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I am attempting to do a icc using the quickicc command following the use of xtmixed. I'm attempting to check repeatability in a sample of 24 individuals with QT measures (a measure of ventricular depolarization). Each individual has various readings of QT; some have 31 whilst others have 5 measured at various times by... |
As an example, consider the ChickWeight data set in R. The variance obviously grows over time, so if I use a simple linear regression like:
m <- lm(weight ~ Time*Diet, data=ChickWeight)
My questions:
Which aspects of the model will be questionable?
Are the problems limited to extrapolating outside the Time range? ... |
I'm thinking of this from a very basic, minimal requirements perspective. What are the key theories an industry (not academic) statistician should know, understand and utilize on a regular basis?
A big one that comes to mind is Law of large numbers. What are the most essential for applying statistical theory to data a... |
How do I add a neat polygon around a group of points on a scatterplot? I am using ggplot2 but am disappointed with the results of geom_polygon.
The dataset is over there, as a tab-delimited text file. The graph below shows two measures of attitudes towards health and unemployment in a bunch of countries:
I would like ... |
I'm trying to find more information on how to measure and detect increases in activity in twitter list activity. I have access to all the tweets produced by a list of users. The idea is to try to predict or detect when there is some breaking news that everyone is talking about.
A sensible thing is to plot number of twe... |
I'm trying to utilize economic and industry data to forecast sales of industrial companies. I have numerous economic and industry indices and as a first step I would like to indentify those indices that are good leading indicator for sales. I have already utilized graphing, but I was hoping there was a statistic that w... |
I have problems interpreting the direction of the effects in my model. Can you help me with this?
I conducted an experiment which includes
between subject factor:
group=2 (coded as 0-1)
within subject factor:
stimulus type=3 (coded as -1 0-1)
empathy questionnaire which I centred (subtracted the mean). Participants c... |
The Wikipedia article Spearman's rank correlation coefficient contains an example for calculating ρ. At the end of the sections is the statement "...with a P-value = 0.6864058 (using the t distribution)." The author does not describe how the P-value was calculated from the data in the example.
How was the P-value deriv... |
Suppose you have a sample of $n$ outcomes and for subject $i$ you observe $Y_{i1}$ and $Y_{i2}$, which are 'before' and 'after' measurements on subject $i$. You have a single continuous independent variable, $X_i$, observed for subject $i$ and would like to explain the before/after difference $D_{i} = Y_{i2}-Y_{i1}$ in... |
Consider the following R code:
example <- function(n) {
X <- 1:n
Y <- rep(1,n)
return(lm(Y~X))
}
#(2.13.0, i386-pc-mingw32)
summary(example(7)) #R^2 = .1963
summary(example(62)) #R^2 = .4529
summary(example(4540)) #R^2 = .7832
summary(example(104))) #R^2 = 0
#I did a search for n 6:10000, the result fo... |
So my data consists of a distance matrix for some points, and a table classifying the points as either red or green. I want to know if there is any difference between the red and green points. I did UPGMA clustering and they don't look different (doesn't seem to be any tendency for red or green to cluster together) but... |
Possible Duplicate:
Calculating percentile of normal distribution
Edit: I think the hint is Box-Muller transformation. Any ideas?
I am trying to find the inverse of normal CDF.
This is normal CDF I got exactly from Wiki,
$\Phi (x)=\frac{1}{\sqrt{2\pi}}\int\limits_{-\infty }^{x}{{{e}^{-{{t}^{2}}/2}}}dt=\frac{1}{2}\l... |
I have a huge multilevel longitudinal observational data of the concentration of certain chemical collected at various sites over 10 years (1990-2010). Sites are classified into different type of sites as A, B, and C. In the dataset year variable is coded as 1990,1991, 1993 etc. At one year, there can be many sample... |
Let $X_1, X_2, ..., X_n$ be an iid random sample from a Poisson$(\lambda)$ distribution:
a) find the UMVUE of $\theta$ = $\lambda^k$ for $k > 0$ a known integer
b) find the UMVUE of $\tau = e^{-\lambda} = \mathbb{P}(X = 0)$.
