instruction stringlengths 9 38.7k |
|---|
Suppose I run Multidimensional Scaling and I got the resulting plot. Can anybody suggest me how to interpret the plot. Please find one of my result below. Here I've 5 concepts which I run the MDS based on 10 variables. I'll be grateful if somebody can help me out.
Regards,
Ari
|
I am trying to tackle a problem which deals with the imputation of missing data from a panel data study(Not sure if I am using 'panel data study' correctly - as I learned it today.) I have total death count data for years 2003 to 2009, all the months, male & female, for 8 different districts and for 4 age groups.
The d... |
Consider the following model
$$
X \sim |\mathcal{N}(X;0,1)|
\qquad
Y|X \sim Q(Y;X)
$$
where I define $Q(Y=-x|X=x)$ with probability mass $\int_{-\infty}^{-x}\mathcal{N}(x;0,1)dx$, $Q(Y=+x|X=x)$ with probability mass $1-\int_{x}^{\infty}\mathcal{N}(x;0,1)dx$, and the density of $Q(Y|X=x)$ to be one of a truncated Normal... |
I would like to generate datasets which has 3 treatment groups: A, B, and C based on 3 covariates: $x_{1}$, $x_{2}$ and $x_{3}$. The $x_{1}$ and $x_{2}$ are standard normally distributed and $x_{3}$ is Bernoulli (0.5) distributed. Besides these, assume risk difference between A & B = -0.36, A & C = -0.26 and B & C = 0.... |
I am facing a problem of learning clusters from a pairwise dissimilarity matrix. The measures i try are not metrics(not symmetric,no triangular equality), like KL-divergence for example.
Are there Clustering methods i can use to find clusters from these kinds of matrices?
If i have labels available, what kind of clust... |
Possible Duplicate:
Working with Likert scales in SPSS
I have a data sample of which recorded individual's perception on whether a specific option is viable or not. The data was recorded on a lickert scale of 1 - 5. So basically, I'm looking to say that the "general perception of the sample is ____"
The mean = 2.83 ... |
I always believed that time should not be used as a predictor in regressions (incl. gam's) because, then, one would simply "describe" the trend itself. If the aim of a study is to find environmental parameters like temperature etc. that explain the variance in, let´s say, activity of an animal, then I wonder, how can ... |
I'm a novice who is going to start reading about data mining. I have basic knowledge of AI and statistics. Since many say that machine learning also plays an important role in data mining, is it necessary to read about machine learning before I could go on with data mining?
|
Consider the following two problems:
We want to do linear regression, where we know that the true model is actually linear. In the general case, linear regression includes an offset. However, we know, using prior knowledge, that the true model actually has offset 0. So clearly, it is better to fit the model while cons... |
I have a variable which decays very quickly (exponentially). I want to transform it in a way it maintains "exponentially decaying" property but which will allow me to control the "speed" of a decay.
original <- c(100, 80, 70, 65, 64, 63, 63, 63, 63, 62, 62, 61);
plot(original);
target <- c(100, 90, 70, 60, 65, 64, 64, ... |
Imagine that you want to assess the compressibility of a large document very fast. You could randomly pick a subsequence, try to compress it. This can serve as a prediction for the overall compressibility of the document. But how big should your sample be?
We have come up with the following strategy:
Pick an arbitrar... |
I'm currently in the planning stages of an experiment that I hope will detect a 0.155% signal variation (relative magnitude) within a reasonable time frame (less than 6 months ideally). I've calculated the rate of (usable) data will be around 68 events per day, though it should be stressed this is a random variable. No... |
My understanding is that $R^2$ cannot be negative as it is the square of R. However I ran a simple linear regression in SPSS with a single independent variable and a dependent variable. My SPSS output give me a negative value for $R^2$. If I was to calculate this by hand from R then $R^2$ would be
positive. What has S... |
I have three sets of time-series data I am looking to compare. They have been taken on 3 separate periods of about 12 days. They are the average, maximum and minimum of head counts taken in a college library during finals weeks. I have had to do mean, max and min because the hourly head counts were not continuous (see ... |
I am not sure whether this is the right place to ask this question, but any possible answer will help.
I want to apply some form of template matching on these set of pictures.
This is the template picture:
This is the picture in which I want to search for the template picture and the black rectangle, frame the templat... |
I have a data set that has 10k documents, each of which is mapped to one and only one of 4k categories. This forms my training set.
