# assumptions's questions - Chinese 1answer

598 assumptions questions.

### 11 Why is high positive kurtosis problematic for hypothesis tests?

I've heard (sorry cannot provide a link to a text, something I have been told) that a high positive kurtosis of residuals can be problematic for accurate hypothesis tests and confidence intervals (and ...

### Linear model - positively correlated errors and predictors vs negatively correlated errors and predictors

I know the answer is likely to be 'it depends,' but I was just wondering.. in linear regression, which usually is considered worse in the following two cases and why? case 1) presence of correlated ...

### Checking the Assumptions for T-tests

I am in the porcess of checking the assumptions of some data in order to perform a T-Test and had a few questions about how they should be set up. I was able to find the assumptions for a T-test here....

### 1 What are the assumptions of linear regression (both simple and multiple) [on hold]

I know this is a basic question, but I get slightly different answers everywhere I look, a quick example is that I learnt at Uni that the errors of the dependent variable have to be normally ...

### 15 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 ...

### 2 Why do copulas need the i.i.d assumption for marginal distribution?

1 answers, 389 views assumptions copula iid
Does anyone know if are there some assumptions for Copula method? I heard from someone that the data should be i.i.d (independent and identically distributed). Let's say, if I want to capture the ...

### 2 Assumption of homoscedasticity/equal variance violated in a 2-way ANOVA

I'm analyzing results from an experiment where 56 samples were tested for a specific response to electrical stimulation. Electrical stimulation was done at 2 different stimulation frequencies, and at ...

### 1 Panel data: predictor variables with different observation times/frequencies

I would like to estimate a standard logit (panel data): $\text{logit}(P(y_{i,t}=1))= \alpha + \beta_1 x^1_{i,t} + \beta_2 x^2_{i,t} +\epsilon_{i,t}$. The problem I am facing, however, is that $x^2$ ...

### 1 How to handle differences of neocortical parcellations between groups

In my lab, we are currently looking at how two handedness groups (mixed handed and consistent handed) differ in terms of lGI (local Gyrification Index, a cortical folding measure) across 74 different ...

### 3 Assumptions for Canonical Correspondence analysis

I have been trying to find the major assumptions a Canonical Correspondence Analysis makes when doing its analysis. I have had a hard time finding anything useful. I did, however, find the assumptions ...

### 1 How to fix serial correlation in a cross sectional data set

I am doing my thesis at the moment and I needed to check the BLUE assumptions for my data set. I am doing my thesis on trying to explain IPO underpricing and my data set consists of 100 companies who ...

### 5 Significant output in Levene's test for equality of variances in MANOVA; what to do?

1 answers, 1.646 views spss assumptions manova levenes-test
I want to perform a MANOVA in SPSS as follows: i have a independent variable that consists of three groups (- of which the group sizes are not equal), and six dependent variables. When checking the ...

### 1 ANCOVA - Non-linearity of covariate

I have a dataset where I calculated genetic distances between populations of some animals (a continuous variable). I want to know if these differences are explained by physical or/and ecological ...

### 4 Why are statistical assumptions not reported in published journal articles?

0 answers, 47 views model assumptions
In universitiy theses I often see students including details about their model in the appendix (distribution residuals, heteroscedasticity, durbin watson, multicolinearity values). However in ...

### 18 Practically speaking, how do people handle ANOVA when the data doesn't quite meet assumptions?

4 answers, 7.241 views anova heteroscedasticity assumptions
This isn't a strictly stats question--I can read all the textbooks about ANOVA assumptions--I'm trying to figure out how actual working analysts handle data that doesn't quite meet the assumptions. I'...

### 3 When are the linear regression parameters of Y and X the same as the parameters of Y' and X'?

2 answers, 53 views regression assumptions derivative
I am working on some simple linear modeling of a physical system and assumed that taking the derivative of an equation $$Y = \beta_1 + \beta_2 X + \varepsilon$$ would give me \frac{dY}{dt} = \...

