# All Questions

2k views

### How to reduce the number of variables in cluster analysis?

I've got 10 (yes, only 10) cases over 1000 variables (e.g. measurements of concentrations of 1000 different compounds at 10 different time points). I can group these cases into 3 clusters in ...
3k views

### What to use, k-means or hierarchical clustering for presence absence data?

I am currently working with a presence-absence database that is mostly zeros (~5% are ones) representing species in space (a species per site matrix). I would like to explore the spatial pattern of ...
784 views

### For linear regression, what's the distribution of error term from Classical and Bayesian point of views?

I know that linear regression is based on the assumption that the errors are normally distributed (from both bayesian and classical views). I'm just trying to verify this assumption based on the final ...
312 views

### Why is an odds ratio less than the lower limit of 95% confidence interval?

Can there be a situation where odds ratio is less than the lower limit of 95% confidence interval? If so, what could be the possible reason for this? The formula I used to calculate confidence ...
606 views

### Which are the most effective clustering ensembles?

In supervised learning, there are some ensemble methods that overcome others significantly (adaboost or random forests to mention some). Few years later, also ensembles in unsupervised learning were ...
653 views

### Testing if a proportion is different between groups

I have data on the status of a treatment in approx 800 hospitals. For example: ...
149 views

### Seeking for a fast non parametic clustering algorithm

I'm looking for a fast clustering method to cluster a large kind of datas to a unknown count of clusters. I know about the PAM-Algorithm. But it's only efficient for low datasets. Is there a ...
803 views

### Survival Analysis with Multiple Events

Suppose we have a population $P$ that we are interested in. We want to track the onset of particular conditions (i.e. $A$, $B$ and $C$). Suppose that as blood pressure drops, these events occur. So ...
946 views

### Clustering time series with wavelets in R

Can discrete wavelet trasform be used for feature extraction from time series in order to cluster them? Any R code how to do this will be appreciated.
325 views

### Identifying fraudulent questionnaires

Questionaires are often used in social sciences. Many people try to complete them very quickly and very often they only "guess" answers. Is there any statistical technique or any research in this ...
876 views

### Can this be considered close to normally distributed?

I have a series of data looking like this, and I wonder if this can be considered to close to normally distributed, even if it has a tail to the right? Can I use t-tests and define "large" being over ...
2k views

### When is quantile regression worse than OLS?

Apart from some unique circumstances where we absolutely must understand the conditional mean relationship, what are the situations where a researcher should pick OLS over Quantile Regression? I ...
1k views

### Assessing scale reliability: how to get the p-value for corrected item-total correlation?

I assessed the internal reliability of a self-created scale with eight items ($N = 150$) by calculating Cronbach’s $\alpha$. It appears that one item correlates low with the overall score of the scale ...
43 views

### Would it be appropriate to calculate the odds ratio while comparing difference in risk factors for a given disease between two genders

I recorded risk factors for a given disease and then compared them between the two genders. I have calculated the p value as well to assess the statistical significance. In the current scenario, would ...
269 views

### Overall type I error with dependent tests

Imagine we test 2 dependent samples: For example, we first test an overall sample (treatment vs. control) and then a subset of this overall sample (treatment sbg vs. control sbg). In this case, we are ...
2k views

### Using lme to analyse a complete randomized block design with repeated measures: Is my model correct?

I've got a completely randomized block design with three treatments and four replications. Biodiversity was measured in four successive years. I figured that a mixed model with repeated measures as ...
142 views

687 views

### Deseasonalizing count data

I used stl() in R to decompose count data into trend, seasonal & irregular components. The resulting trend values are not integers anymore. I have the following questions: Is stl() an ...
4k views

### Choosing complexity parameter in CART

In the rpart() routine to create CART models, you specify the complexity parameter to which you want to prune your tree. I have seen two different recommendations for choosing the complexity ...
53 views

### Factoring risk of ruin into binomal calculation

Say I'm flipping coins and betting £1 on each flip. After 100 flips with infinite money, I have an 18.4% chance of being up by £10 or more (binomial with p = 0.5, n = 100, x = 55). If I start with a ...
74 views

### Balancing servers and users

Looking for some direction here. I have a model for a project where I need to balance a bunch of users amongst different servers based on their usage. For example, the heaviest users get placed on ...
6k views

### How robust is the independent samples t-test when the distributions of the samples are non-normal?

I've read that the t-test is "reasonably robust" when the distributions of the samples depart from normality. Of course, it's the sampling distribution of the differences that are important. I have ...
666 views

### Mean residual life

If X is a nonnegative random variable representing the life of a component having distribution function F,the mean residual life ...
77 views

### How to estimate 5 percent breaking point of a sample of ropes?

The breaking strengths in pounds of five specimens of rope were 660, 460, 540, 580, and 550. How can I estimate the point at which only 5 percent of such specimens would be expected to break?
5k views