My requirement is that when a new, unseen document comes in, I need to be able to identify all the categories (from among the 4k categories) to which it belongs.
What is the best way to ... |
I'm preparing a presentation about parallel statistics. I plan to illustrate the formulas for distributed computation of the mean and variance with examples involving center of gravity and moment of inertia. I'm wondering if there is a physical interpretation of the third or higher central moments that I can use to hel... |
I've got a series of statistics computed on different populations of cells, where each population contains a different genetic deletion.
The measurements I have for each population involve GFP intensity: median intensity, mean intensity, median absolute deviation of intensity, max intensity and min intensity.
I'd like... |
I'm trying to visualize a matrix of 3 datasets.* For the sake of example, let's say I have a list of hats, coats and shoes, and I want to display a 2D grid/visualization of each possible combination.
Is it even possible without turning it into a 5x25 grid?
I had a look at this thread:
Visualizing multi-dimensional data... |
In R, the function skewness from package moments allows one to calculate the skewness of the distribution from a given sample. Does anybody know if there is a ready-to-use function to calculate the skewness of the distribution from a given histogram?
|
I am using Silhouette width to compute the best value for k in k-means. As I am performing document clustering, I am calculating the values of a and b as follows in Python:
a = distance(data[index], centroids[clusters[index]], metric=metric, p=p)
b = min([distance(data[index], c) for i,c in enumerate(centroids) if i !=... |
I'm pretty lost at how to approach this, and particularly with regards to the terminology; so please feel free to point to resources, fix my question name, etc. Thanks.
I used R back in college, I've got Orange installed. I've heard of MiniTab. I've got Excel installed. I've got access to SQL Server 2008 w/ Analysis Se... |
I'm reading Hayashi's "Econometrics", and in Chapter 2, page 101 he discusses the following white noise process:
I understand the calculations for the expected mean and variance, but I can't understand why the covariance would be 0 for $i\neq j$.
Since $E(z_i)=0$, the expression for the covariance would be reduced to... |
What are some good, established methods for estimating the probability density function (denoted $f(x)$ from here on) of a continuous distribution, given a sample of points $x_1, \ldots, x_n$ drawn from it? I primarily need the PDF for plotting purposes.
The naive approach would be using a histogram, i.e. counting how... |
Im using gradient-descent-based algorithm for my problem where
new_value = old_value - Step_size*Gradient
For exit criteria, im determining the change in fn value between iteration i.e.,
if (old_Objective_fn_value - new_Objective_fn_value) <=0.001 exist otherwise continue.
For different Step_size, the algorithm meets ... |
Suppose $(\mathscr{X,B,P})$ is a statistical model and $(\mathscr{X,B,P})^n$ is the corresponding model for sampling with replacement. My text book states that its incompleteness allows multiple unbiased estimators, where problems such as which estimator is better arises. But I don't understand why the model is incompl... |
As the R very beginner I'd like to ask if anyone could help me with the following problem?
library(foreign)
reg1 <- read.spss("URL of the spss file")
library(nlme)
model1 <- gls(v1 ~ x1 + x2 + x3 + x4 + x5 + x6, correlation=corARMA(p=1), data=reg1)
Error in eval(expr, envir, enclos) : object 'v1' not found
All the var... |
I keep reading that people are estimating the Google+ population based on statistical estimates:
My model is simple. I start with US Census Bureau data about surname popularity in the U.S., and compare it to the number of Google+ users with each surname. I split the U.S. users from the non-U.S. users. By using a sampl... |
Are you aware of any examples of election forensics in practice? Or at least any applied research on real large-scale datasets (e.g. govermental elections)? Thanks.
|
I've got an easy question concerning residual analysis. So when I compute a QQ-Plot with standardized residuals $\widehat{d}$ on the y-axis and I observe normal distributed standardized residuals, why can I assume that the error term $u$ is normal distributed? I'd think that if $\widehat{d}$ looks normal distributed I ... |
I don't have a strong background in statistics, so forgive me if I'm making very elementary mistakes here or if this question is too simplistic.
I am in a club with ~80 members, and every week, 10 members are selected to win a prize.
No member can be selected to win a prize twice in a row, but other than that, anything... |
I'm puzzled: what does a Greek $\Gamma$ mean in statistics? For example, here http://en.wikipedia.org/wiki/Weibull_distribution in the definition of the mean.
|
I am currently trying to simulate values of a $N$-dimensional random variable $X$ that has a multivariate normal distribution with mean vector $\mu = (\mu_1,...,\mu_N)^T$ and covariance matrix $S$.
