# All Questions

2 views

### Combining different metrics to calculate composite score

Let's assume I have 3 metrics to evaluate a student. 1)Test Marks (0-50) 2)Weight of the student (KGs) 3)% Attendance (0%-100%) I want to calculate a total composite score which is a function of ...
2 views

### fixed-effect nested factors in R with only SOME combinations present

I have a large data wth numerical response and two categorical factors: date and site. There are about 350 dates and 25 sites, but not all sites have observations on every single date (most have only ...
3 views

### Confused about cross validation for model stacking

I'm reading section 8.8 of Elements of Statistical Learning, and though I keep reading the section on calculating the ensemble weights I'm missing something. It says that the stacking weights are ...
7 views

### Model failed to converge

I'm doing a variable selection for the interaction gender:type2 now ...
13 views

### What are parametric models?

The term Parametric Models does not sound unfamiliar to me, but I do not exactly know what they are. Can you please briefly explain what model is parametric and ...
7 views

### Weibull Mixture question

Is it possible that a mixture of Weibull RVs is also Weibull distributed, and if yes, what are the necessary conditions?
6 views

### Recommendation: Fast algorithm for logistic random effects?

What is the fastest algorithm for fitting a simple logistic 'random effects' type model, with only one level of categorical predictors? Another way of putting it might be a logistic regression with ...
7 views

### Correcting data for mean but also variance

My data: I have data that range from 0 to 2 for numerous individuals. The scores are more or less normally distributed and vary continuously, but the scores are always between 0 at the minimum and 2 ...
8 views

### Probability-generating function of two independent Poisson random variables

Let $X_1, X_2$ be two independent Poisson random variables with mean $\lambda_1, \lambda_2$, and $S_2 = a_1 X_1+a_2 X_2$, where the $a_1$ and $a_2$ are constants. Is it correct, that ...
10 views

### Linear mixed models

I have some spatial measurement for two quantities, x and y. y is my dependent variable that I am looking to build a linear mixed effects model.Each point in space (lat,long) has one value of x, for ...
4 views

### Classification Algorithms

Rather than due a google search and hope to find "the best" or an exhaustive list of classification algorithms I thought it might be easier to pose my questions here, and then get advice from you ...
6 views

R noobie here. I'm am trying to use a package that I download off of github using source_gist, but it appears that I need to re-download it every time I quit R ...
16 views

### Curvilinear relationship with moderator

I am trying to moderate a curve and determine which equation I should follow. A simple curvilinear relationship has the following equation: (1) $Y = b_0 + b_1X + b_2X^2$ (i.e. a linear term and a ...
15 views

### What to do after running an explorative factor analysis?

Say I asked 1000 people to evaluate 10 items about one product. The data looks like ID item1 item2 …item10 1 2 3….. After running an explorative factor ...
14 views

### Determining probability mass function (PMF) using Bayesian approach

For instance, a person is trying to determine the light intensity (unit: Candela) from a source that he knows must be coming from one of the 3 mediums (A, B, and C). From his experience he have ...
7 views

### Characterize this discrete distribution [on hold]

Suppose we have $k$ buckets, with an infinite number of balls in each bucket. We assign to bucket $i$ a probability $p_i$ (so that $\sum_{i=1}^k p_i=1$). If we draw a ball from one of these buckets ...
12 views

### Multiple Regression - Converting Standardized Coefficients to Unstandardized

I recently performed a multiple linear regression using a standardized set of data, and I was wondering if it possible to convert the standardized coefficients from the regression into usable ...
11 views

### Ordinal variable with 'don't know'

Can a variable that contains 'don't know' as a response be ordinal? For example, say the variable corresponds to responses to the question 'Do you agree with ...?' where the responses are: Agree ...
12 views

### Paired T test vs 2 sample t test

I have been given data that includes 20 different households and what each household spends on grocery and restaurant. I need to run a t test and I'm not sure if I should use a paired t test or a 2 ...
6 views

### Need help with calculating this problem not sure where to start

To determine the main cost of groceries in the area an identical grocery cart of food is purchases at a random sample of 20 stores. The 20 grocery totals before tax are recorded and a 95% interval for ...
33 views

### What is the relation of p-values and type 1 error?

In hypothesis testing we set an accepted level of type 1 error probability $\alpha$ and observe whether a sample statistic is equally likely or less likely to be observed if the null hypothesis was ...
16 views

### What is the derivative of a matrix with respect to f? The matrix has softmax function in it

I need the derivative of W, which has the following expression. W is matrix which contains entries from softmax function. I couldn't find the derivative.
5 views

### Sample size in the Latin Hypercube simulation to calculate P90, average and P10 and number of variables relation

I am preparing some simulations to determine the P90, average and P10 of a parameter. How many runs do I need to have to get a reliable answer (let's say 5% margin of error and 95% confidence)? It ...
11 views

### Sample Mean and Sample Standard Deviation [on hold]

How do I calculate sample mean from the question like below: A company has following samples of leaking goods with gaps 0.290, 0.104, 0.207, 0.145, 0.104,0.124. I couldn't understand the question ...
8 views

### Recaculating control limits when an out of control situation is displayed

When plotting control charts if a point plots outside the control limits then the reason for that point to plot outside is checked and if an assignable cause is found to be the cause then after ...
12 views

