# All Questions

21 views

### Help with dummy variables

Can you please help me with 2 questions (both to do with dummy variables) - 1) If I have 2 sets of nominal variables (eg ethnicity [white, Indian, African] and smoking status [current smoker, ...
21 views

### LDA with three variabilities

In a classical linear discriminant analysis (LDA), we usually have only two variabilities to handle (the between classes and the between individual variability). Usually LDA is used to maxmize the ...
47 views

### $H_0=250g$ and $H_1\neq 250g$" [on hold]

We have a sample of size $100$ with a standard deviation of $5g$ It was decided that if the sample mean is between $245g$ and $255g$ while the sample average is $250g$ if $\mu=250g$ or $\mu\neq250g$ ...
32 views

### Bartlett's test vs Levene's test

I am currently trying to address violations to ANOVA assumptions. I have used Shapiro-Wilk to test normality, and have dabbled with both Levene's test and Bartlett's test of variance equality. I have ...
48 views

### Testing correlation and the t-statistic used in Simple Linear Regression

Given $H_0$ : $\rho=0$ and $H_A$ : $\rho\neq0$, we use the test statistic $t_{n-2}$ , which is $\frac{r\sqrt{n-2}}{\sqrt{1-r^2}}$. I have to show that $\frac{r\sqrt{n-2}}{\sqrt{1-r^2}}$ equals ...
30 views

### Meta-analysis: Difference between direct and indirect restriction of range

Looking at meta-analysis for personal selection procedures, I am having really big troubles to figure out the difference between concepts of direct restriction of range (DRR) and indirect restriction ...
28 views

### Forecasting in Stata

I am working with time series data and fitting an autoregressive model using OLS. For reference, here is my price data for the commodity (I am not sure how to better format data for this site): ...
46 views

### Coupon collecting problem

Suppose there are 8 different types of coupons, each coupon has probability 1/8 of being selected. Suppose a total of 6 coupons are collected. Let:  X_i=\begin{cases} 1, \textrm{if a type-i coupon ...
16 views

### Dependent variable is non-stationary and independent variable is stationary - residual series?

I ran a regression model where dependent variable is non-stationary (I know this is wrong) and my independent variable is stationary...I find that the residual series are stationary... how is it ...
14 views

### How to make series stationary when dependent variable is log(y)

I need some help in understanding the following: I have a time series data (y) that I am using to run regression models. However, my dependent variable is log(y). Should I test for stationarity of ...
689 views

### Should the fumble rate of NFL teams be a normal distribution?

There's a lot of garbage statistics going around the internet regarding the Patriots, but I was just curious what the well-versed in statistics have to say about this. The main question is - in what ...
21 views

### Is this a job for mixture of experts regression or semi-hidden markov models or something else?

Data I have several thousand timeseries each comprising around 365 data points. Browsing through a few of them, it looks like each timeseries consists of several regimes (different number f regimes ...
26 views

### A popular name for a parameter vector? [on hold]

I have implemented a simple model fitting algorithm based on linear regression. And because I learned it that way, I have called the parameter vector theta. But as this is relatively big project, ...
13 views

### A Hypothesis Testing Question and Verification

Suppose we have two p.d.f.'s: $f_0(x)=1,$ if $0\leq x\leq1$, and $f_0(x)=0$ otherwise $f_1 (x)=2x$ if $0\leq x\leq1$, and $f_1(x)=0$ otherwise We want to test the hypotheses ...
66 views

### Explained variation ($R^2$) from MCMC glmm - Nakagawa & Schielzeth 2013

This is a follow up to a question I asked previously, where I suggested that variance-covariance matrices could be used to derive correlations, which are then usable as estimates of how much each ...
24 views

### Log posterior function in PYMC

my question concerns the logp function in the PYMC package in Python. Ultimately I want to calculate a quantity that goes by many names, namely the Bayes-factor/ evidence/ marginal-likelihood of the ...
18 views

### Base sales in multivariate time series | MCMC model

I have been looking around online for good resources that explain how one would go about calculating base sales when preforming marketing mix modeling. I was told by a colleague that essentially they ...
23 views

### Which significance test can be used in this instance? - paired, non-normal means

I have a data set of behaviours for a herd of captive elephants which I have attempted to quantify to compare for statistical significance, i.e., if a behaviour is performed once during an observation ...
48 views

### How to use LASSO to select glm model gaussian

I have a small sample size n<20. I want to find which combination of 8 variables better predict y. I was using a stepAICc but it is suggested to away stepwise model selection. I have tried lars ...
20 views

### Effect of Lag time between explanatory variables and response on linear regression

I am curious as to how lag time between explanatory variables and response variables affect linear regression models. I am looking at some environmental data, mainly precipitation, temperatures, and ...
9 views

### Analysis of clustered data

I have records of $multiple$ visits from many different patients in several different clinics (i.e. visits nested within patients nested within clinic) and plan to perform an analysis that takes into ...
13 views

### Predictions using time dependent covariates in survival model [migrated]

Simple question, how do you specify time dependent covariates in the data.frame supplied to newdata when looking to make predictions? In other words, I fit a model ...
75 views

### Standard error of regression coefficient without raw data

After searching here: Perform simple regression without raw data I am still curious about this. Is it possible to derive the standard error of a regression coefficient from summary data alone? ...
25 views

### Dirichlet Processes for clustering: how to deal with labels?

SHORT VERSION Can we cluster data based on a Dirichlet Process? When using Gibbs sampling clusters appear and dissapear. Can we summarize the class assignments with this or some other scheme or ...
9 views