I am hoping to use a procedure similar to the inverse CDF method, meaning that I want to first generate a $N$-dimensional ... |
There is a set of daily measurements. Time and measured values are both discrete. I want to find out whether measured values depend on the day the measurement was taken, or whether measurements are completely random.
In other words, I want to find out if it is possible to predict measured values of a certain day or not... |
While having chronically data of population growth (registered users of a site), I want to compute a function that approximates future growth, based on past data. Also, what we ll be the distribution of that function? What is the distribution of interarrivals between consecutive registrations.
|
When estimating a group level interaction I get the following error:
model <-lmer(rtln ~ + ifIncongruent + gender + ifIncongruent:gender + (1|subj:ifIncongruent), data=dataset)
Error in validObject(.Object) :
invalid class "mer" object: Slot Zt must by dims['q'] by dims['n']*dims['s']
In addition: Warning messages... |
I want to process automatically-segmented microscopy images to detect faulty images and/or faulty segmentations, as a part of a high-throughput imaging pipeline. There's a host of parameters that can be computed for each raw image and segmentation, and that become "extreme" when the image is defective. For example, a... |
To get started on statistical analysis -- where would you recommend I go to learn?
|
I'm looking to understand this from a managerial perspective. For example if I was explaining linear regression I would say it is a line of best fit through some data points and it can be used to predict a "y" value for some given value of "x". Is there an analogous explanation for VAR? I do not have a strong backgroun... |
This has been inside my mind for at least a few hours. I was trying to find an optimal k for the output from the k-means algorithm (with a cosine similarity metric) so I ended up plotting the distortion as a function of the number of clusters. My dataset is a collection of 800 documents in a 600-dimensional space.
From... |
Can anyone recommend any machine learning techniques for time series estimation?
I have a series of times $t_{1}...t_{n}$, each having a set of associated features $f_{1}...f_{m}$, and a value $x$.
I want to estimate the value of $x$ for the next time in the series given a set of corresponding features $f_{1}...f_{n}... |
In my logistic regression model, I have one independent variable that has a B value of 0, p = 0.006 and exp(B) = 1. Goodness-of-fit measures indicate that the model is acceptably "good".
Intuitively, I would imagine a significant variable to have a non-zero coefficient and some effect. Statistically though, I am not su... |
Maybe this is a naive question so do not blame me. I wonder if biclustering is equivalent to perform a clustering then a variable selection (eventually followed by a new clustering)?
Do these approaches produce different results?
|
Is there a way to run the sem function (R sem package) by using WLS method?
Furthermore I have a very small data set (20 observations), can I overcome this problem by using a bootstrapping technique?
|
I am working with a time series of meteorological data and want to extract just the summer months. The data frame looks like this:
FECHA;H_SOLAR;DIR_M;DIR_S;VEL_M;VEL_S;VEL_X;U;V;TEMP_M;HR;BAT;PRECIP;RAD;UVA;UVB;FOG;GRID;
00/01/01;23:50:00;203.5;6.6;2.0;0.5;-99.9;-99.9;-99.9;6.0;-99.9;9.0;-99.9;-99.9;-99.9;-99.9;-99.9;... |
I would like to stay away from finance and economic examples since they are too abstract for me to understand. Are there any "real world" examples for example healthcare, exam marks, environmental science and so on? From a managerial perspective I would like a basic understanding of how VAR could potentially be used ... |
An example is here: http://www.reddit.com/r/askscience/comments/ine4x/regarding_the_recent_lapse_of_global_warming_in/c2554al
I'm sure it's related to robust statistics. But I'm sure that there's a label more specific than that.
==
Okay, so I tried to run regression analyses on global warming datasets over the last 10 ... |
Let's say I have a simple 2x2 factorial experiment that I want to do ANOVA on. Like this, for example:
d <- data.frame(a=factor(sample(c('a1','a2'), 100, rep=T)),
b=factor(sample(c('b1','b2'), 100, rep=T)));
d$y <- as.numeric(d$a)*rnorm(100, mean=.75, sd=1) +
as.numeric(d$b)*rnorm(100, mean=1... |
My question is:
Is there a way to either force Anova() to somehow analyze gls objects (which internally are almost identical to lme objects), or force Anova() to honor the test.statistics='F' argument, or at least do a valid type-II sum of squares by hand on an lme and a gls object?