### Poisson assumptions

I am dealing with a dependent variable that is either 0, 1 or 2 in theory it is unbounded and it can take values more than 2 so I am motivated to test Poisson model first. The frequency counts for ...

### 2 How to implement a regression with non-independent observations in the DV?

I have a design where a number of object pairs were rated for association strength. These pairwise association ratings along 5 criteria of interest are expected to be used as IVs in a regression. ...

### 1 Can someone enlighten me on what is “Neglected Nonlinearity”?

I ask this question out of curiosity earlier today when i was trying to test for heteroscedasticity in R, i accidentally mistook ...

### 2 Is it possible to derive joint probabilities from marginals with assumptions about the conditionals?

2 answers, 106 views assumptions joint-distribution marginal
I understand the title is too generic. I tried to look for similar questions and although there were a few that were seemingly about the same issue, either they provided answers in the negative or had ...

### 6 Is “ independent and identically distributed” an assumption or a fact ?

4 answers, 2.180 views independence assumptions iid
This is in the context of two random variables. A frequent assumption (e.g. of the error term in ANOVA) is of independent and identically distributed random variables. There is a question on this site ...

### 3 confusion about the link between residuals, error terms, sample size and CLT in ANOVA

I feel a little confused about the assumption of the ANOVA and what it ensures mathematically the errors have to be iid and normally distributed N(0,1). independance of observation. Is it not a ...

### 2 Unequal sample sizes one-way ANOVA [duplicate]

2 answers, 1.627 views anova spss heteroscedasticity assumptions
I have a question about a data analysis that I am running. I am analyzing the results of a survey in which (expectedly) there exists far fewer people in one group than in another. This survey is an ...

### 2 Model assumption redundancy on simple linear regression

I'm stuck on some subtleties involved in simple linear regression formulation. In a very general fashion I understood that the optimal point forecast for a random variable $Y$ (in terms of MSE ...

### 14 What is the need of assumptions in linear regression?

5 answers, 1.904 views regression assumptions
In linear regression, we make the following assumptions The mean of the response, $E(Y_i)$, at each set of values of the predictors, $(x_{1i}, x_{2i},…)$, is a Linear function of the predictors. The ...

### 5 How to account for multiple measurements of same person in either two-group comparision or regression?

I am running analysis on clinical data collected from patients which are correlated either by time (longitudinally) or more commonly different measurements of the same person at same time (eg. ...

### Friedman test when subjects are not a random sample from a population/ when subjects are dependent

Imagine that you measure all $n$ people from a school class in $k$ $\geq2$ different treatment conditions. My goal is to find out whether the there is a systematic difference in Ranks (i.e. the $H_0$ ...

### 2 Assumptions made in Poisson distribution

I was going through Poisson distribution and I understand the other assumptions made in Poisson distribution except for the last one which is: The probability of an event in a small sub-interval is ...

### 1 Multicollinearity and predictive performance

Looking at this statement: "Multicollinearity does not affect the predictive power but individual predictor variable’s impact on the response variable could be calculated wrongly." Is this ...

### 3 Which model assumptions are important for prediction?

1 answers, 33 views prediction assumptions
Disguised as other questions, there are frequent questions where the OP checks for violations of model assumptions (e.g. normality, homogeneity of variance in linear regression) in models they intend ...

0 answers, 22 views regression independence assumptions
I did regression analysis. It's about incoming calls and amount of orders. I got a result like this. summary(ireg) Call: lm(formula = 1/sqrt(ie) ~ ia + id) Residuals: ...

### Assumptions of the Friedman Rank Test

Let $X_i:= (X_{i,1}, ..., X_{i,k})$ for $i =1...n$ be $\mathbb{R}^k$-valued random Variables with $k\geq2$. I wonder what the exact assumptions are to apply the Friedman test to Realisations of ...

### Bayesian Additive Regression Trees - model assumptions?

BART builds on regression and classification tree models, and you can use it for continuous and binary outcomes (=probit). See Chipman 2010 for details. With normal regression methods there are a ...

