# All Questions

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### svd adds value before an elastic net model?

I learned that SVD eliminates redundancies. If you use an elastic net model, is it still greedy as stepwise models in general? or the fact that it has penalization factors reduces the greedy ...
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### How do I apply MDS analysis on my data set?

Consider the following dataset (it is the emission probability matrix of a Hidden Markov Model): ...
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### Probabilistic model Vs Weight based model

Can someone please explain what is the difference between probabilistic model vs weight based model with respect to ML context. When to use one over the other?
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### Troubles reporting transformed variables for log and sqrt into a general equation

Good morning everybody, I see CrossValidated has really high level of questions and answer; I am just a student so I hope this question is not too basic... Suggestion of further readings available ...
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### Free Throw Probability

I was asked this in an interview today. Would you rather try to make 2/3 free throws or 4/6? Why? I reasoned that if my chance of making an individual shot was > 2/3, I would go for 4/6 because it ...
29 views

### Multi Output Neural Networks

Up until know I only used neural networks to classify a single output, I set one output neuron for each class and check which neuron has the highest/lowest activation. What I am trying to do is to ...
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### Expectation of squared non zero-mean data w.r.t. two distributions

I have the following model: $\hat{d}_i=a_i+b_i+c$, where $a_i$ is a zero-mean Gaussian r.v., $b_i$ is a r.v of unknown distribution, and $c$ is a constant. I want to estimate ...
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### Understanding the variance to mean power function in Poisson gamma models

I have a biology background and try to understand what it means that the distribution of snps over the genome follows a Poisson gamma (PG) model. It is accepted that each chromosome contains Poisson ...
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### Best way to graph probabilities of feature vectors

I have a lot of feature vectors in the form of: v1=[x0, x1, x2, x3, x4] where x0, x1, and x2 can take binary values. either 0 or 1 x3 and x4 can take values from 0 up to 9 I have a lot of vectors ...
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### References and Best practices for setting seeds in pseudo-Random Number Generation

In this document, that concerns the "set seed" command, Stata people discuss issues related to the setting of seeds when generating pseudo-random numbers. A notable "don't" is "don't use serially ...
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### Need help setting up multilevel logistic regression

I am trying to see the effect of a certain intervention in schools. The outcome variable is binary. We have students within schools. Also students' age is a covariate (doesn't changed before and after ...
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### Which is correct way for regression line?

I have a set of data (some Frequencies per month, Var1 is the month): ...
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### Approximating cox model with time varying covariates using poisson

How do you reformat a dataset in order to perform a cox regression with time-varying covariates as a poisson regression. I'm trying to run a survival analysis regression in python with time varying ...
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### Minimum variance for sum of three random variables

I have been working on the following problem: Given you have VarX = 1, VarY = 4, and VarZ = 25, what is the minimum possible variance for the random variable W = X + Y + Z, or min Var(X+Y+Z)? My ...
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### Survival using SPSS [on hold]

I have a database of about 50 subjects. Each subject received a number of implants (2-7 per patient). Therefore, there is one row per subject. I have a column for number of implants. I have another ...
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### Help finding critical on a hypothesis contrast

I´ve tried finding the variance using the moment-generating function but apparently that is not the correct method for finding the critical. Can you help me with this?
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### Could you please suggest a newbie about publishing Statistics related papers?

First of all pardon me if this is not the right place to ask something like this. If it is not the right place then I'll request you to let me know where I can discuss such things related to academia. ...
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### Help in finding the joint distribution

There is a metric $H$ defined as = $\sum_{i=1, j \neq i}^{N} \min |u_i - u_j| * ..*|u_{i+d-1} - u_{j+d-1}|$ where $u$ is a multi dimensional vector of dimension $d$ and $u_i,u_j$ $\in \mathcal{R}^d$ ...
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### How can I implement lasso in R using optim function

As you know lasso is a popular variable selection method of the form of $(y-x\beta)'(y-X\beta)+\lambda \sum_i|\beta_i|$ the first is that it is possible to use optim() function in R to minimize ...
32 views

