sample size (124 participants, with a score for each person for 3 conditions). The data are moderate to strongly positively skewed, (though similarly). ...
0
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1answer
83 views

What test(s) should I use to compare 2, non-normally distributed populations with unequal variances? (IV is 2 categories; DV is ordinal)

I'm a bit stumped as to what test(s) is/are most appropriate for the following scenario. I found a couple of similar questions but wasn't sure if the answers applied. For a report I am working on for ...
5
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1answer
94 views

Question about normality assumption of t-test

For t-tests, according to most texts there's an assumption that the population data is normally distributed. I don't see why that is. Doesn't a t-test only require that the sampling distribution of ...
2
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1answer
74 views

Help with understanding the assumptions of Wilcoxon signed rank test

I am comparing the monthly losses for actual and forecast losses for the same time period to see if our forecasts are in line with actuals. This is for a 12 month period. I am bit confused about the ...
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0answers
24 views

Can the chi-squared be used to test monthly means for two time series?

Can chi-squared test be applied to compare two continuous random variables but where instead of counts we split samples into groups and into cells of the table we put means for groups? In our case we ...
2
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0answers
59 views

Departures from normality in factorial design

This paper (http://psycnet.apa.org/journals/med/6/4/147/) states that departures from normality can be tolerated for one-way ANOVA. "The results give strong support for the robustness of the ...
2
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0answers
12 views

References for visually inspecting underlying model assumptions

In connection to this popular question in CV, I was wondering which peer-reviewed papers / books could be used as references about using visual inspection of q-q plots etc. as compared to performing ...
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0answers
24 views

When can one use Hochberg's or Hommel's method for adjusting P values?

The p.adjust function in R can produce P value adjustments based on methods from Hochberg and Hommel, which are both more powerful than methods from Bonferroni and ...
3
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1answer
101 views

Is this a Random or Purposive Sample? Inclusion-Exclusion Criteria and the Sampling Frame

Introduction I am confused about when a sample is a random sample (i.e. probability sample) and when it is a purposive sample (i.e. non-probability sample). My understanding is that the former allows ...
2
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2answers
104 views

Can my Bayesian prior reflect what the data should say rather than what it could say?

Can my Bayesian prior reflect what the data should say rather than what it could say? For example, assume I collect data where $Y_i$ is whether or not student $i$ passed the test and $X_i$ is whether ...
2
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1answer
88 views

Power analysis on chi-squared test with low cell counts

I am hoping to perform a chi-square test of independence on data in a 2x2 contingency table with the following values: ...
0
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0answers
15 views

Is it necessary for covariates in an ANCOVA model to be normally distributed? [duplicate]

I am running an ANCOVA model and am trying to remain true to all the statistical assumptions. I noticed that one of my covariates is not normally distributed, I know that the X and Y variables should ...
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0answers
38 views

Does negative binomial regression assume sample independence?

I'm working with a negative binomial multiple regression and I'm wondering about the assumption of spatial independence of samples. White and Bennetts (1996) say that the assumption of spatial ...
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0answers
41 views

Nonlinearity in OLS-models

I have a question connected to the OLS-Model's assumption of Linearity between parameters. What should be done if the assumption is not fulfilled? My second question is if I can use multinomial ...
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0answers
56 views

Can I interact my randomly-assigned variable with another variable in TSLS?

I'm working on an IV setup that uses random courtroom assignment as an instrument for whether a defendant goes to jail or not. (Similar to here and others). I have about five years of courtroom data, ...
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0answers
32 views

Is Naive Bayes robust?

We know that according to Naive Bayes assumption input features are assumed to be independent of each others given the target variable $y$. Now, If we intentionally add a duplicate (exact copy of ...
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2answers
93 views

Can a one-way ANOVA be performed in these circumstances

I am supporting a psychology experiment, and having problems analyzing some of the data. By way of background, I’m a programmer at a research organization who’s taken several stat courses recently. ...