### Why is the Jeffreys prior useful?

I understand that the Jeffreys prior is invariant under re-parameterization. However, what I don't understand is why this property is desired. Why wouldn't you want the prior to change under a change ...
86 views

### Intuition behind result for binomial

We are given the following equality: $B(k;n,p)=B(k;n+1,p) + pb(k;n,p)$ where $B$ is the binomial cdf, $b$ is the binomial pdf, $n$ is the number of trials and $p$ is the probability of success. How ...
539 views

### Specifying the Form of Prior, Likelihood and Posterior Distributions for Bayesian Analysis

I have recently begun to look into Bayesian Analysis, and, although I'm beginning to get to grips with the general framework (i.e. $\text{posterior} \propto \text{likelihood} \times \text{prior}$), ...
66 views

### What makes values from two features equal for the purposes of constructing a maximum entropy model?

I'm looking to construct a maximum entropy model using general iterative scaling. In the process, I've come across the SharpEntropy project for .NET and I'm using that as a reference for the ...
249 views

### Inequality for bivariate normal distribution

Let $X_1$ and $X_2$ be bivariate normal with mean $\mu=(0,\mu_2)$, for any $\mu_2$, and correlation $\rho$. Consider the following inequality: \begin{align*} Pr\left\{|X_1| \ge ...
772 views

### Looking for ways to compare between coxph models

I'm running Cox proportional hazards regression in R, and would like to test the option of categorizing one of my continuous variables to factor (I'm aware of the loss of data issue, just checking). ...
454 views

### Unfold degrees of freedom of interaction in factorial design analysis in R

I've been trying to analyse data from a factorial design with missing cells without much success until now. I'm using Anova from car package, that, according with I've read, can handle unbalanced data ...
278 views

### Predicting time interval based on statistics

Let's say, we have some random event. We also have a hist of time intervals between two events, based on statistical data. For example, a frequency distribution: ...
90 views

### How to understand the notation behind the standarded residuals?

I don't understand my lecture notes. It states that standarded residuals is by definition $$R_i=\dfrac{y_i-\hat{y}_i}{\sqrt{\dfrac{1}{n-2}\sum_{i=1}^n (y_i-\hat{y}_i)^2 }}$$ I understand that I can ...
46 views

### If I have good reason to expect a certain value as the sample mean and I obtain something very different, should I obtain another sample?

In my specific case, I am measuring the mean of a sample for different values of a factor (let's say the possibilities are integers from 1 to 100). I have very good reason to expect the mean of each ...
49 views

### Computing and comparing semantic networks generated by grouped individuals

I have 2 groups, each containing 20 individuals. For each individual I have a dissimilarity matrix of a number of judged items. I'd like to evaluate whether there is an overall difference between the ...
804 views

### High-dimensional Regression Datasets [closed]

Am looking for pointers to publicly(online) available high-dimensional regression datasets for evaluating my research work. By high-dimensional, am looking for regression datsets with the number of ...
235 views

### Linear mixed effects vs. Repeated Measures

I have 46 replicate trees I sampled in a 2 year study. My objective is: To estimate the proportion of variation among-trees w/in year, and proportion variation due to among year and tree interaction. ...
60 views

### When should one _avoid_ Bootstrapping? [duplicate]

Possible Duplicate: What are examples where a “naive bootstrap” fails? Perhaps this question will turn out to be a bit soft, but I think it may have a hard answer. Feel free to ...
142 views

### Random forest like techniques (bagging, random feature subset) for SGD methods

Are there any well-known results/tools/literature on using bagging and random feature subset selection for regression or SGD-based methods?
232 views

### What function of distance for the questionnaire data?

I have data from questionnaire from school. First question is study program (only 2 programs) and next 35 questions are various questions (influence of friends etc.) Possible answers for 35 questions ...
304 views

### Can you reproduce this chi-squared test result?

Over at Skeptics.StackExchange, an answer cites a study into electro-magnetic hypersensitivity: McCarty, Carrubba, Chesson, Frilot, Gonzalez-Toledo & Marino, Electromagnetic Hypersensitivity: ...
206 views

### What does “return rate” mean in population ecology models?

What does "return rate" (tasa de retorno in spanish) mean in population ecology models? In context of capture-mark-recapture models. I have found many articles on ...
270 views

### What is the nonparametric variant of multivariate ANOVA with more than one one factor (and with interactions between factors)?

I analyze real data where assuptions of classical multiway (more than one factor assumed) MANOVA (more than one response variable) are not met (normality, equal variances). Is there any nonparametric ...
468 views

### An incremental Gaussian mixture model

Question 1: Suppose that data is modelled by a mixture of K probability distributions which are actually Gaussians. $P(x_i|\theta_j)$ is the probability density of the j'th cluster, for which the ...
Suppose $X_1, X_2, ...,X_n$ are samples from a uniform discrete distribution with probability 1/3 on each of the points $\theta-1, \theta, \theta+1$, where $\theta\in\mathbb{Z}.$ From "Theory of ...