Edit: I have found that $T = \sum X_i$ is a complete sufficient statistic. It has a Poisson$... |
I wanted to compare how two different (independent) models perform under winbugs, So I created code like:
# likelihood
for (i in 1:sites) {
M[i] ~ dpois(lambda) # model 1
M2[i] ~ dpois(lambda2) # model 2
for (j in 1:sample) {
obs[i, j] <- sum(y[i, j,])
# model 1
y[i, j, 1] ~ dbin(p... |
Let´s say that my PCA analysis extracted 2 components, which explain 80% of the variance before rotation. The components were then rotated using oblique (Direct Oblimin) rotation, so SPSS cannot compute how much percentage of variance each component explain. When I plot the graph, usually editors require these percenta... |
One objective of a survey can be to understand the proportion male vs. female users. To the extent a specific gender correlates to particular use cases of a technology, product design, product/feature prioritization and marketing can be differently managed.
A survey of existing users will inherently have error bars bas... |
I'm trying to compare gaze durations measured using an eye tracker for each word. Since longer words will naturally lead to longer gaze durations, simply comparing the values is inaccurate.
gaze duration word length
100ms 6
250ms 8
150ms 7
A simple way to normalize the values is b... |
It seems that WinBUGS has problems if it has only zero draws from one binomial distribution:
1. case - simple model
for (i in 1:sites) {
N[i] ~ dpois(lambda)
for (j in 1:sample) {
y[i, j] ~ dbin(p, N[i])
}
}
If all values y[i,] are zero, then the following error message appears:
value of order of ... |
I am very new to Bayesian inference and can't figure out what may be an elementary problem. Also, please forgive me if I am screwing up the notation -- this is my first foray into Bayesian statistics.
Set-up: At time $i=0$ I start with a random variable $X_0\sim \mathcal{N}(\mu_0,\sigma^2_0)$. Over time I observe the ... |
I'm looking to generate a set of 5 random variables and enforce a dependence structure between them and onto a dependent variable $Y$. I understand how to generate correlated random variables for multivariate normal, but not when mixing different types. Below is a little more than I need, but I'm hoping someone can g... |
Let's say I have a sample of "events" done by a certain number of subjects, and some (although not most) of these subjects have underwent more than one event. I'd like to fit a logit model to these data to find out which characteristics contribute to a subject, over the course of an arbitrary period of time, undergoing... |
Suppose we are using logistic regression on a binary outcome variable $Y$ with two continuous predictors $X_1$ and $X_2$. Suppose the observation $Y = 1, X_1 = 10, X_2 = 15$ occurs 1000 times. In SAS, how would you account for this frequency in the regression without having to manually type the observation 1000 times?
... |
On the Probability chapter of a 1995 mathematical statistical book I am reviewing I have found the following exercise:
Let A and B be arbitrary events. Let C be the event that either A occurs or B occurs, but not both. Express C in terms of A and B using any of the basic operations of union, intersection and compleme... |
This is for Project Euler problem #371:
http://projecteuler.net/problem=371
My solution was to generate a huge random pool of numbers between 0 and 999 inclusive, repeatedly ask the question 'How many numbers do I need to pull into a holding area before I get a pair that adds to 1000?', and then average the resulting l... |
Suppose we have two vectors of random variables, both are normal, i.e., $X \sim N(\mu_X, \Sigma_X)$ and $Y \sim N(\mu_Y, \Sigma_Y)$. We are interested in the distribution of their linear combination $Z = A X + B Y + C$, where $A$ and $B$ are matrices, $C$ is a vector. If $X$ and $Y$ are independent, $Z \sim N(A \mu_X +... |
I am very interested in learning how to create reoccurring reports from my R code and ggplot2 visualization.
I understand that LaTeX seems to be a possible answer, and to use it with R most use Sweave. And for presentations from R to LaTeX people use Beamer.