### Imputing using CFA for use in a Cox regression

I am using CFA (confirmatory factor analysis) to create a measurement model of social capital that is to be used in a Cox regression. Because of missing data I first impute the incomplete data by MICE ...
9 views

### Moderating a curve [on hold]

I have a paper that has a main relationship with a negative curve. It actually looks like a left leaning hockey stick. We have three moderators - two that strengthen the negative slope and one that ...
6 views

### How to test composite hypothesis for the linear regression model

I want to test $H_0:\beta_1>0,\beta_2=\beta_3=0$ in the model $Y = \beta_1x_1 +\beta_2x_2 + \beta_3x_3+\epsilon$. How can I do this?
13 views

### Grid search error in LIBSVM while optimizing C and g parameters

I am using libsvm for a one-class classification problem. I am trying to select the ideal C and gamma parameters for different kernels(polynomial, linear and rbf) I am using the suggested matlab code ...
37 views

### What coefficients do I use for a binomial distribution problem?

I'm studying for an exam and my study guide explained combinations, permutations, and binomial distributions, but didn't cover much how to recognize where each comes into play in problems. I'm having ...
15 views

### What are the various basic kernels available?

I am currently following the book Gaussian Processes for Machine Learning by C.E. Rasmussen and C.K.I. Williams and I have come across various kernels in their Chapter 4 I have also gone through the ...
23 views

### Why does NSDIFFS (R forecast package) never show seasonality? [migrated]

I've been using the EViews statconn DCOM interface to loop a large number of series from FRED through the nsdiffs(test=c("ch")) function in the forecast package of R to examine what percent of them ...
10 views

### What are the parameters of a Wishart-Wishart posterior?

When infering the precision matrix $\boldsymbol{\Lambda}$ of a normal distribution used to generate $N$ D-dimensional vectors $\mathbf{x_1},..,\mathbf{x_N}$ \begin{align} \mathbf{x_i} &\sim ...
28 views

### Is high AIC a bad feature of the model?

I have a model with AIC equal to 78 809. Does this mean this is a very bad model or the intepretation should be different? There are 15 variables, 2-level response variable and 40 000 rows. ...
20 views

### Simulating a data generating process

Suppose I wanted to simulate the data generating process of a non-linear regression with ma(1) errors. So, without going into many unnecessary details, the model is y_t = f(x_t,x_t-1,..., x_{t_0}, ...
81 views

### Linear independence vs statistical independence (PCA and ICA)

I'm reading this interesting paper on application of ICA to gene expression data. The authors write: [T]here is no requirement for PCA components to be statistically independent. That is true, ...
16 views

### How to standardize text data for training Neural Networks?

I want to train neural network with text data(natural language) as input for classification purpose. One way for standardizing text data for neural network is to use N-GRAM/SKIP-GRAM representation ...
7 views

### How to plot ROC curve after using SMO classifier in weka? [on hold]

I classified my data using SMO function in weka. The ROC plot that I got is not a curve (it is based on just one threshold). can anyone help me to plot ROC curve for more decision threshold? how can ...
16 views

### 2 factor factorial model with random factors

Using lme4, how does one define a full 2-factor factorial model with both factors (and their interaction) being random? Specifically I am trying to recreate the ...
9 views

### Regarding post pruning in decision tree

Just 2 issues: 1) what should we do say for example we get 5 Yes and 2 No for a single final leaf node attribute? 2) How to post prune using Chi square test?
4 views

### Multi-signal coherence test

Is there an accepted measure for multi-signal coherence? The signals are time-domain EEG voltage readings from various parts of the scalp. I was working with magnitude-squared coherence, but it only ...
5 views

### Anyone knows how to make a LSTM layer that is able to be trained with arbitrary BPTT time steps and easy to be stacked together?

Anyone knows how to make a LSTM layer that is able to be trained with arbitrary BPTT time steps and easy to be stacked together? I am now implementing a basic version of LSTM layer. My scan function ...
17 views

### How can we compute cumulative change rates for time series data?

Take the annual precipitation data for some area from 1960 to 2008 as an example. How can we compute cumulative change rates for such data?
31 views

### Is there a correlation index for Binary Variable vs Quantitative variable?

I know that I can use a logistic regression model to test if quantitative variables influence the binary variable, but I would like to have an Index, like Pearson correlation index to tell how strong ...
39 views

### Product of two gaussian processes

Given, $\ {y}_{i} = N({\mu}_{i}, {\Sigma }_{i})$ If we go by the link http://www.tina-vision.net/docs/memos/2003-003.pdf then we can understand that the product of many multivariate gaussians can ...
6 views

### Is there a general structure for papers/documents explaining computer vision databases?

I recently created a database of images for testing a specific computer vision problem. Due to lack of data in the first place, I designed an algorithm which generates new images from the few existing ...
7 views

### Applicability of Hilbert-Huang Transform for linear trend analysis

I have a question about the applicability of the Hilbert-Huang Transform / empirical mode decomposition (HHT/EMD). Suppose I have a time series dataset in which there is probably an N-year periodic ...
23 views

### Rearrange regression equation that includes a dummy variable

This is my regression equation: $10 = 5.44 + 0.26X_1 - 3.19X_2$ $X_2$ is a dummy predictor with two levels. Assume that the value of $X_2$ is 1 therefore regression equation is: \$10 = 5.44 + ...