### compare magnitude of association between pairs of discrete variables?

say I have discrete(nominal) variables Y, X1 and X2. X1 and X2 have different number of levels. I want to assess whether Y is associated more with X1 or X2. I understand that I could use chi-square ...
24 views

### How to apply an R prediction model to very big data from SQL database in parallel.

I dont need to load the entire dataset into memory. In fact I only need 1 row at a time to apply a trained model, get the predicted response and put that response somewhere, possibly back into another ...
79 views

### Variance estimation in a one-factor linear model

I was given a dataset (a mat file) of $100\: 000$ observations, each with $50$ dimensions (coordinates). Denote matrix $X$ a $50\times 100\:000$ matrix in which each column was generated according to: ...
18 views

### Model selection and performance evaluation using cross-validation for time series with missing values

So my task is to select and evaluate a statistical model (random forest, boosted trees, neural networks etc.) for a time series with missing values around 10 years long. One of the goals of that is to ...
17 views

### Developing a heuristic for maximizing the “covering” of a distribution

Context There's a board-game called Settlers of Catan in which players compete to be the first to gain 10 victory points by trading various resources in exchange for pieces (or cards) worth victory ...
29 views

### why the non-seasonal and seasonal parts are multiplied in ARIMA models?

I would like to understand why the non-seasonal and seasonal parts are multiplied in Seasonal ARIMA models. To be more specific: when we use the Seasonal ARIMA model we assume a multiplicative ...
15 views

### How do I report the weights of the most influential features for logistic regression?

I am currently using logistic regression to compute the probability of some event. I randomly split my training/test data and perform cross-validation on the training data, getting a "best model" for ...
21 views

### Significance codes in linear model with factors

I am setting up a linear model in R and need help understanding the significance codes when one of my independent variables is a factor - i.e., dummy variable for each possible value For a scalar ...
23 views

### Gaussian or Dirichlet Process from aggregated samples

For N individuals, I have the number of measurements taken per individual, the individual's mean measurement value, and the standard deviation of the individual's measurements, but I do not have ...
9 views

### Breusch-Pagan Test in Weighted Least Squares

When fitting an ordinary linear regression model, we can conduct a test for heteroscedasticity by applying the Breusch-Pagan Test. We fit the linear model, calculate the residuals, and then regress ...
42 views

### confidence intervall for the product of random variables

Suppose $X_i\sim N(\mu,\sigma^2)$ and $W_i\sim \text{Uniform}(0,d)$ are independent random variables for $1 \le i \le p$ and $p$ is large. Given $0\lt\alpha\lt 1$ and a number $c \gt 0$, I need to ...
8 views

### Obtain Precision and Recall from Click through data

I am trying to build a graph of precision and recall using click data. I have two data sources. First data source has all the user clicked item_ids based on a given query_id. Second data source has ...
19 views

### Intrinsic dimensionality estimation using Laplacian Eigenmaps

I learnt that I can look at the eigenspectrum of the kernel matrices computed by nonlinear spectral techniques in order to estimate the intrinsic dimensionality of a data-set. I use drtoolbox (The ...
92 views

### Is the triangle inequality fulfilled for standard hierarchical clustering distances?

For hierarchial clustering I often see the following two "metrics" (they aren't exactly speaking) for measuring the distance between two random variables $X$ and $Y$: $d_1(X,Y)=1-|Cor(X,Y)|$, ...
6 views

### FE Model: independence of residual and firm specific component

I'm estimating a fixed effects model and want to consider Petersen's (2009) suggestion: "The components of X (μ and ν) and ε (γ and η) have zero mean, finite variance, and are independent of each ...
13 views

### Warning in SPSS when I run a multilevel model [migrated]

I ran the following syntax and each time I get a warning message from SPSS which says: "Mixed Iteration was terminated but convergence has not been achieved. The MIXED procedure continues despite this ...
40 views

### Why is it the case that when we try to fit an OLS model to a system with more variables than observations, that the residuals are zero?

I am trying to fit an OLS model to some data, where the number of variables $k$ is greater than the number of observations, $N$. In this case, it is obvious that we will have a infinite amount of ...
44 views

### Comparing data that has been recorded on two devices

I have two data loggers which are recording a physiological signal. Device A is a system that has been in place for many years, and records data ~once/minute. Device B is a prototype device which ...
8 views

### Creating a model for a webshop

I'm going to create a Multi-armed bandit algorithm to handle recommendations for a large scale webshop. I'm going to use Thompson sampling (http://en.wikipedia.org/wiki/Thompson_sampling) and would ...
5 views

### least squares with seasonal component in matlab [migrated]

I was reading a paper which looked at investigating trends in monthly wind speed data for the past 20 years or so. The paper uses a number of different statistical approaches, which I am trying to ...
24 views

### Likelihood maximization: MCEM algorithm versus MCMC algorithm

Hello Everyone this is my first question. I am a particle physicist and I am doing some empirical studiues on parameters estimation using different methods (this might give me some handle to study on ...
8 views

### Proper use of varFunc in gls

I'm trying to find the proper weight structure to "fix" a heteroscedasticity issue. I think I know the issue, the error variance is low when the dependent variable is low and grows as the dependent ...
25 views

### Mclust function of mclust package overfitting gaussians

I'm using the Mclust function of the mclust package in R to fit a mixture of gaussians model. My simulated data obviously has 3 ...
7 views

### Latency distribution analysis

I'm trying to analyze latency distribution in the system. Latencies collected in the following way: maximal observed latency per minute is measured then, if this latency is largest latency seen this ...