# All Questions

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### How exactly is sparse PCA better than PCA?

I learnt about PCA a few lectures ago in class and by digging more about this fascinating concept, I got to know about sparse PCA. I wanted to ask, if I'm not wrong this is what sparse PCA is: In ...
9 views

### Statistical Problem

A psychiatrist hires you to study whether her clients self-disclosed more while sitting in an easy chair or lying down on a couch. All clients had previously agreed to allow the sessions to be ...
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### Statistical problem / explanation

A researcher studied the effect of television violence on concentration of a particular blood chemical. In this study, 40 participants were measured over a period of an hour prior to watching a ...
7 views

### Calculating Second-Order Tikhonov Regularization Parameter in Mathematica

I am trying to map slowness of underwater sound velocity in a river using some tomographic device. The location of each acoustic receiver/transmitter is shown in the picture below To find the ...
10 views

### Predicting data based on two data sets

I'm brand new to SAS programming, and I'm having difficulty figuring out this issue: I have two sets of data 1st set has 4 columns (income is a continous range of numbers, sex is 0 for male - 1 for ...
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### Time Series Forecasts of Appointments with Pre-Reqistration

Looking for some tips and ideas. I get a list every day of the number of appointments for each day for the next two weeks for a clinic. I have quite good history of these list, and the actual number ...
13 views

### Comparing linear regression models created from different data sets

I have one linear regression model [Mold] created from 12 points where I can calculate a single value of RMSE between the predicted values and the actual observed values. This model is then used to ...
14 views

### On the application of an algorithm for classification

Given, a set of training pattern p_1 = [1 -1 -1 -1 -1 1 -1 1 1 1 1 -1 -1 1 1 1 1 -1 -1 1 1 1 1 -1 1 -1 -1 -1 -1 1]'; I can calculate the weight by $W = p_1*p_1'$ ...
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### How many different random initializations should I perform with Lloyd's algorithm to obtain the optimal clustering with X% of confidence?

I use Lloyd's algorithm for clustering. Since it relies on a random initialization and Lloyd's algorithm can get stuck in local optima of the k-means objective function, I have to run it several ...
21 views

### How to determine if % selecting Option A is statistically different from selecting Option B in a survey?

I ran a survey on pricing and asked respondents to choose between option A or Option B. 61% chose option A and 39% chose Option B. The sample size is 90. How do I determine if the % selection Option A ...
8 views

### How much do self organising maps suffer from local minima problems?

How much do self organising maps suffer from local minima problems? I assume that the original orientation of the grid can have major orientation on the resulting shape of the grid, but does this have ...
26 views

### Term is significant linearly, quadratically and in interaction?

I used deletion tests to identify ecological factors that relate to the number of parasites on rodents. There is one factor that is significant linearly, quadratically and in interaction. However, the ...
9 views

### Finding subsets with Branch-and-bound techniques

Hello I am trying to find a Matlab version of a function which performs best subset selection for least squares regression using leaps and bounds (branch and bound) approach. Like in the paper by ...
16 views

### Using caret train function to perform lm with 10 repeated 10-fold cross validation

I'm using the caret package at the moment to perform different forms of analysis on my dataset. I did the following to do 10-fold cross validation, 10 times:- ...
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### Comparison of Kaplan-Meier curves across ordered groups

I am familiar with the log-rank test for comparing multiple Kaplan-Meier curves, but I am looking for a test that will compare across ordered groups (an ordinal variable). A significant result from ...
31 views

### What is the actual equation of the standard 68/95/99 bell curve graph? [duplicate]

I want to connect Calc with Stats via cumulative density and taking the area under the curve. However, what is the equation of the curve that models the standard 68/95/99 bell curve?
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### Coefficients from a penalized Cox PH

I'm using the R package Penalized (0.9-42) on a Cox PH model. I'm using L2 (Ridge) on the grounds that I don't want to shrink my coefficients to 0. I don't understand why when I ask for: ...
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### computing confidence interval for ranges, confidence level 0.95

I have some ranges of values and frequencies of each range. Participants choosed an entire range when asked, and not a particular value. Example: Range [0,20] : frequency = 20 Range (20,60], ...
56 views

### Best modelling packages in R?

In R I use a lot the packages plyr, stringr, Hmisc and ggplot2. Each of these packages take the base code and make functions that are more intuitive and easier to work with. Each of these packages ...
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### Absolute vs. Relative Difference in Survival Time - Is this possible?

So there's a fairly well characterized difference between relative risk and absolute risk for conventional cohort studies, and for many questions, the absolute risk is arguably more appropriate. Is ...
15 views

### Why is the scatter diagram always symmetric around the SD line?

This may seem like a dumb/vague question. When you draw a line of slope $\frac{\sigma_y}{\sigma_x}$, why is this line the major axis of the scatter-diagram ellipse? Is this some property of the ...
26 views

### Calculating confidence intervall for quantiles first by hand (than in R)

It would be great if someone can check whether my approach is correct or not. Question in short will be, if the error calculation is the correct way. lets assume i have the following data. ...
23 views

### Meta-analysis with a binary response variable

I am attempting to fit a model to my data for meta-analysis I'm working on. The response is binary (0 or 1), and I want to specify a binomial distribution with logit link function. The 2-3 (depending ...
27 views

