# All Questions

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### How to sample when you don't know the distribution

I'm fairly new to statistics (a handful of beginner-level Uni courses) and was wondering about sampling from unknown distributions. Specifically, if you have no idea about the underlying distribution, ...
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### Cannot intuitively grasp “Standard normal deviate”

I cannot intuitively grasp the meaning of "Standard normal deviates". I think It would help if you provided me with either/all of the following: (i) real life examples of their application, (ii) an ...
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### Tobit versus OLS

There is a dependent variable which is measured in £ and can take the form of £0-£100,000. It is effectively the value of the payment made. If it takes the form of £0 it means a payment was not made ...
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### Expected lifetime of a device with two parts each having spares?

Consider a device with two parts : (1) and (2). Part (1) has 2 spares and part (2) has one spare. Lifetime of part (1) and its spares have iid exponential distribution with rate lambda. Lifetime of ...
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### Estimating a probability distribution with a discrete and continuous part

This is a question more for advice and a suggested starting point than anything else (though anything else is cool as well ) The data that I have is something like this - 1,000,000 data points of ...
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### Significant autocorrelation in time series decomposition random component

I'm very new to time series analysis. The data below represents about 8 years of aggregate daily visitors to some tourist attractions. I'm trying to examine the random component of some time series ...
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### Correlation of latent variables: Sum-scores vs. SEM correlation

I use a set of about 20 attitudinal items. My aim is to investigate if these items represent a number of dimensions and to what extent these dimensions are correlated. Exploratory factor analysis ...
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### Some doubts about using time random effect

I'm starting with lme4 and GLMM. Maybe this question can be basic for experimented researchers, but I'm still learning. I have a pooled data where every ...
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### Error “initial value in 'vmmin' is not finite” when changing factors in ordinal logistic regression

I've generated some fake data to give a simple example of ordinal logistic regression. My data set (raw data here) looks like this: ...
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### test to be applied

I have applied 3 treatments at 10 different concentrations of each on a bacteria to see if they affect its existence. my response variable is binary i.e. 1 for effective and 0 for ineffective. basic ...
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### Statistical arbitrage using eigen portfolios

I was trying to understand below paper https://www.math.nyu.edu/faculty/avellane/AvellanedaLeeStatArb071108.pdf Page 20 explains about "Entering a trade". I wan't to know clearly what it means to ...
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### Repeated measures - sum of biomassproduction

I am student in biology. For my examination I conducted a greenhouse experiment with gras. Actually I am not sure how to develop the correct model and unfortunately I haven't found an answer in the ...
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### Impute missing data of a variable

I'm currently working on spatial spillovers in agriculture at the municpal level with cross-section data. But, I do have missing values for the investment in capital at the municipalities though the ...
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### SVM with pre-computed kernel and zero bias

I have an optimization function, where I need to give my own kernel matrix and bias value is zero. The kernel matrix is calculated using the data but there is no specific formula for it. If I have a ...
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### Machine Learning and Biostatistics

I am interested in a few areas with biostatistics, and was reading the course catalog at a university that offers machine learning. I am taking topology now, and i think machine learning uses ...
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### What is the meaning of the R factanal output?

What does all this mean? I'm a factor analysis 'noob' and although I've read a book, it didn't tell me everything apparently. Since the chi square statistic is so high and the p-value so low, it ...
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### Is there a way to add inequality constraints on the LASSO in R?

I am trying to use LASSO for model selection, but I need my fitted values to remain non-negative. Is there a way to implement this simply in R? I've found that the penalized package allows for non ...
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### How to test adjusted mean in R?

I have got eight adjusted means for eight subgroups in a survey study, but I don't know how to test the differences of these eight adjusted means. Any suggestion is appreciated. Thanks!
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### Benchmark datasets for testing multiple regression or multivariate regression model?

I have a question as a newbie. I'm working on a tool using regression analysis( linear, multiple, multivariate) to derive a regression model. To verify the correctness of the tool, I'm trying to find ...
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### Simple Trend Question in Excel [on hold]

I am just using the simple trend function in Excel. I am confused by the bold value below for 2013. Why the increase? 11 Y values 11 X values The final two are the predictions. Y = 1118.69791 ...
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### test interactions for multiple regression with many predictor variables

I have a data set with around 25 predictor variables. If I am planning to build multi-regression model against this data set. What are the general approaches to test the interactions of these ...
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### Why do the residuals from a factor analysis have mean zero?

The model is given below: \begin{align} y_1 - \mu_1 &= \lambda_{11}f_1 + \lambda_{12}f_2 + \dots + \lambda_{1m}f_m + \epsilon_1 \\ y_2 - \mu_2 &= \lambda_{21}f_1 + \lambda_{22}f_2 + \dots + ...
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### Given a chi-squared distribution, find $\Pr(Y \in \mu \pm 2\sigma)$

Given a chi-squared distribution of df = 8, which R command do I use in order to find $P(Y \in [\mu \pm 2\sigma])$? That is, the probability that $Y$ lies within 2 standard deviations of its mean? I ...
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### Log probability vs product of probabilities

According to this wikipedia article, one can represent the product of probabilities x⋅y as -log(x) - log(y) making the ...
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### Wishart distribution in BUGS with prior on the scale matrix

I am attempting to sample from a wishart in WinBUGS where the scale matrix has priors on the entries. dwish() in WinBUGS won't allow this, so I am attempting to ...
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### Discriminant validity testing

I am required to assess the discriminant validity of the constructs in my model. I have used the Fornell and Larcker (1982) method, however I now need to explore discriminant validity using the ...
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### How to define samples in caret package?

I am using the caret package and need to train a random forest, where only certain samples should be in the held-out set. I want to define the sampling for each tree in the random forest, for say 100 ...
16 views

### Statistic confidence interval

I have this statement: If a 95% confidence interval for the mean was computed as (25,50), then if several more samples were taken with the same sample size, then 95% of them would have a ...
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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 ...
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### 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 $u_i,u_j$ $\in \mathcal{R}^d$ ...
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 ...