# All Questions

4 views

### Which model of lm/lme to believe?

I have a data set of height values for several individuals of several species in 2 different conditions. Not all the species are found in the 2 conditions. I want to compare height values between ...
3 views

### How to loop through elements in a large list, make NA variables for holes in data, and create new variable in another dataframe in R?

I am trying to find a way to avoid writing 78 lines of code by using some sort of loop in R. Say I have the following: ...
15 views

### Caclulating probabilty of drawing vector from multivariate normal distribution in R

given vector of mean $\mu$ and covariance matrix $\sigma$ as parameters of multivariate normal distribution, how can I calculate the probability of drawing $k$-dimensional vector from that ...
4 views

### Compute TFIDF matrix based on another TFIDF matrix using R 'tm' package

Using the R package tm, I'd like to compute a TFIDF matrix (tfidf_matrix_b) based on a previously computed TFIDF matrix (...
5 views

### Confidence interval on point biserial correlation coefficient

How can I calculate the confidence of a point biserial correlation coefficient? I'm calculating the point biserial correlation between a continues variable (score on a test), and a dichotomous ...
5 views

### Linear Mixed Effects

I am looking for seasonal influence on how effective a herbicide treatment is. I have data over ten years of several polygons that have received the treatment multiple times at varying intervals. ...
12 views

### Where can I find a data set of US Individuals? [on hold]

I'm looking for a data set of US citizens/residents, etc. With data on things such as age, geographic location, gender, income, marital status, etc. The more the better. Where can I find an ...
7 views

### Classification in real time without prior knowledge of the number of classes

Is there an implemented algorithm (with python/R or java in preference) that can classify incoming data from an unknown generator with absolutely no prior knowledge or assumption.
18 views

### Help logistic regression [on hold]

I have to predict a binary variable with logistic regression. The idea is to classify a number of subjects each either sick or not sick. Therefore, I have 11 risk factories for each person and have to ...
10 views

### Lmer v. lm with Dummy Variables. Where Does the Math Differ in a Simple Example?

I am trying to understand the concept of mixed effect along with the R syntax in lme4 with simple scenarios out of the dataset ...
8 views

### Which statistical test should i perform find performance diffecence in two sample?

I am trying to find if there is any deference in performance withing two groups of sample. ...
6 views

### Single-factor random effect ANOVA and components of variance

I've needed to learn some DOE for work and I've been going through Montgomery's book using R to help with the calculations. The fixed-effect models have been straightforward, but I have some trouble ...
8 views

### Multinomial Logistic Question

Using PROC Logistic with the glogit link, I am attempting to classify records according to 1 of 3 responses (0, 1-2, 3+). After cleaning and running multiple models, I landed on what I thought was a ...
10 views

### Which normalization procedure is suitable for Principal Component Analysis (PCA)?

I have a data-set that has features with different ranges, scales and measurement units so as proposed in literature I'm using Principal Component Analysis (PCA) with "correlation matrix". In this ...
14 views

### Interpretation of Saturated Model vs. Model with Interaction and One Main Effect

Say that I have two regressions: 1) $Y_i = \alpha_0 + \alpha_1 X_i + \alpha_2 X_i*Z_i + \epsilon_i$ 2) $Y_i = \beta_0 + \beta_1 X_i + \beta_2 Z_i + \beta_3 X_i*Z_i + \epsilon_i$ $X_i$ and $Z_i$ are ...
5 views

### Fitted Confidence Intervals Forecast Function R

I am using the forecast function in R written by Rob Hyndman. I am trying to determine the best way to determine confidence intervals for the historical fitted values. I would like to plot how often ...
9 views

### All of the series used in a model must be stationary at the same order of differencing

While practicing VAR analysis, all of the series used in the model must be stationary at the same order of differencing. Is this correct? For example, let $X$~$I(1)$ and $Y$~$I(2)$. Can I use these ...
11 views

### Factoring Fourth degree polynomial for invertible ARMA process

I have to represent a $MA(4)$ process as an $AR(\infty)$. In this regard, I need to factorize the polynomial $(1-\theta_1L-\theta_2L^2-\theta_3L^3-\theta_4L^4)$ to have a representation $(1-z)^{-1}$. ...
5 views

### model selection in quantile regression

I am quite new in quantile regression, and I am using it in R (quantreg). I have around 17 predictors,and I would like to select the best subset of predictors. Then, I was wondering if it would be OK, ...
7 views

### On choosing the size of test set for an (already collected) dataset

When I search online for criteria to select the fraction of a dataset that should be set aside as test set, invariably the answer boils down to "it depends" (on the type of data, the type of study, ...
3 views

### Caret - Changing tuneGrid gives different results for same parameters

I'm having an issue training a GBM model in caret. I'm quite new to all of this, but I'll try to explain things as best as possible, but please let me know if you need any further info. My code looks ...
9 views

### Abstraction in neural networks

Without running through all possible scenarios, can a neural network learn that 4 or more dots in a row, anywhere, is a line? I've been looking for an existing method, however "abstract" comes up in ...
25 views

### What is the duality relationship between eigensystems of X X' vs X' X?

I want to know the relationship between the eigensystems of two non-negative-definite (covariance-like) matrices. Both are derived from X which is a T-by-K real matrix (wlog say K > T). I avoid ...
6 views

### Filtering to avoid the Slutsky-Yule effect in a moving window average?

Can anyone suggest a generally accepted method of filtering time series data to avoid the appearance of artifactual oscillations when smoothing the data using a moving window average? Is it simply a ...
23 views

### Daily data, different dates

I have downloaded two different daily data sets, both for the same period. Together I want to use them to construct data for another variable. However, the problem is that the dates do not exactly ...
12 views

### How to Schedule R Activity [on hold]

I am having following requirement, 1. Run R regression techniques on mainframe Data 2. Do visualization and save it for business users My questions are, What is the best way to integrate R with ...
5 views

### Training an Elman Recurrent Neural Network?

I have few doubts related to training Elman RNN using Backpropagation Through Time Algorithm. Assume, I present a sequence to the network and the network adapts the parameters based on the error ...
10 views

### Metropolis : Set first sample value instead of randomly generate an arbitary value

According to Metropolis-Hasting algorithm, the first sample is an arbitrary value generated randomly at the Initialization step. ( http://en.wikipedia.org/wiki/Metropolis%E2%80%93Hastings_algorithm ) ...
17 views

### What are some standard bimodal distributions?

I have plotted this curve using the default kernel density estimate function in R I am looking for some standard distribution which could be close to this. Is there any standard bimodal distribution ...
8 views

### Does VECM use the stationary series or the originals ones?

I have some cointegrated series and I decided to build a VECM model. (I differentiated them twice in order to get stationary series and that led me to believe that they might be cointegrated - I ...