# All Questions

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### Numerical integration of a function of an empirical CDF

I have the following equation $y = f(x)$ and I want to invert $f(\cdot)$ to find $x$ numerically. Because the function $f(\cdot)$ is quite complex I will solve $y - f(x) = 0$ instead, using the ...
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### Poisson regression with offset vs logistic regression

I am thinking to use Poisson regression with an offset variable instead of a logistic regression in case where event is rare, since p (probability of success) is very small and n (sample size is ...
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### Can we do use convenience and purposive sampling at the same time?

Easy accessibility as the reason for choosing the participants but at the same time samples that have been purposely selected
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### How to deal with interaction between several dummy variables and one continuous variables in one or two regression models?

I want to know the relationship between revenue and cost in several conditions. Dependent variables is REVENUE.REVENUE is a continuous variable from 0~1000+.I have several key independent variables: ...
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### How to perform multiclass SVM classification using k-fold cross-validation and SMO with some kernel method in MATLAB?

I have data matrix X.csv file of size nxd, where n are the observations, and d variables. There are c_1,..., c_m classes. Let, Y be the matrix containing the class labels. There is no header row in ...
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### Convergence in hidden markov model

I have a HMM where forward-backward probability increases in Iteration 1, then it decreases and then increases (as well as converges). Probability values after iterations 0,1,2,3,4 are: ...
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### Proving that largest root (obtained via P.C.A.) is a symmetric function [on hold]

Suppose, we are given $\textbf{X} = (X_1, X_2, \ldots,X_m)$ and $\textbf{Y} = (Y_1, Y_2, \ldots, Y_n)$. Also, we are given, S = pooled variance. If we implement Principal Component Analysis (P.C.A.) ...
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### What is the alternate hypothesis of the null hypothesis β_1=β_2=β_3=0?

Usually with simple hypotheses I will have something like $$H_0: \beta_1 = 0 | H_A: \beta_1 \ne 0$$ But suppose I have a null hypotheis $$H_0: \beta_1 = \beta_2 = \beta_3 = 0$$ Question What is ...
12 views

### Reduction of models

In a normal linear model, I have working with 3 categorical factors, $A, B, C$, and my main model is the interactions model $A*B*C$. My question is as follows: If i wanted to see how far I can ...
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### Feature selection for an ordered logit model (R)

I'm using an ordered logit model to predict credit ratings/risk (1-8, ordinal) as a function of 126 predictor variables. (See: https://www.kaggle.com/c/prudential-life-insurance-assessment/data for ...
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### Non-parametric density estimation: Is it better to estimate a PDF by first finding its CDF?

By better I mean fewer density error against the true PDF. Say that $X$ is the random variable that we wish to find its true PDF $f_X$ by the estimation $\hat f_X$. Then my goal is to find $\hat f_X$ ...
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### Principal Component Analysis: Scale reliability and validity

I'm using a popular psychometric scale, the Domain Specific Risk Taking (DoSpeRT) scale, that contains 30 items that measure an individual's risk taking capacity across five different dimensions: ...
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### What statistical tests to compare two AUCs from two models on the same dataset?

Let say I build two machine learning classifiers, A and B, on the same dataset. I obtain the ROC curves for both A and B, and the AUCs value. What statistical tests should I use to compare these ...
11 views

### Applying Cox Proportional Hazards Model on Discontinuous Variable

I am using coxph in Rstudio to apply Cox Proportional hazards model on my data. This model is easy to use on continuous variable ...
31 views

### Is this controversial that in PCA, we want the variance as large as possible, while in bayesian, a large variance means a low precision?

I am wondering about the variance. We say the variance is inverse proportional to precision, then we also say the variance is proportional to the information, which means that a large variance means ...
12 views

### Neural net and new data shape

I am studying machine learning, and trying to follow the neural net implementation in this book, but I am having problems with the net effectively rejecting the dimensions of my own dataset. In the ...
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### R cut zero-length interval [migrated]

I have a column that has numeric values in the 1--7 range. I would like to use the cut function to split these values into the following intervals: 1 -> 1, ...
30 views

### Is imputation needed for $0$'s in regression?

I am working on a dataset of 2000 records using SAS Enterprise Miner in order to predict insurance payment (compensation) from insurer, a motor insurance company, to its customers. Though there are no ...
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### How to assess the significant level of a sample difference per number of element

I have 3 samples of 28 paired elements which have been tested for normality and they are not normal due to biomodal distributions. I carried out a Friedman test and is not significant. However I know ...
287 views

### Should I use an average to summarize ordinal data?

I need to work out a "average" (for lack of knowing a better word) of ratings or perhaps I could call them labels. Basically, I have a list of words that have been rated 1 - 3 for difficulty. 1 being ...
12 views

### Neural Network - Learning accuracy drops heavily after a couple of epochs

I designed a neural network to classify some images into 28 classes. Here are the parameters : Weight Decay : 0.005 Momentum : 0.01 Learning Rate : 0.001 and 0.005 Learning Decay : 1 Input : 100x100 ...
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### How to update latent discrete variables in MCMC?

Most of the discussion on Bayesian model with latent variables that I've seen fall into two classes: continuous latent variable underlying the observed discrete outcome (e.g. probit model (Albert ...
26 views

### Heteroskedasticity Question

I have a model that's affected by Heteroskedasticity: bptest(m1) studentized Breusch-Pagan test data: m1 BP = 65.055, ...
15 views

### Regression Using Surveys with Unequal Number of Responses

I am trying to figure out how to properly do regression analysis on a data set from a peer-review survey where individuals in the survey have an unequal number of responses. Below is description of my ...
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### Generalized model with different kinds of variables

I'm working with captive jaguars behavioral data to answer how several independent variables affect the incidence of a certain behavior "E". My dependent variable is the number of times the behavior E ...
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### Logistic Regression: Should I include a non-significant variable that notably increases the OR of a significant variable?

I am studying the effect of different pollutants on the probability of a genetic mutation. My binary logistic regression models are as follows: Model 1: Dependent variable: genetic mutation (binary ...
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### How many parameters required to approximate quadratic function with NN

How many layers do you need to build a RELU network (1-layer or deep) to approximate x^2 function on [0,1] with 1e-6 accuracy. What is the practical result on the same, say with Tensorflow ...