### Detecting a trend to increase, in a time series, in real time

Probably, someone who's into technical analysis of share prices eats stuff like this for breakfast. Me, I couldn't devise a theoretically acceptable approach. I have this thing (private working set, ...
22 views

### Expected numbers of distinct colors when drawing without replacement

Consider an urn containing $N$ balls of $P$ different colors, with $p_i$ being the proportion of balls of color $i$ among the $N$ balls ($\sum_i p_i = 1$). I draw $n \leq N$ balls from the urn without ...
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### Adding predictor variables and/ or systematic judgement to time series forecasts

I have a ways to go with my forecasting general education --- but I'm doing a seasonal time-series forecast for predicting sales order volumes. It's mostly software sales, which does have a ...
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### Determine accuracy distributions from measurements

Is it possible to determine the distribution of a certain measurement accuracy if one have a serie of measurements, carried out under fluctuating conditions, and the accuracy of the measurement ...
15 views

### What does the intercept correspond in the Anova() function in R?

I've been struggling to understand what the intercept sums of squares and p-value correspond to when I run a one-way ANOVA with Type "III" sums of squares using the Anova() function in the car ...
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### Finding a hypothesis test based on the Neyman-Pearson about a parameter with a piecewise density function

I'm having trouble about how to start this problem. The density function for a random variable $X$ is:  f(x|\theta) = \begin{cases} \frac{1}{2(1+x-\theta)^2} & \text{$if x \ge \theta$} \\ ...
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### t test for slope with binary variable

Cosider two random samples: one from the variable $Y_1$, with $n_1$ observations and the other one from the variable $Y_2$ with $n_2$ observations. Let $\mu_1$ and $\mu_2$ be the sample means of ...
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### Interpreting a linear mixed effect model's interaction term

I am a biologist and am attempting to analyze the effects of time and location on depth. I was told I needed to use a mixed effects model to account for the random variables of Individual and tracking ...
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### What is a good model for a regression analysis having TF-IDF dependent variable?

I am trying to build some models for a multivariate regression analysis that have as dependent variable TF-IDF values for some terms extracted from textual documents. An important characteristic of my ...
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### Multivariate Regression on Multicollinear Categorical Variables

I am working on a dataset with a continuous response (which could be dichotomized), one continuous covariate, and multiple categorical variables. The continuous covariate (weight) is directly ...
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### Test equality of two measurements for a outcome

I have a binary outcome which were measured with two methods say A and B such a $2\times 2$ table like this: ...
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### compute Expectation Propagation messages for sum

Can anyone help me in understanding how Expectation Propagation updates are computed when we have a function on several variables? Like this example: ...
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### Early stopping methods for ANN applied to series prediction

Could anyone give advice or links to advice on early stopping methods for ANN trained with back prop applied to time series prediction? I know some methods for classification tasks but don't the ...
27 views

### Questions about non-standard test statistic for difference of two population proportions

Background I'm considering the number of observed 'successes' $x_1$ and $x_2$ from $n_1$ and $n_2$ independent trials respectively. These counts can be considered realisations of random variables ...
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### Peak Hours for Tweeting

I am trying to figure out the peak hours during a 24 hour period for my companies twitter account. We are trying to find the sweet spot to optimize our interactions (RT+Replies+Favorites). I have ...
23 views

### Neural Network for hand written digit recognition

I have create the neural network with three layers. 1 layer - 500 inputs 2 layer - 500 inputs 3 layer - 10 output classes. I have synthesized the ...
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### Which type of feature scaling to use [duplicate]

I've been writing some simple machine learning algorithms and looking at time-series data. In doing so, I have come across the use of feature scaling: rescaling and standardizing as they are referred ...
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### How to cluster data with repeated measurements?

Most clustering algorithms assume that data points in each row are independent. I have some data with repeated measurements from individuals. I can use a standard algorithm, and then check to see if ...