# All Questions

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### Test of single proportion - how do i know population proprotion?

I have a study where I did a sample size calculation using N=2800, CI=95%, margin or error = 3.5% to yield n=613. In the study (auditing of charts), I wanted to look at the error rate in my sample. I ...
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### PCA on vaguely sinusoidal data

I have data that is vaguely sinusoidal/periodic - there is variation in different periods, but in more than amplitude and the length of a period. I've been told to use pca to figure out the primary ...
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### How we can calculate squared factor loadings in Principal Component Analysis (PCA)?

This snapshot is from THIS article: What is Squared factor loadings and how we can calculate it. Is this same as below output of SPSS? there isn't any relationship between two snapshots.
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### Why does the normality of the coefficient's probability distribution follow from the normality of the errors in OLS?

So suppose after an OLS regression we want to know what the chance is that the Beta coefficient is 0. First we assume that many random processes caused the errors ($\epsilon\!_t$), meaning that the ...
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### Matlab's sizing of exogenous inputs to vector time series

Matlabs commands for analyzing vector time series (e.g., vgxvarx, vgxproc) accept exogenous inputs. I understand the explanation that each of p inputs can have q paths with r observations, requiring ...
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### Normalizing criminal activity

I want to compare criminal activity with other factors(education, gdp,...) if and how are they correlated, but before I start drawing graphs I need to first shape my numbers in to useful data. I got ...
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### Frequency stability property

I have seen this short, wonderful video about the frequency stability property (also there is another video from this guy under his kickstarter project ArtOfTheProblem; they are both great, and I ...
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### Performing hyperbolic regression in SPSS [on hold]

I am interested in computing a fitted value $k$, for a given dataset of a dependent variable $V$ and an independent variable $D$. The regression model should be of the form $V = 10/(1+kD)$. Can ...
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### Latent variable values in structural models

I am beginning to go through SEM textbooks and research in order to understand the logic and reasoning for the analysis. I believe that I will be using this type of analysis in the near future for my ...
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### Correlating Percent Change

I have heard in the past that it is 'dangerous' to run a correlation analysis on two percent changes. Such as a situation in which you are trying to make a link to a medication or other treatment and ...
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### Independent variable has a known non-causal relationship with the dependant variable; is it still okay to regress?

To further elaborate on my question, assume that I have a time series dataset of Tax X and Tax Y, where in Tax X is paid by 100% of the sample while Tax Y is paid by 75%. Both taxes differ with ...
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### pvalues of glm coefficients and heavy tailed distributed residuals

I've seen this post but I have still some additional questions. I have a glm model with a continous response and a couple of hunderd predictors (which represents different conditions). I want to know ...
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### R, Pairwise comparison of random variable in mixed model

We measured temperatures of a pond repeatedly every day at each hour for a month at two different depths (i.e., top and bottom). We want to see if the temperatures at the top of the pond are ...
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### How to deal with garbage data with Random Forest?

I'm using scikit-learn's RandomForest to perform a multi-class classification task, with examples from N classes and "garbage" examples not from the N classes. Because the garbage examples might ...
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### Least Squares Regression Step-By-Step Linear Algebra Computation

As a prequel to a question about linear-mixed models in R, and to share as a reference for beginner/intermediate statistics aficionados, I decided to post as an independent "Q&A-style" the steps ...
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### Is the MAP estimate always identical to the ML estimate when a diffuse prior is used?

Let's say I have two normally distributed variables: say height and body mass. I want to estimate the Pearson's correlation coefficient between them. I have a model that estimates the mean and SD of ...
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### Model checking versus posterior predictive checks

I am interested in knowing if there are any difference in modeling checking versus posterior predictive checks in the Bayesian framework. Are posterior predictive checks a type of model checking?
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### Why are server response times distributed lognormally?

I found out that webserver response times are typically modeled as coming from a lognormal distribution here. What I don't quite get is why this is the case! In particular, Wikipedia states that a ...
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### Sample size calculation for correlation study

I am planning a study to assess the correlation of perceived stress in medical students and their academic performance. After a literature review, it appears that one previously done recent study has ...
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### Ordinary and SVM regression fought, who won? [on hold]

Suppose one would like to construct a regression model for solely prediction purposes. Which one is better and when, ordinary or SVM regression?
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### “Overlapping” variables in partial correlation

Here is my problem: imagine I am studying the relationship between the frequency of swearwords in a book (per 1000 words) and the number of chapters in the book (I’m making this up – I’m really ...
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### When to stop an ad campaign?

I have a campaign and I am trying to decide whether to terminate or not, with profit maximization in mind. There is cost associated with every time the ad is shown, and a reward once it converts ...
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### How to check statistical significance

I am not at all good in statistics and totally new here. My doubt may be very simple or foolish, please don't mind. I am from Civil Engineering background. In an experimental work, I am comparing ...
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### How do you distinguish between these two types of data?

The two types of data differ in that if you decide to decrease the temporal resolution of the first type of data you take the mean of lower resolutions. With the second you take the sum over the lower ...
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### What is the difference between predict() with and without offset-term when using vglm() of the VGAM package in R?

