# All Questions

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### Normal Distribution Qn

Given X~N(20, 16), find a) the value of k such that P(x < k) = 0.2758 b) the value of k such that P(x > k) = 0.1539 How do I solve this?
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### Changing the sequence of variables in a random forest model changes the classification accuracy

I find that the classification accuracy of the random forest model changes when the sequence of the input variables change. E.g. ...
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### Understanding QR Decomposition

I've got a worked example (in R), that I'm trying to understand further. I'm using Limma to create a linear model and I'm trying to understand what's happening step by step in the fold change ...
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### Bootstrapping a t statistic - Rationale and procedure

I was hoping someone could help me out with this. I've seen similar questions on the forum, but I need to know if I've understood the correct rationale and procedure for bootstrapping for my ...
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### How do I solve the following task?

I came across this task that I have no idea how to solve, because I'm not very good at statistics, so I was wondering if someone could help me understand it. 7 scientists with very different ...
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### Testing for unit roots

I am an absolute beginner and I need help on testing for unit-roots in Stata. As the data is unbalanced (no missing values, but some time series begin later than others) it seems to me that I could ...
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### How to calculate probability of observing a value given a permutation distribution?

I have a single observation with value $x = 0.5$ that comes out from a complicated computational process. I would like to know what is the probability to observe such value by chance. To attempt to ...
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### Are fixed bias neurons or biased neurons better?

When building an artificial neural network, there seems to be two differing philosophies in usage of biases. There are those groups that propose neural networks with a fixed bias neuron with a ...
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### 2sls for panel data in R

My question is how to do 2sls estimation for panel data (fixed effects) in R software? I try to use ivreg but I cannot set fixed effects option there. Any suggestion would be good!
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### Is it fair to say that most real-life distributions have finite variance?

In most real scenarios I know the random variable X isn't unbounded.
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### Concepts of Exploratory Factor Analysis

As a conceptual question, In Exploratory Factor Analysis, How a factor created?! I like to know, What is your simple answer to this question. Imagine, My academic field does not dependent to ...
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### Bayesian Regression Full conditional distribution

I have a problem with the derivation of the full conditional distribution of the regression coefficients in a simple bayesian regression. The source of the following equations is: Lynch (2007). ...
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### Richness presence bacteria

I need to find the richness, dominance and diversity about the presence of a bacterial population in different treatments. Is possible to make the calculation about the richness, dominance and ...
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### Test for proportions - which one to choose?

I have a general question regarding proportions. Let's say, for simplification of things, that I have 2 groups of subjects (treatment and control), and for each subject I measure success or failure (0 ...
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### Maximizing log-likelihood in R

I am trying to perform ML estimation for a continuous distribution given by \begin{align} F(x;\Phi)=\left(1-e^{-\eta^{k}(x)}\right)\left(1+\lambda e^{-\eta^{k}(x)}\right), \quad x > ...
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### How to determine trend in rainfall data?

I have annual average rainfall data in mm/day units. I want to see the trend of the rainfall, whether its increasing or decreasing. How to do this. My teacher told to put a linear regression line and ...
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### How can we construct cumulative meta analysis plot after doing proportion meta analysis

Need to do cumulative plot for proportion meta analysis. Suggest software
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### Meta regression in proportion meta analysis

I completed proportion meta analysis using stuart-ord method. Now need to do meta regression. I used stats direct for proportion meta analysis. Previously I did meta regression using comprehensive ...
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### Alternatives to Chi-Squared for Single Categorical Outcome and Single Categorical Predictor w/counts for factors [R]

I am from an applied background, where X2 and G-tests are the default ways to analyze count data (default as in, until today, I had no idea there were other ways, as I was only taught these methods). ...
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### Exponential, Gamma or Weibull Distribution used to represent deterioration rate in inventory models? [on hold]

Would you please give a comparison of these distributions, used for other variable, say, rate of deterioration (decay) of items? Also refer: Weibull Distribution v/s Gamma Distribution
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### Choice of base distribution for Dirichlet Process Mixture Model when data is categorical

While calculating a Dirichlet Process Mixture Model on a data set that has discrete/categorical attributes, what kind of base distribution would you assume? When the data set is completely numerical, ...
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### Standard error computed by MATLAB multcompare?