### Poorness of Kernel methods on visual pattern recegnition?

I am currently reading the recent papers mainly written by Y. Bengio [1],[2],[3]. There are very strong claims about poorness of Kernel methods on recognizing handwritings in many general cases but ...
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### Repeated measures mixed multinomial model in R - extract coefficients

I would like to perform repeated measures mixed multinomial model using R. To be exact I would like to do MaxDiff analysis similar to SawTooth Hierarchical Bayes method. I want to use mixed models ...
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### Estimating distribution from censored data

$X$ is a positive variable with known support (assume discrete support, if that simplifies solution). $Y$ is another variable with the same support. $X$ and $Y$ are independent. $Z$ is equal to $X$ ...
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### I have a problem in bayesian networks get p(E|A)

I'm doing this book "Modeling and reasoning with Bayesian Networks" and I have this problem: ...
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### Guess several distribution's parameters from a list of interarrivals

Just a small introduction to the setting: I have traffic that is generated using several layers. Layer 3 consists of the basic packets, while Layer 2 is a more high level grouping of packets, and ...
20 views

### Expectation of correlated variables

I'm looking to compare effects $\delta = \frac{\mu_T - \mu_C}{\sigma}$ for two studies, compared with the same control group. In order to find the covariance of effects for treatment A and treatment ...
22 views

### Conditional Logistic Regression, Rare Events and R

I have a panel data set organized around 35 provincial units, with 110 binary "positive" outcomes in the dependent variable. This is for about 2600 observations in that data set. I have a couple ...
26 views

### review papers on P-values, adjusted P-values and common statistical tests in bioinformatics

I'm looking for review papers which give comprehensive reviews of P-values, adjusted P-values and common statistical tests in bioinformatics.
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### Goodness of fit test for a normal distribution

In the example from the web site I was trying out this problem in page 107 about Goodness of fit test for a normal distribution.Question is about analysis of fat content of hambergers. I understand ...
37 views

### Bootstrapping in R using the boot {boot} and Boot {car}

I'm trying my hand at resampling techniques with a dataset I have, and I think either I'm missing a conceptual point with bootstrapping, or I'm doing something incorrectly in R. Basically, I'm trying ...
27 views

### How to Reduce Error Term

My question is "What could you do if you wanted to reduce the error term (e)? I know the error term is basically the distance between the line and the point but I don't know how you would reduce it. ...
31 views

### Hamiltonian Monte Carlo: why is reparameterizing needed?

In the Stan user's manual (Version 2.0.1, page 157), it says A hierarchical model such as the above will suffer from the same kind of inefficiencies... [for a Hamiltonian Monte Carlo method] ...
15 views

### Goodness of Fit Test for Logistic Regression with small n_i

I would like to test how well my model fits the data. The response is binary and the Chi-Squared Test cannot be applied for the residual deviance because the $n_i$ are $1$. To use the Chi-Squared GOF ...
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### Help fitting a poisson glmer (getting an error message) [migrated]

I am trying to fit a Poisson glmer model in R, to determine if 4 experimental treatments affected the rate at which plants developed new branches over time. New branches were counted after 35, 70 ...
17 views

### Validity Index Pseudo F for K-Means Clustering

The Validity Index "Pseudo F" is described as: (between-cluster-sum-of-squares / (c-1)) / (within-cluster-sum-of-squares / (n-c)) with c beeing the number of clusters and n beeing the number of ...
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### What are some examples of real-world processes that are well-described by AR, MA, ARMA, or ARIMA?

Subject says it all - AR/MA/ARMA/ARIMA are often described as workhorses of time series analysis. But what are some real-world examples where these methods gave great results, and another more modern ...
13 views

### Model selection between exponential and gamma distribution using cross validation

I have fitted the exponential and gamma model to my univariate data and obtained the MLE estimates using the R package "fitdistr", now I'm trying to do model selection based on leave-one-out cross ...
21 views

### Different outputs for weka and Excel - linear regression

I was double-checking my regression outputs from weka and Excel. All coefficients are the same, however I get a considerably different intercept. How come? Also, is it possible to run a t- or p-test ...
14 views

### AIC and BIC for Support Vector Machine inside e1071

After training a support using the e1071 package of R, how can I calculate an information criterion such as AIC or BIC?
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### Missing input value during prediction of a generalized linear model

If I'm doing prediction with a generalized linear model and a new batch of inputs comes with some missing values, what strategies can I use to minimize the loss of information from the missing inputs? ...
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### Generating null distributions by a residual permutation procedure

I am trying to understand the method described in this paper which describes an hypothesis-testing framework for stable isotope ratios. The data are in a bivariate isotopic space and the metrics that ...
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### nonparametric MARS regression

Most statistical methods assume homogeneous (outlier-free) data in which all data points satisfy the same model. However, real data are (not) NEVER homogeneous; and accurate identification of outliers ...
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### Spatial interpolation in program R [migrated]

I'm having some trouble with spatial interpolation in R. I need to create an interpolated surface of a count variable across the area of a polygon. I can create this output in ArcGIS, but would like ...
30 views

### Using PC scores in PCA

This might be a basic question, but I am analysing the diversity of floral traits in plant communities. Some of my data are reflectance spectra. I want to reduce the complexity of these data by doing ...

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