I am fitting a regression model based on the generalized poisson distribution. Here is an example ...
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### Interpretation of the magnitude of the effect of interaction terms

I have a model with interaction terms: $Y = a + b X_1 + c X_2 + d Z + f X_1 Z + g X_2 Z + error$, where $X_1$ and $X_2$ are (0,1) indicator variables and $Z$ is a continuous variable (with a ...
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### Deriving mean of percentages from clustered data

I am getting into a roadblock about how to analyse this data set. I hope folks here will be able to give me some hints and suggestions. Here is an example of the data: I'm using sugar as the ...
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### How many experiments for measuring of standard deviation

I want to get standard deviation of variable. How many data I need to to obtain correct value? What is correct approach to estimate amount of data I need? What precision I need to say it is precise ...
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### watershedding vs mean shift clustering

I'm working on a clustering problem, and I was trying to understand the difference between the watershed algorithm and mean shift clustering. It seems that these algorithms are popular for image ...
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### Correlated slopes and intercepts in lme4

I have what I think is a simple question. I have run a simple linear mixed model using lme4. It is a random slopes and intercepts model and I am looking at how these intercepts (B0) and slopes (B1) ...
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### Number of combinations with elements from different sets

Unfortunately I could neither find nor develop a closed formula, but I believe there is a simple solution for this problem. Could you please help me? Suppose that there are 4 different sets: Set A, ...
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### How to deal with the “sure probabilty” (p=1) in logistic regression

The model of logistic regression is that: log(p/(1-p) = ...... The most interesting case (for me) is the case that we have p=1 and p=0. But in this case, the ...
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### Reference help MCMC

I am studying on Markov chains, random walks, gibs chains and optimizations using methods such as bisection and Newton Raphson, but am finding that the references that I have a little complex, like to ...
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### Gap test for random number generators

Gap test is discussed here http://math.stackexchange.com/questions/270377/gap-test-for-random-numbers/1301443?noredirect=1#comment2643072_1301443 , if we have probabilities how we can find the ...
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### Clustering stream of new customers based on future potential

I need to cluster new customer according to their future potential, but I have only information about their first transaction. I have access to all transactions for the other customers. So I can do ...
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### LASSO with two predictors

I have a question regarding LASSO with two predictors, somewhat related to another one of mine posted here. I am trying to illustrate equation (6) of the original paper by Tibshirani, JRSSB 1996, ...
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### Help in identifying this nonlinear system

In the paper: http://inds08.uni-klu.ac.at/INDS2008/INDS08_System_Identification_using_Symbolic_Chaotic_Sequence.pdf there is a chaotic map in Eq(11) c_{n+1} = \frac{\gamma c_n(1-c_n^2)}{1+\rho ...
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### General assumptions about functions in machine learning

In the article "A few useful things to know about machine learning" (ungated pdf), I found the following quote: In fact, the general assumptions, like smoothness, similar examples have similar ...
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### Impulse Response Analysis for Markov-Switching Models

I've estimated a bivariate Markov-Switching VAR(1). I am interesting in understanding how an error/ 'shock' would propagate through the system. I've been stuck on how this could be done? Thank you!
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### For a longitudinal observational study, what is the best method of comparing cost before and after intervention?

I have a sample of 200 patients, with data for 2 years. During year 1 they are on treatment A and accumulate overall healthcare costs of X. During year 2 they are on treatment B and accumulate ...
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### Use of MICE to derive imputed values [on hold]

Anyone have a moment to assist with determining why I have an error with my sample data set up to run MICE? I keep getting an error in D.F. when I run this command line with my data. I am using this ...
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### Generation of data from a bivariate distribution

Let $X$ and $Y$ be non negative random variables with joint distribution $$F(x,y)=1-e^{-x}-e^{-y}+e^{-x-y-\delta xy}; ~~~x\geq 0,~~y\geq 0.$$ How to generate a bivariate ...
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### Definition of p-value in carets confusion matrix method

In the documentation for the confusion matrix method in the caret package, the p-value is described as: a one-sided test to see if the accuracy is better than the "no information rate," which is ...
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### Binning by standard deviations

Quick question: I came across a fairly respected source on running Markov Chain Monte Carlo for bayesian statistics in ...
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### Compare distributions (with replicates) and visualization

The experimental set-up is an almost typical control vs treatment, in which we are counting how many reads map to a particular class of genes in each condition (RNA-seq), done in triplicate. An ...
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### Repeated measures: Relation between baseline adjusted ordinary regression and random intercept model

I'm currently trying to familiarize myself with linear mixed models (with normally distributed continuous outcome, no generalized versions for the time being). One particular question I'm currently ...
36 views

### Time series Analysis using LS

I know this is a bit of a broad question but generally if I have a time series and I want to measure whether it has trend according to time I do the following: I regress the series against time, ...
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### Non significant Tukey's pairwise tests for glm with significant anova

I have run a glm poisson log model for counts in R and obtained a significant p value for the anova. However, my Tukey's pairwise comparisons are all not significant. What should I do to identify ...