# All Questions

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322 views

### Temporal trend visualizations for regions

I try to reproduce a plot which I found in a publication (Mayor-Fernández et al 2012) showing unemployment rates across time for several regions. It combines a heatmap (?), a time series plot (lower ...
536 views

### Sample size for multiple regression: How much more data do I need?

I'm trying to test a prediction from a computational model with a biological experiment. The model predicts a linear dependence between cell size and asymmetry. I performed an experiment that is ...
6k views

### Confusion regarding correlation and mse

I have a dataset containing three variables. I have this confusion, low mse means higher correlation isn't it? Now when I calculate the mse for variable two and three where the third variable is my ...
135 views

### Convergence of MCMC for ill-behaved functions

We are doing MCMC sampling over an n-dimensional space with a population of MCMCs. The goal is to have them stop when they approximately converge. The problem is that the convergence, which is so ...
15k views

### Whether to use original or reverse coded items in factor analysis?

I am currently analyzing data from a 34-item Likert scale. I already recoded the negatively stated variables in SPSS as different variables. I'm about to do a factor analysis. Should I use the ...
257 views

### To aggregate and lose resolution OR not to aggregate and suffer with correlated binary data?

I have data from an experiment in which each participant provides a binary response to each presented stimulus, which is either correct (1) or incorrect (0). There are 4 different stimulus types, ...
204 views

### Testing whether there is a difference between two groups who were asked the same set of questions

I asked two groups of individuals (80 males and 10 females) fill out a questionnaire asking them their attitude towards a series of political variables. Every individual had to answered a set of 16 ...
37k views

### Which result to choose when Kruskal-Wallis and Mann-Whitney seem to return contradicting results?

I have these groups where the values are responses to a 10-point Likert item: g1 <- c(10,9,10,9,10,8,9) g2 <- c(4,9,4,9,8,8,8) g3 <- c(9,7,9,4,8,9,10) ...
4k views

### Confidence intervals around a centroid with modified Gower similarity

I would like to obtain 95% confidence intervals for centroids based on Gower similarity between some mulivariate samples (community data from sediment cores). I have so far used the ...
2k views

### What level of measurement is a factor score?

After doing a factor analysis, I decide to use that factor to test a hypothesis. However, I am not sure what data type of the Factor score the is (i.e., nominal , scale, etc.). Can I do a t-test or ...
24k views

### How does ties.method argument of R's rank function work?

I am using rank(a, ties.method="max") to rank a. But I am not quite sure what does ties.method="max" do. Can you please help?
148 views

### Does anyone know how this visualization was made? [closed]

I've been tasked with implementing a visualization something like this one from the New York Times: http://www.nytimes.com/interactive/2012/08/05/sports/olympics/the-100-meter-dash-one-race-every-...
278 views

### What test should I choose if I want to see if two groups are different from each other in many categories?

I am currently analysing data of a big webshop with over 31,000 vendors selling goods, i.e. each vendor is selling items over the webshop. The cool thing is that we know the gender of these vendors (=...
2k views

### Differences between Stata & SPSS in multiple regression outcomes

I'm a graduate student working on a thesis whose aim is to test complementarity between 2 practices (CI and INNO, according to theory of supermodularity). To do so, I calculated two new variables (...
2k views

### How to know the stochastic gradient descent is converging when the objective function is expensive to compute

How can I know if the stochastic gradient descent algorithm is converging. I cannot plot my objective function and take its average for lets say every 1000 iterations to see the trend. My objective ...
762 views

### Shouldn't the beta estimates always be the same using lm and lmer?

Can anyone tell me under what conditions the beta estimates differ between lm and lmer with a random intercept? I came across a situation where the fixed effect differed considerably. I thought the ...
51 views

### Can a different indexing approach improve the relevance and efficiency of search engine results?

I am creating a search engine, with the corpus consisting of websites crawled through a webcrawler (Apache Nutch). I need the query searches to be both fast and relevant. So far, I have been trying to ...
155 views

### What are possible reasons for differences in numerical output from the same procedures performed in different statistical packages?

My colleague and I do the exactly same thing with the exactly same data and get different results. He uses Stata, I use R. We both use 32-bit Windows machines. Are there any possible explanations ...
106 views

### How to build a predictive model using sound (frequency and amplitude) as the input

I'm working on a medical research project where we're looking at the changing resonances in femur bones during hip replacement operations. Some surgeons use the increasing pitch of the bone resonance ...
5k views

### Concepts behind fixed/random effects models

Can someone help me to understand fixed/random effect models? You may either explain in your own way if you have digested these concepts or direct me to the resource (book, notes, website) with ...
96 views

### Resources for developing prognostic index-scores

I am looking for online resources or books explaining how to develop prognostic indexes-scores step by step. I am mainly wondering about model validation and transformation of regression coefficients ...
992 views

### Double exponential smoothing in multivariate multilevel panel regression

I would like to use double exponential smoothing to predict prevalence rates of care dependency in Austrian federal states. My data is very detailed, thus I would like to make use of that in order ...
683 views

### At what VIF level should you switch from OLS to ridge-regression?

Regarding multicollinearity, is it recommended to use ridge-regression if you have some covariates with VIF values around 10 in the OLS model? What would be the best VIF level to use to decide ...
78 views

### Dirichlet density with just one x value and one alpha parameter

Does it make any sense to apply the Dirichlet density function to only one x value and therefore one alpha parameter? (this would be the result of some bin merging) I'm asking because it appears ...
191 views