My question is, what I should learn first, or what should I l... |
There are words from "The Elements of Statistical Learning" on page 91:
The K centroids in p-dimensional input space span at most K-1 dimensional subspace, and if p
is much larger than K, this will be a considerable drop in dimension.
I have two questions:
Why the K centroids in p-dimensional input space span at ... |
I want to do a CART analysis with multiple dependent variables. Which program is able to do that?
|
A correlation coefficient is lower if there's a low variance in the characteristic of the sample.
For example, the correlation between IQ and school achievement follows this pattern. The correlation is lower if you only include students with similar school achievement. It gets higher if you include students from very ... |
Consider an experiment where a square and diamond appear on a screen, one before the other, and participants are required to judge which came first. Manipulating the time interval between the two shapes and averaging responses to obtain the probability that participants respond "Square came first" typically yields s-sh... |
How can I put in a heading in the tree output when using mvpart()? I am using xv="1se".
e.g. using the spider data in mvpart
fit<-mvpart(zora.spin~water+sand+moss+reft+twigs+herbs,data=spider)
from this I get a tree in R. And I am wondering how to "put in" a heading in this figure.
|
I have a gridded Digital Elevation Model (DEM) which provides terrain elevation ($z$) at cartesian coordinates $(x,y)$. Together with the DEM I know the RMS of the elevations. As far as I understand the RMS can be applied to any point in the DEM and the standard deviation of the elevations is stationary.
Now, if I take... |
When comparing results obtained with different models in R, what should I look for to select the best one?
If I use for example the following 4 models applied to the same presence/absence sample taken from a species dataset, with the same variables:
Generalized linear model
Generalized additive models Classification
R... |
I have a time series of measurements (heights-one dimensional series). In the observation period, the measurement process went down for some time points. So the resulting data is a vector with NaNs where there were gaps in the data. Using MATLAB, this is causing me a problem when computing the autocorrelation (autocorr... |
I want to know if there is any literature about the following regression problem:
$$ Y=X\beta +\epsilon$$
where $Y$ is unknown. But, i know $X$ and the OLS estimator of $\beta$
$$ \hat{\beta}=(X^\top X)^{-1}X^\top Y$$
because i know the value of $X^\top Y$
In fact i have an inverse problem of quadratic programming wher... |
I have this density, I want to find a density "larger" than this
$f(x)=\frac{1}{c}g(x)(1-\sin (20x)/4))$
, where $g(x)$ is N(0,1).
I am looking for a proposal distribution for f(x), basically find a density that is "larger" everywhere than the one above?
I was told to use g(x), but g(x) is not always "larger" becaus... |
I'm confused about how interactions are treated in multiple regressions. When doing a factorial ANOVA, I'd just look at the graphs, say they're not parallel so there's an interaction, run my ANOVA with the interaction term, and determine if it's significant.
However, in multiple regression, I add in my interaction ter... |
Is it possible to define any useful entropy or conditional entropy which is based on the distance between datapoint(s) and cluster center(s), instead of basing on the number of points assigned to cluster like it is defined in for example to compute the v-measure ? I am not implying that I want an equivalent to v-measur... |
I am a beginner in statistics, and am self-studying from "Information Theory, Inference, and Learning Algorithms" by David MacKay. I've hit a wall with one of the questions, and was wondering if any of you could be so kind as to point me in the right direction. Admittedly, my title may be wrong or totally misleading as... |
I have a dataframe with a group variable GRP (ranging from 1-100) and an X and Y for each one. I'd like to get a list of the regression intercepts and slopes for lm(Y~X) within each group. The intercepts and slopes don't need to be in the same dataframe.
Any suggestions? R beginner here, so simplicity would be great!
|
$X = AS$ where $A$ is my mixing matrix and each column of $S$ represents my sources. $X$ is the data I observe.
If the columns of $S$ are independent and Gaussian, will the components of PCA be extremely similar to that of ICA? Is this the only requirement for the two methods to coincide?