### Regression assumption

I have a data set where $100$ people made $500$ trips for $5$ days. I want to build a trip-level regression (zero-inflated Poisson) where the dependent variable will be the count of hard-braking in ...

### Assumption tests to be run on each independent variable or on the entire model in a multiple linear regression?

Here are important assumptions that one has to check when performing a linear Assumption 1: Homoscedasticity of residuals or equal variance (with Breusch-Pagan test for example) Assumption 2: ...

### Assumption of ARIMA and relation to ARCH/GARCH model?

I only have a very basic understanding of time series analysis. As I am learning ARIMA and then ARCH/GARCH models, I have some subtle (at least for me) questions on the common procedure to build such ...

### 10 Why does repeated measures ANOVA assume sphericity?

Why does repeated measures ANOVA assume sphericity? By sphericity I mean the assumption that the variance of all pairwise differences between groups should be the same. In particular, I don't ...

### 1 Evaluating Mann-Kendall trend test assumptions

Disclaimer: I don't have very much statistics experience.. I do have yearly climate data (yearly max temperature, total yearly precipitation...) for 200 years and want to perform the Mann-Kendall ...

### 5 Does the proportional hazards assumption still matter if the covariate is time-dependent?

If I estimate a Cox Proportional Hazards model and my covariate of interest is dependent (continuous or categorical), does the proportional hazards assumption still matter? I recently went to a ...

### What are the prerequisites before running Holt Winters Model?

I just read Demand-Driven Forecasting: A Structured Approach to Forecasting(Wiley and SAS Business Series) and have a few doubts in Holt-Winters Model: 1) Unlike OLS Regression Modeling technique or ...

### 3 How to check if the random effects in a random effect model are uncorrelated with the input variables?

Some asked before "Why do random effect models require the effects to be uncorrelated with the input variables, while fixed effect models allow correlation?" My question is: how do you check this ...

### 1 What happens with Mahalanobis-Distance, when the assumption of equal Covariance-Matrices breaks down

Assume that we want to compare the forecast quality of various forecasters $f$ on $n$ values such as stock-market prices or whatever. We could then define a "Mahalanobis-Distance" (MD) (or rather ...

### 34 Why are survival times assumed to be exponentially distributed?

10 answers, 4.751 views distributions survival assumptions exponential
I am learning survival analysis from this post on UCLA IDRE and got tripped up at section 1.2.1. The tutorial says: ... if the survival times were known to be exponentially distributed, then the ...

### Levene's test significant in 2x3 mixed design ANOVA

I'm trying to run a 2x3 mixed design ANOVA. Participants were measured on three different domains at two different times. One out of the 6 sets of results violates Levene's test while the rest do not. ...

### Deviations from normal distribution

0 answers, 21 views anova multiple-regression assumptions
I'm conducting multiple regression analyses using a sample of around 1200 participants. I'm first trying to identify relevant covariates to include in my model, in which I'm using ANOVA, t-tests, and ...

### Does sample size needs to be consider in the correlation between a proportion and a ranked variable?

I'm looking for the correlation between a rank variable A and the proportion of blue (variable B) among 3 types of colour: blue, ...

### 18 What tests do I use to confirm that residuals are normally distributed?

I have some data which looks from plotting a graph of residuals vs time almost normal but I want to be sure. How can I test for normality of error residuals?

### bayesian analysis on normal distribution - robustness of the variance

I am doing bayesian inference on normal data, and wonder how robust are the results with respects to some assumptions and potential mistakes. Specifically, for simplicity I want to assume that ...

### 18 Assumptions of multiple regression: how is normality assumption different from constant variance assumption?

5 answers, 1.819 views regression multiple-regression assumptions
I read that these are the conditions for using the multiple regression model: the residuals of the model are nearly normal, the variability of the residuals is nearly constant the residuals are ...

### 5 Survival analysis and Fisher's exact test contradicting results

1 answers, 414 views survival assumptions fishers-exact
I'm looking at a dataset of survival times of animals in two different groups. While there is some early mortality in the first group, the Kaplan-Meier survival curves overlap, the log-rank test and ...