Why:
I'm trying to get Anova outp... |
I've run into a simple problem - but no idea how to access it correctly.
I've 85 people asked concerning their social network; first example: how many friends do you have. Second, what gender is each of this friend. Then I do a table which displays the average number of female friends and the average number of male fri... |
Looking for help to create a model for my data gathered from a reciprocal transplant experiment: I have 2 populations of fish (A and B) and 2 temperature regimes (warm and cold) that were crossed with each other (= 4 treatment groups- A:warm, A:cold, B:warm, B:cold). Each treatment group consists of two replicate ta... |
I am reading an overview of AdaBoost written by Schapire, which calculates the upper bound of the training error in Eq. (5), section 3. In fact, it states that
$$\prod_{t}Z_t=\prod_{t}\left[2\sqrt{\epsilon_t(1-\epsilon_t)}\right]$$
with
$$
\begin{align}
Z_t=&\sum_{i}D_t(i)\exp(-\alpha_ty_ih_t(x_i))\\
\alpha_t=&\frac... |
I am reading a text, "Mathematical Statistics and Data Analysis" by John Rice. We are concerned with approximating the expected value and variance of the random variable $Y$. We are able to calculate the expected value and variance of the random variable $X$ and we know the relation $Y = g(X)$. So, it's possible to app... |
I'm looking to use n-fold cross validation for selecting meta-parameters for fitting a model to a dataset. However, dropping observations entirely from the learning-set while fitting the model to each of the folds may create problems for the model fitting.
I was wondering whether it would be valid to perform the cross-... |
A tutorial on AdaBoost suggests that AdaBoost can be applied to a continuum of classifiers (at the bottom of the first page).
Does it mean to simply discretize the classifiers, for example, which are parameterized by one or two real number, or refer to a generalized version of AdaBoost theory, which may be capable of c... |
I have (what I will term, for lack of a better word) a random walk that has a particular property: it tends to be right of the origin some fraction k of the time and left 1-k of the time (and on the origin a negligible fraction). So although the probabilities of going up or down are close to 1/2, there is a central te... |
I have run several Chi-square tests and want a measure of effect size. I have some 1x2 tables, 1x4 tables, 4x9, and 3x4 tables of frequency data.
What measure of effect size can I use on these rectangular frequency tables, if each cell has a different expected frequency?
(I would like to use something like Cramer's V,... |
I'm just very curious about the discovery process behind the autocorrelation function.
When was it invented?
Was it independently invented multiple times, for example?
What was the motivation for it?
|
First off let me say that I had one stats course in engineering school 38 years ago. So I'm flying blind here.
I've got the results of what are essentially 18 separate diagnostic tests for a disease. Each test is binary -- yes/no, with no threshold that can be adjusted to "tune" the test. For each test I have what i... |
In a previous question I asked about the history of auto-correlation
In this question I'm interested in the discovery process behind cross-correlation.
When was it invented?
Was it independently invented multiple times?
What motivated its invention?
|
I am looking for an optimization routine that can optimize a non-linear objective function with integer constraints. NuOPT for S-Plus, CPLEX, or Matlab include powerful optimization packages for these kinds of optimizations?
Is there any similar kind of package for R? Or is there an optimization procedure (perhaps gene... |
I want to learn data mining. Are there any free video lectures out there which explain the process of data mining in depth?
|
I'm trying to analyse an experiment I performed. I executed 9 tests measurements, at two different settings (A and B); I expect it to be normal distributed. I had the following hypotheses:
$H_0:\; \mu_A = \mu_B$
$H_1:\; \mu_A \neq \mu_B$
I got the following results for my measurements
A: n=9, mean = 1.66, sd = 1.12... |
I'm testing two different settings (say 'A' and 'B') for a machine. From physical arguments, I know that $\mu_B >= \mu_A$. If really $\mu_B < \mu_A$, there's something fundamentally wrong with my model. So there are three options:
$H_0: \mu_B = \mu_A$ (setting doesn't make a difference)
$H_1: \mu_B > \mu_A$ (setting m... |
I'm trying to apply the Kolmogorov-Smirnov test for goodness-of-fit to a dataset. I have a large set of values, and would like to know whether it fits a Poisson distribution with given $\lambda$.
As I am using Java to generate the dataset, I have found a Java class which is supposed to calculate what I want - it's call... |
I would like to understand the topic conceptually rather than through equations
|
I have to do some studies on time series, which involve computing the covariance matrix. However, my time series span on different time intervals and their intersection is too short to provide me a good estimator.