Can someone provide an examp... |
I apologize ahead of time if this a trivial question. I am building probability models for games - and in order to test the game code, I am comparing the results of large iterations of games with the original probability models. Specifically, I am calculating Standard Deviation, Skewness and Excess Kurtosis and using... |
I have some multilevel data with a group variable (groups 1-100). Some of my other variables are within-group means, hence they have the same value repeated for every individual within group i. I'd like to reshape the data so that each group has only one line (instead of one for every individual within the group) so I ... |
I refer to this link for calculating the sample size needed based on the width confidence interval needed, and the guessed proportion. I realize that it is use the "asymptotic" method when calculating the sample. Having know that the "wilson" method is a better way for estimating the CI for proportion[a]. I wonder if t... |
Interviewstreet had their second CodeSprint in January that included the question below. The programmatic answer is posted but doesn't include a statistical explanation.
(You can see the original problem and posted solution by signing in to the Interviewstreet website with Google creds and then going to the Coin Tosse... |
I'm working on a Bayesian Regression problem where I would like to estimate the beta coefficients subject to this constraint (penalty):
$\sum|\beta_i|<C$ or similarly $\sum \beta_i^2<C$
Which is basically a Lasso or L2 Penalty.
Now, if I understand correctly, we constrain the coefficients through the prior in Bayesian ... |
I have two samples, one of size 52, and one of size 31, that are obtained at different times. I'd like to get a 95% bootstrap confidence interval for the difference between the means of the populations that these samples represent. I've been trying to use the "boot" package in R, and I'm getting an error that I can't f... |
I've implemented an application that collects some relevant data about certain topics, so for each topic I get a list of strings. I want to make a test to see if the data makes sense.
I thought of making a survey, given the same list items (unsorted) and ask the survey takers to sort them. Then I would see how close th... |
Suppose I have survival data with more than one row per subject, because I have splitted the follow-up time of each subject into pieces (maybe because I have one or more time-varying variables or maybe just because I want to fit a Poisson model with a non-constant hazard over time).
Do I have to use the robust varianc... |
Im quite new to the world of statistics, and only just finished work on my first (successful) attempt to calculate mutual information scores.
Now lets say that for the column pairs AB, BC, CD and DE I have mutual information scores 0.1111, 0,9999, 1.23 and 1.5.
I need to use these values to accertain which of column pa... |
I have project where I'm given a set of times between a certain event and then I have to estimate the parameters for the ditribution function with the best fit using R, similar to what EasyFit does.
Unfortunately, I'm fairly new to R and statistics in general so I'm having a hard time getting off the ground. I'm attemp... |
My question builds on a previous post on outlier detection in generic time series, and specifically on the answer provided by the always great Rob H.
I work for a small-sized manufacturing company that currently handles the issue, i.e. detecting outliers in sales data time series, employing a (dubious) automated off-th... |
A neural network applied to time series needs to have the number of input nodes defined. Each input is applied to a time point previous to the current point being predicted. If $D$ is the number of past time points taken, how is this number determined? Can the autocorrelation function be used for the lag correlation pl... |
I am undergraduate student and I have a problem in my research. Recently, my supervisor told me that if using secondary data no need to perform normality test, why? It is got any citation or previous research prove this?
|
Is there any situation in which
$$\text{var}(d_t-f_t)=\text{var}(d_t)+\text{var}(f_t)-\text{cov}(d_t,f_t)$$
can be used instead of
$$\text{var}(dt-ft)=\text{var}(d_t)+\text{var}(f_t)-2\text{cov}(d_t,f_t)$$
where $d_t$ is a times series and $f_t$ is it's forecast.
thank you.
|
Are there any methods to correct bias in Cox proportional hazard model caused by non-randomly selected sample (something like Heckman's correction)?
Background:
Lets say the situation looks as follows:
- During first two years all clients are accepted.
- After those two years a Cox PH model is build. Model predicts how... |
I've got a dataset that looks like this:
id start end score1 score2
[...]
LmjF.31 280000 290000 . .
LmjF.31 290000 300000 . 2686
LmjF.31 300000 310000 . .
