Questions tagged [parametric]

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I want to show by simulation that the Wilcoxon test is more robust than the Student test for non-normally distributed data

I want to test by simulation that the Wilcoxon test is more robust than the Student test for non-normally distributed data. For example, I'm testing the ...
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21 views

Interpreting AFT Model Coefficients: Mean vs. Median Survival Time in Log-Normal Distribution

When interpreting the coefficients of an Accelerated Failure Time (AFT) model that assumes a log-normal distribution, should we focus on the impact of coefficients on the mean survival time or the ...
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1 vote
94 views

Parametric copulas with marginals that are regressions

In Dependence Modeling with Copulas (Harry Joe) I'm struggling to interpret the meaning of a statement. In Chaper 5.1, it is stated: Parametric inference for copulas For dependence modeling with ...
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1 vote
76 views

Which statistical test is appropriate to compare two parametric bootstrap samples drawn from model fits of two time series?

In previous threads , parametric bootstrapping was suggested as a method to test for differences between time series at specific time points. I have followed the methods as described in this answer (...
1 vote
103 views

Can multicollinearity of parametric terms in a GAM be ignored?

I've had such a hard time finding a source that addresses how to handle multicollinearity of parametric terms in a generalized additive model (GAM) that I'm starting to think it may not be important, ...
• 1,539
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Parametric or non parametric mixed effect models for very small sample size in ecological/soil data?

I am running an ecological/environmental experiment in a salt marsh with 5 experimental treatments and 3 replicate soil samples taken from each treatment. I have been taking measurements from these ...
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22 views

Estimators that are superefficient on a dense set

In Chapter 8 of van der Vaart's Asymptotic Statistics, it is shown that (under weak regularity conditions) an estimator can be "superefficient" on at most a set of Lebesgue measure zero (...
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1 vote
153 views

Parametric vs Non-parametric test recommendation

What type of non-parametric test would be suitable for the dataset shown in the image: The sample size is 200 each for both variables. The data value can vary from 0-4 for both variables. The ...
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130 views

If I have a very small n for one group and a very large number of features, should I choose a parametric or a non-parametric test?

I have a dataset that contains human metabolite concetration in a fluid. One group has about 12 samples, while another only has 5. My question is if I can assume normality for this data and do ANOVA/t-...
9 views

Central tendency to present in table in relation to hypothesis test

I am doing hypothesis test on the data to compare group A and B and there are multiple variables that I tested. Due to the distribution of some of these variables is skewed and there are some extreme ...
18 views

Must an alpha=0.01 be used to interpret significance of parametric terms in a GAM?

I have fit a time-series count HGAM with environmental covariates as parametric terms and year as a site-varying smooth term. I am wondering if I need to use an alpha threshold of 0.01 to interpret ...
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378 views

GAM - parametric coefficients - what is mgcViz::pterm() actually plotting?

I built a GAM with two categorical variables and two smooth terms, following this structure: ...
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24 views

Is there a statistical test for five groups with averages ONLY?

The data I collected was measuring plant shoot masses and these were extremely small, so I could only find the total mass of the shoots from 30 plants. Hence, I only have the mean and none of the ...
111 views

Fisher Z transformation still not normal

I have 18 different groups that I need to compare. I used the raw values from a neuroimaging file to represent synchronization between two brain regions (which ranged from 0 to 1) and Fisher Z ...
1 vote
255 views

How to interpret the partial effect plots for parametric terms while using gratia::draw() and gratia::parametric_effects()?

I am asking a question akin to this one: https://stackoverflow.com/questions/71884457/what-does-the-y-axis-effect-mean-after-using-gratiadraw-for-a-gam but am wondering the same question for ...
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56 views

Importance of normality testing in clinical trials / AB tests

I’m curious to read about the importance of normality testing in AB tests and clinical trials. It seems that there is a lot of mixed (and strong) opinions about the necessity for normality testing, ...
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48 views

Are there families of known parametric copulas for non-standard marginal normal distributions?

I know that a family of Gaussian copulas generates a standard bivariate normal distribution if and only if the marginal ones are standard normal. This characterizes the Gaussian copulas, where I have ...
1 vote
331 views

residuals in parametric survival analysis

This is probably a straight-forward question but I can't find a straight-forward answer. The topic is new to me. I am performing parametric survival analysis, e.g. estimating a survival function from ...
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938 views

Example of a parametric test with no normality assumptions?

I read an article saying that "all parametric tests make an assumption of normality", which I know to be incorrect, since technically a parametric test could be done for any distribution, ...
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1 vote
63 views

How do I sample new data for a parametric bootstrap with linear regression?