### Find the mean and variance of $U_1 + U_2$

Let $Y_1, Y_2, Y_3$ be i.i.d continuous random variables. For $i = 1, 2$ define $U_i$ as $U_i=1$ if $Y_{i+1} > Y_i,$ $=0$ ,otherwise Find the mean and variance of $U_1 + U_2$ I can't find the ...
3k views

### Model selection and model performance in logistic regression

I have a question about model selection and model performance in logistic regression. I have three models that are based on three different hypotheses. The first two models (lets name them z and x) ...
157 views

### Can I compare correlations even though one is NOT significant?

I have 2 groups and 2 correlation coefficients that I would like to compare using Fisher's transformation. Unfortunately, one of these coefficents is not significant, so not different from zero. Can ...
2k views

### Analyzing repeated measures ANOVA with two groups

I have a data set that looks like this: ...
369 views

### Dynamically adjusting NN architecture: inventing the unnecessary?

I am starting out on my PhD journey, and the ultimate goal that I set before myself is developing ANNs that would monitor the environment they work in and dynamically adjust their architecture to the ...
643 views

### How to find a breakpoint for each ID in a linear regression model with R?

I have some repeated measures with 196 individuals and some of my regressions have a plateau. So I want to characterize this with an eventual breakpoint for each ID. Example: subset of my personal ...
225 views

### Evaluating model performance without validation data

I've found myself in a situation where I have been given a model that has been developed from what I believe to be the "this seems right" approach. The model in question is very complex but it has no ...
26 views

### dirichlet density function returning values > 1.0 [duplicate]

Possible Duplicate: Probability distribution value exceeding 1 is OK? I'm comparing results given by this implementation and that from the gtool library in R, of the Dirichlet density function. ...
4k views

### Subsample bootstrapping

I have been working on the uncertainty associated with a quantity calculated from a Monte Carlo project. Normally I would use the bootstrap method by resampling with replacement, for a couple of ...
508 views

### Dense Data Compression (Delta Encoding?)

Let $X$ be a dense integer set such that its elements are closely knit in value. For instance: 1 1 1 1 2 2 2 2 2 3 3 5 5 6 6 6 6 6 7 7 7 7 8 8 8 8 8 8 ... I am ...
59 views

### Estimating a time frame for interventions or judging the extent to which events become “determined” as time goes on

In certain arenas, it's valuable to be able to intervene early on to prevent problems from getting worse, because after a certain point there's not much you can do. Two examples might be public health ...
282 views

### Compute $\mathrm{Cov}(\sum_{i=1}^NX_i,\sum_{i=1}^NY_i)$

Let $X_1,X_2,\dots$ be i.i.d. Bernoulli random variables with parameter $\frac{1}{4}$. Let $Y_1,Y_2, \dots$ be another sequence of i.i.d. Bernoulli random variables with parameter $\frac{3}{4}$. And ...
245 views

### Is Ye Shiwen's 400m IM performance in Olympics “anomalous” statistically?

The 16-year-old Chinese swimmer Ye Shiwen swam more than 5 seconds faster than her personal best in women's 400m individual medley in London 2012 Olympics, winning her a gold. Her performance received ...
669 views

### Group-level correlation effect

I am measuring two continuous variables ($X,Y$) for 21 subjects. $X$ and $Y$ have 216 data points each (per subject). I would like to see if $X$ and $Y$ are correlated at the group level. I can think ...
3k views

### How to build a regression model with just 5 datapoints with 5 or more variables?

I am attempting to build a simple multiple regression in order to estimate the value of a home. The 5 datapoints are 5 comparable home sales (similar in size, lot, location, # of bedrooms, etc...). ...
66 views

### How to define and model consumption bundles?

Imagine an a la carte buffet with n different rooms. On entering the buffet you pick a room (let's say American, Mexican or Italian food) where you stay for the duration of your visit. Once in a room,...
2k views

### Modelling a binary response variable with a binary explanatory variable

I'm modeling (using GLM) one binary explanatory variable against a binary response variable. The output looks ok to me, but I'm a biologist with a basic knowledge of stats, I just wanted to ask if ...
14k views

### How to perform pooled cross-sectional time series analysis?

For 86 companies and for 103 days, I have collected (i) tweets (variable hbVol) about each company and (ii) pageviews for the corporate wikipedia page (...
131 views

### Inferring multiple ratios and binomial proportions with missing data

I have a number of studies describing families tested for a genetic condition. For each study the following data are described: $n_p$, number of probands (the proband is the first person in a family ...
9k views

### Is there an optimal bandwidth for a kernel density estimator of derivatives?

I need to estimate the density function based on a set of observations using the kernel density estimator. Based on the same set of observations, I also need to estimate the first and second ...
7k views

### How to determine significant principal components using bootstrapping or Monte Carlo approach?

I am interested in determining the number of significant patterns coming out of a Principal Component Analysis (PCA) or Empirical Orthogonal Function (EOF) Analysis. I am particularly interested in ...
143 views

### Statistical test for a gradually self-improving suggestion system

I built a suggestion system, which provides a list of candidate items to users. As users choose some items from the suggested list, the system remembers those choices, and the next time the system ...
587 views

### How do you identify the variables that separate several groups?

I don't have much background on statistics. I am working on multivariate morphometrics of a sample of frogs. I have a data matrix of 19 variables (continuous characteristics) for around 250 samples. ...
814 views

### Sample session for analysis of conjoint data in R

While I have successfully used R for Cluster Analysis and Correspondence Analysis, I'm new to the use of R-project for Choice-Based Conjoint. Per recommendations in this post, I'm looking at the ...