LmjF.31 310000 320000 . 74
LmjF.31 320000 330000 . 1897
LmjF.31 330000 340000 . 4116
LmjF.31 340000 ... |
Background
I'm working on a new effort estimation model (dissertation work) which involves software engineers organizing tasks (rank ordering) in order of increasing effort based solely on their understanding of the requirements. For example, writing a function to calculate an average should require less effort than wr... |
I am developing an online assessment system and I need to calibrate the bank of questions but I do not have enough people to implement a pilot test. That is why I decided to simulate the responses of the question bank. I will use the Rasch model for the development of a computer adaptive test (CAT); I have only questio... |
I am measuring the X, Y, Z variables of i subjects in k states, and for each subject and state i am taking j measurements. What is the proper way to test for differences between the k states?
It seems likes a one way repeated measure ANOVA problem, however how should I deal with the fact that in each subject and within... |
Here is my experiment:
I am using the findPeaks function in the quantmod package:
I want to detect "local" peaks within a tolerance 5, i.e. the first locations after the time series drops from the local peaks by 5:
aa=100:1
bb=sin(aa/3)
cc=aa*bb
plot(cc, type="l")
p=findPeaks(cc, 5)
points(p, cc[p])
p
The output is
[1... |
Suppose we have a simple regression model $y=\beta_0+\beta_1x+u$ under Gauss-Markov assumptions, and $u$ has a uniform distribution on $[0,1]$. Find sampling distribution of the $t_{\beta_1}$-statistic. $t_{\hat{\beta_1}}=\frac{\hat{\beta_1}}{se(\hat{\beta_1})}$, where $se(\hat{\beta_1})=\frac{[(\sum\limits_{i=1}^n{\ha... |
What is a main difference between RBF neural networks and SVM with a RBF kernel, from a practical point of view?
|
My problem described in buckets and balls (this is stats after all)...
I have 1 million buckets.
In each bucket I have some number of balls.
I want to model this system so that I have the expected number of balls for a bucket. (I expect my distrubtion of balls per bucket to be "gaussian" shaped)
Since my counts are int... |
I use lme4 in R to fit the mixed model
lmer(value~status+(1|experiment)))
where value is continuous, status and experiment are factors, and I get
Linear mixed model fit by REML
Formula: value ~ status + (1 | experiment)
AIC BIC logLik deviance REMLdev
29.1 46.98 -9.548 5.911 19.1
Random effects:
Groups ... |
We are interested in fitting a multiple logistic regression model using data obtained from a national survey of children with special health care needs. The data has an accompanying weight variable intended to standardize children to the national population in which we intend to make inference. This weight variable doe... |
I have two lists containing X/Y values which are used to plot points on a graph. The X-values are always sequential (1, 2, 3, 4...) but the Y values can vary.
For example:
var x = new List<int>(new[] {0, 1, 2, 3, 4, 5, 6, 7});
var y = new List<int>(new[] {0, 3, 7, 12, 14, 15, 17, 19});
var avgY = // What goes here?
Wi... |
Assume ${{X}_{1}}$, ${{X}_{2}}$, ${{X}_{3}}$,...,${{X}_{n}}$ are i.i.d. samples from distribution with density f, and cdf F.
Let V=min( ${{X}_{1}}$, ${{X}_{2}}$, ${{X}_{3}}$,...,${{X}_{n}}$)
To find the minimum $${B}_{v}={\{V\ge{v}\}}=\{{X}_{1}\ge{v}\}\cap\{{X}_{2}\ge{v}\}\cap...\cap\{{X}_{n}\ge{v}\}$$
So, $$P(V\ge{v}... |
I'm working on a data set and linear regression is beating a randomforest (the metric is weighted mean absolute error - I have a list of weights and each difference $|\text{predicted} - \text{actual}|$ is multiplied by that rows weight (which is a $\sqrt{\text{time}}$ so longer time between observations are charged a h... |
Suppose i have a little over 20.000 monthly time series spanning from Jan'05 to Dec'11.
Each of these representing global sales data for a different product. What if, instead of computing forecasts for each and every one of them, I wanted to focus only on a small number of products that "actually matter"?