I initially have two data vectors $x$ and $y$, where $y$ is assumed to fit the linear model $y = \beta_0 + \beta_1x + \epsilon$, with $\epsilon \sim N(0,\sigma^2)$. I fit the model using fitlm in ...
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138 views

How to parameterize covariates in parametric time to event model (lognormal distribution)

I have a parametric time to event model for survival data and I found that a lognormal distribution has the lowest objective function value for a base model. Below is the hazard function for the ...
13 views

If linear regression is parametric, do we need normality of the features and/or target? [duplicate]

From what I know, linear regression is a parametric model (as mentioned in here). Parametric tests requires normality of the variables. My first question is that this is an assumption of the linear ...
1 vote
19 views

Mapping Parametric Curves with auxiliary variables

The image below displays an approach of using an auxiliary variable to map the parametric curves of a standard normal pdf and cdf. In Equation (1), z as r.v. is clearly one-dimensional. However, after ...
1 vote
683 views

Comparing before and after survey using Likert Scale

We are trying to measure if there is a difference on the level of interests of participants before and after I let them play a game. The survey is in the form of Likert Scale where ...
353 views

Use of both parametric and non-parametric tests in the same study

Suppose we are investigating whether there is a significant difference in dependent variables A and B between two treatments in a population. Let's assume that the data provide parametric assumptions (...
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Correlated linear survival model

I'm trying to model a survival situation like the following: Say I have 100 data points, and each will survive some number of days before dying at some point. In my problem I know that over a span of ...
174 views

How to handle assumptions of statistical tests?

Does any definitive work exist, e.g. a review, a book chapter, or a book, on the advantages and disadvantages of existing approaches? Is there a consensus on which approach is the right one? I have ...
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115 views

Predicting time to event / duration data

I've built a parametric survival model (survreg in R) to predict injury recovery duration using features such as age and treatments. I'm looking at trying model-based boosting using mboost with ...
• 1
701 views

Is Kernel-Regression parametric or non-parametric?

As the title says, is kernel regression a parametric or non-parametric method, and how can this be motivated/explained?
55 views

Why are parametric models usually robust to mild misspecification?

Statisticians often use parametric families of models, for example normal distributions with unknown mean and variance. However, nothing in real life is perfectly normally distributed (or distributed ...
76 views

Power calculation for two populations of equal variance

If I had a scientific assay which when run on a control population produces readouts which are normally distributed about the mean. A treatment which changes this mean does not change the variance of ...
169 views

Independent Sample T-test or Mann-Whitney U test?

I am a very young stats learner, and I need help understanding the justification of a test choice. I have a sample of 39 participants (20 females and 19 males) been measured on task performance, and I ...
1 vote
20 views

Example of a parametric family of distributions that always has dependence on among its variables

Inspired by this question, I would like an example of a parametric family of distributions such that there is dependence for all choices of parameters. The family could be infinite or finite, but I ...
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139 views

Are there any parametric machine learnig models that can represent non-linear behaviour between a predictor and a targe variable?

Some basic models, like multiple linear regression (MLR), are parametric but usually limited to linear interactions between X and y. Other models can represent non-linear interactions between X and y, ...
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5k views

Why are parametric tests more powerful than non-parametric tests?

I'd like to understand why parametric tests are more powerful than their non-parametric alternatives. Is the word choice of "power" the same as statistical power? As I understand it, power ...
• 1,539
444 views

Which test should I use to compare a normal distribution sample with skewed distribution sample?

I have two groups : Infection group (n=26) and healthy control group (n=127). The aim is to see if there is a difference in the mean of T cells absolute count* values between the two groups. Ho= the ...
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1 vote
88 views

Survey sampling: How many participants per group (current, former, and potential users) should we recruit?

We are designing research in which we will explore the perception of users (C current, F former, and P potential) on a product. We apply the same questionnaire for each group adapting (verb tenses) ...
45 views

What repeated measures statistical tests should I use with uneven sample size and parametrical/nonparametrical distribution?

I'm looking for a way to measure significance + variance homogeneity/heterogenity First of all I tested my data for normality and it's not always parametrical, so I think that I should use different ...
465 views

When is a hypothesis test appropriate? [closed]

For example, when would a hypothesis test bed used?
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147 views

Data didn't pass normality testing for K-W and S-W but the skew and kurtosis were within range...advice please?

I am conducting a study on the relationship between rural/urban living, intentions and barriers to help seeking in adult males. I was planning to conduct a correlation and then pending that result, a ...
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