Here is my toy data y = [1; 1; 2; 6; 7; 3]; and their group information is as follows grp = ['a'; 'b'; 'b'; 'a'; 'c'; 'c']; ...
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### Minitab: Variance/standard deviation calculator problem [on hold]

I have a small problem with the calculator in Minitab. The question is shown in the picture, and the highlighted is the portion that I am having problems with. Now, this is how it looks when I ...
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### Softmax Regression GD Update Derivation

I'm implementing softmax regression and am deriving the max-log-likelihood update for gradient descent by hand first. Coming from the Stanford UFLDL site, they show the gradient of the cost function ...
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### AMOS: How to get estimates for two models combined to calculate AVE and CR for whole sample

I am wanting to report the AVE and CR values for two groups individually and then both groups together. I am using Amos to find the standardized regrettion weight and I understand how to do this for ...
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### How to incorporate characteristics of the object of outcome variables as predictors in model

I'm working with survey data for a social science research topic. The particulars aren't super important, so I'll use a simplified version to make it easier to understand what I'm trying to do. I say ...
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### Capture recapture model validation

In the absence of an actual population to test on, what are the best practices for validating capture recapture models?
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### hard statistics question [on hold]

A sample of size n=19 is selected from a population with mean 50. After a treatment is administered to the individuals in the sample, the mean is found to be M = 55 and the variance 64. Are the data ...
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### how to interpret metrics for my model

I understand how these metrics are determined but can anyone give me typical poor, acceptable, good, and outstanding values RAE and RSE?
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### Test cases for HMM implementation

I've written some simple code to fit Hidden Markov Models with discrete emission probabilities (similar to this implementation, which follows Rabiner's tutorial very closely). I'd like to extend my ...
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### How to do one-vs-one classification for logistic regression?

I have a dataset with 4 clases and I want to apply logistic regression with one-vs-one classification. So, first I train for each pair of classes a logistic regression classifier (i.e. calculate the ...
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### Given the same before-after differences within groups, is it relevant whether time trajectories converge or diverge?

Both drugs are associated with the same decreases in mean blood pressure in both scenarios. Given that we attach the same meaning to any blood pressure decrease of the same amount, does scenario B ...
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In my experiment, I diluted a chemical in water and recorded its Raman spectra. Then I repeated this with different concentrations. As I can clearly see some peaks decreasing in intensity when I ...
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### Time dependence and cumulative logit regression question

I'm looking to do some research with the GSS (the General Social Survey; a survey that asks over a 1000 people every year various questions and collects their demographic information as well). I'd ...
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### Using lmer for repeated-measures and RCBD

I am trying to figure out the best way to model the error using lmer for a randomized complete block design (RDBC) where we measured soil nitrogen weekly for 2 years. There are: 4 Blocks (A, B, C, D) ...
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I have been trying to fit Adaboost to work with continuous valued data set and the more I read the more I keep getting confused. I have read about the multiclass Adaboost with log(K-1) addition to ...
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### How to train lstm layer of deep-network

I'm using a lstm and feed-forward network to classify text. I convert the text into one-hot vectors and feed each into the lstm so I can summarise it as a single representation. Then I feed it to the ...
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### I would like to know exactly WHY NN inputs have to be within -1 and 1

My questions is similar to this other question but I want to know exactly why the inputs have (or is strongly recommended) to be within this range. I know computers can deal with numbers within a ...
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### How do I interpret and report the output of a logistic regression in R on data that are all binary (0,1)?

My minimum adequate model is shown below. My independent variables (e.g. One, Five) represent habitat categories for which species have either been designated to (i.e. the assessment found that they ...
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### Distances between successive points - Statistical Test

I have a set of experimental data which comprises distances between successive points: I also have a set of similar data that has been generated by a model that attempts to recapture the ...
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### Basic Parking Probability question

how would you solve the following problem ? Parking spaces at a business school are arranged by a random monthly lottery. there are 3 spaces for every 10 students who want one and all of them have an ...
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### Why does GEE produce the same parameter estimates as OLS?

The quasi-likelihood function optimized under GEE is: $S_k(\beta)=\sum_{i=1}^{K}\frac{\partial\mu_i}{\partial\beta_k}\nu_i^{-1}(y_i-\mu_i)=0,$ where $\mu_i=h(\textbf{x}_i,\beta)$ is the conditional ...
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### R - Variation of “How to plot decision boundary of a k-nearest neighbor classifier”

This is a question related to How to plot decision boundary of a k-nearest neighbor classifier from Elements of Statistical Learning? I've been playing with that example, and would like to try to ...
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### What is the best way to learn hadoop [on hold]

I would like to learn hadoop. I know a bit of linux and sql. What would be the best way, handson training or online videos or anything else. My assumption is since I don't have the hardware required, ...
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### How to train a svm classifier with a linear and rbf kernel? [on hold]

I have a image database of size 2000 , each of which is converted into feature vector of size 1024. Similarly there is another test dataset of size 2000 for testing purpose. I would like to see the ...
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### How can you detect outliers in a group of face images?

I'm trying to filter an image database which contains some irrelevant pictures. All the faces are labeled with points around the face contour, eyes, mouth, eyebrows, have age and gender. The faces are ...
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### Sample size calculation, linear regression

I have just had my viva and my sample size calculation was criticised as it was based on r2. I was told to base the sample size on the minimal magnitude of association. My outcome variable is HbA1c, a ...
There are two independent uniform continuous random variables $X$ and $Y$ (such that $0 \leq X \leq 10$, $0 \leq Y \leq 10$). The function $f$ is the difference between the two random variables ...