I could rank ... |
I'm doing a research module for my Computer Science degree, and for my topic, I have collected over 500,000 tweets using the Twitter Streaming API, using a ruby script to store them in a Mongo database (BSON/JSON). I started recording the tweets on Tuesday 7th Feb, and stopped the following Tuesday, so there is a week'... |
I want to start working on data-mining by parsing text. It seems like the best place to start is by processing n-grams out of text to try sentiment analysis.
Muffins are fine, I wouldn't say I like them though.
However, I'm curious to know if I should include punctuation or not. (I plan on starting with 3-grams and wo... |
I have a model that is fitted with glm and I want to be able to calculate the response of this model when I specify the independent variables, while simulating the error terms. For example, if my formula is y~x1*x2, then this corresponds to:
$y_{i} = \mu + \beta_{1} x_{1i} + \beta_{2} x_{2i} + \beta_{3} x_{1i} x_{2i} ... |
I just read an interesting article on how Target used purchase behavior as a predictor to whether they were pregnant or not. Here's the link.
Could someone explain how Target build the predictive model, or their best guess as to the process?
Update
The original article is in New York Times.
|
Suppose I observe a random variable $x$ drawn from a non-central t- or F- distribution, and would like to perform inference on the non-centrality parameter. How would a Bayesian approach this problem? Are there known conjugate priors for these?
For the t-distribution I have seen some reference to LeCoutre's 'lambda-pr... |
Possible Duplicate:
Dynamic recommender systems
A Recommender System would measure the correlation between ratings of different users and yield recommendations for a given user about the items which may be of interest to him.
However, tastes change over time so old ratings might not reflect current preferences and v... |
Just trying to see if my reasoning is correct....
If the probability that next saturday will rain is 0.25 and the probability that next sunday will rain is 0.25, what is the probability that during the weekend will rain?
Assuming that A and B are independent events,
P(A∪B)=P(A)+P(B)-P(A∩B)
and
P(A∩B)=P(A)*P(B)
therefor... |
So I'm running some experiments using long-short term memory networks for temporal sequence regression, and one of the sequences I have to use is generated using the mackey-glass differential equation. To make it comparable to another temporal sequence prediction algorithm, we have to use the same protocol as [this oth... |
I have a novice background in time series (some ARIMA estimation/forecasting) and am facing a problem I don't fully understand. Any help would be greatly appreciated.
I am analyzing multiple time series, all over the same time interval and all of the same frequency, all describing a similar type of data. Each series i... |
More of a general question. I'm running an rbf SVM for predictive modeling. I think my current program definitely needs a bit of a speed up. I use scikit learn with a coarse to fine grid search + cross validation.
Each SVM run takes around a minute, but with all the iterations, I'm still finding it too slow. Assuming ... |
How to define the value of bandwidth when we have a vector where all the values is the same? In this case, IQR and sample variation are both equal zero and Silverman's rule also result in zero.
Using R, we have for $\vec{v} = (1,1)$ the bandwidth of 0.7835
density(c(1,1))$bw
and for $\vec{v} = (10,10)$, the value 7.8... |
Can someone explain my Cox model to me in plain English?
I fitted the following Cox regression model to all of my data using the cph function. My data are saved in an object called Data. The variables w, x, and y are continuous; z is a factor of two levels. Time is measured in months. Some of my patients are missing d... |
I am not sure in the terminology, so I will simply try to explain the situation that I would like to model as I see it. Suppose there is a set of random variables. The variables are correlated in such a way that they deviate from their expected values into the same direction all together. By this I mean that they can b... |
In logistic regression with an N of 40,000, purchase decision is unrelated to price. However, with certain demographic variables controlled, price can show a positive coefficient of meaningful strength. (Searches for 2-, 3-, and 4-way interactions involving price have yielded nothing.)
The goal here is to maximize t... |
I have several populations where I have morphology and diet for each individual. I am interested in the correlation between diet and morphological distances. However the number of individuals in each population ranges from 22 to 80 individuals. I have looked at the correlation diet-morphology for each population and (n... |
Quantile for a single variable is easy to implement in R. However, it is not an easy task to quantile for multivariate data. There are several papers have been proposed to quantile for multivariate data such as Chaudhuri, P (1996), On a geometric notion of quantiles for multivariate data, Journal of the American Statis... |
I estimated the breakpoint for a piecewise linear model (one intercept, two slopes that meet at the breakpoint) by minimizing the deviance using an optimizer (optim in R). I noticed that the estimate was near 2.0, 4.0, and 6.0, depending on the initial conditions, indicating there were local optima. So I used simulated... |
To do one clustering analysis, the model that I developed contains some 30 variables. I need to run this clustering for some 2-3 million data points. I need to know whether number of variables that I intend to use (30) is just too many? Would my result be impacted 'coz of large number of variables?
Also there would be ... |
I have two different implementations of ridge in MATLAB. One is simply
$\mathbf x = (\mathbf{A}'\mathbf{A}+\mathbf{I}\lambda)^{-1}\mathbf{A}'\mathbf b$
(as seen on Wikipedia's ridge regression page), with $\mathbf{I}$ being the identity matrix of size columns($\mathbf{A}$) $\times$ columns($\mathbf{A}$), and
I'm sim... |
This is something that I've wondered about mostly in connection with weather forecasting, but I would like to ask the general question because it comes up from time to time in other contexts.
Suppose I have a process, denoted $F$, which, given some initial state $x$, produces an outcome $y$ from among a discrete set of... |
I'm working with automating some data-retrieval, and now need to do some verification of the results. The system has automatically flagged 6% of the records, and I would like to determine a reasonable size of the remaining records to be manually verified, which will give me some assurance that other errors, if present... |
This was also asked at Computational Science.
I am trying to compute a Bayesian estimate of some coefficients for an autoregression, with 11 data samples: $$ Y_{i} = \mu + \alpha\cdot{}Y_{i-1} + \epsilon_{i} $$
where $\epsilon_{i}$ is Gaussian with mean 0 and variance $\sigma_{e}^{2}$
The prior distribution on the vect... |
I have 4 dependent categorical variables and 11 independent variables.im not been able to write the commands in R using the CRAN's mvtnorm.
Can anyone help me with that?
|
A colleague discussed about a concept of similarity between two different entities line and a set of points. My first guess for solution was considering distances squared ($d^2$) as in LS. So for the following demonstration in which the black line is fitted by means of Least Squares method is more similar to the points... |
I'm currently trying to play around with NLTK and scikits-learn for text clustering news articles.
How do I extend the models to add the scaling of features from a document (I'm doing some preprocessing on the text articles) so I can experiment by weighting ?
I'm starting from this outline of document clustering:
http... |
Consider the simple regression model $y=\beta_0+\beta_1x+u$, where $\text{corr}(x,u)=1$ and all random variables have normal distributions. Is it possible to provide asymptotically consistent estimates for $\beta_1$?
Since $corr(x,u)=1$, we can write $u=ax+b$ and substitute it to get $y=\beta_0+b+(\beta_1+a)x$. So our... |
I have read that the distribution for the random effects estimator in lme4 is highly skewed and for this reason standard errors are not reported. I wonder if anyone can provide a reference for this ? I have access to the book by Bates and Pinherio, but not Raudenbush and Bryk. A published paper would also be fine. Than... |
I have 168 rows of patient data: 104 controls and 64 cases. I want to know if albumin status (low or high) is related to case/control status. I made a table using R:
> table(Albumin, Status, useNA = "ifany")
Albumin Control Case
Low 51 16
High 39 32
<NA> 14 16
As you can see, I... |
Some attribute $x$ of 17 individuals was recorded repeatedly on 6 time points using a Likert scale with 7 distractors. Which statistical test(s) can I apply to check whether the changes along the 6 time points were significant?
set.seed( 123 )
x <- matrix( sample( 1:7, 17*6, repl=T ),
nrow = 17, byrow = TRUE,
dimn... |
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