I guess I have to remove some time series but I don't know how to select the ones to keep.
I can come up... |
Could someone explain me which is the null hypothesis of the energy test of multivariate normality (R package energy)? By using this test I obtained a very different p-value from that I obtained with mshapiro.test.
|
I am carrying out a zero-inflated negative binomial GLM on some insect count data in R. My problem is how to get R to read my species data as one stacked column so as to preserve the zero inflation. If I subtotal and import it into R as a single row titled Abundance, I loose the zeros and the model doesn't work. Alread... |
I have a data set which is a set of continuous distances from some origin. I originally modeled this as a negative binomial distribution by rounding the data and using it as an input in the Matlab function, nbinfit:
nbReg = nbinfit(round(data));
Using the output from nbinfit, I created the following CDF:
Here are the... |
I was wondering, in relation to model selection for some count data I am looking at using poisson GLMs, would a high residual deviance (measure of dispersion) warrant switching to a quasi-poisson model before or after dropping unimportant explanatory variables?
|
I'm currently writing a program to learn a TAN (Tree-Augmented Bayesian network) classifier from data, and I have almost finished it. I use the algorithm described in Friedman's paper 'Bayesian Network Classifiers', and for continuous variables, I assume a Gaussian distribution. I have tested my program on some dataset... |
I have a time course experiment that follows 8 treatment groups of 12 fish for 24 hours with observations made at 5 second intervals. Among the measurements made is how far each fish travels (in mm) between observations. The 24 hours are divided into 1 dark period and 1 light period.
Here is a plot of the movements o... |
I'm trying to fit a line+exponential curve to some data. As a start, I tried to do this on some artificial data. The function is:
$$y=a+b\cdot r^{(x-m)}+c\cdot x$$
It is effectively an exponential curve with a linear section, as well as an additional horizontal shift parameter (m). However, when I use R's nls() functio... |
Suppose you have a data set $Y_{1}, ..., Y_{n}$ from a continuous distribution with density $p(y)$ supported on $[0,1]$ that is not known, but $n$ is pretty large so a kernel density (for example) estimate, $\hat{p}(y)$, is pretty accurate. For a particular application I need to transform the observed data to a finite ... |
Suppose I want to build a model to predict some kind of ratio or percentage. For example, let's say I want to predict the number of boys vs. girls who will attend a party, and features of the party I can use in the model are things like amount of advertising for the party, size of the venue, whether there will be any a... |
I have a some data like the following explaining the presence of a relation between various entities (A,B,C,...) in my system at time t:
At T=1
A B C D . . .
A 0 2 1 0 . . .
B 2 0 1 3 . . .
C 2 1 0 2 . . .
D 0 3 2 0 . . .
. . . . . . . .
At T=2
A B C D
A 0 3 1 0 . . .
B 3 0 1 3 . . .
C 2 1 0 2 . . .
... |
I have a set of sequences of numbers, each sequence is independent from each other.
I'd like to know if, "in general", these sequences increase, decrease or remain the same.
What I have done so far is a fitted a linear model to each sequence, so that I can use the gradient to determine if the sequence is increasing or ... |
I am looking for data sets that contain individual sales data (e.g. the amounts paid by each customer at the cash register of a particular supermarket, or the amounts paid in 10,000 ebay transactions on a given day, or anything like that), without any aggregation. No covariates are required as I am principally interest... |
I'd like to convert a factor variable to a numeric one but as.numeric doesn't have the effect I expect.
Below I get summary statistics for the numeric version of the variable based on the original variable. The means keep counting up by 1... perhaps (he speculates) the levels of the factor have both names and number... |
I am very interested about the potential of statistical analysis for simulation/forecasting/function estimation, etc.
However, I don't know much about it and my mathematical knowledge is still quite limited -- I am a junior undergraduate student in software engineering.
I am looking for a book that would get me start... |
Background:
Generally, pooled time-series cross-sectional regressions utilize a strict factor model (i.e. require the covariance of residuals is zero). However, in time series such as security returns where strong comovements exist, the assumption that returns obey a strict factor model is easily rejected.
In an appro... |
Say you have N observations that are iid.
$$ \forall i, \quad p(X_i=x_i|\mu,\sigma,I) = \frac{1}{\sqrt{2\pi}\sigma}
\exp\left(-\frac{1}{2\sigma^2}(x_i-\mu)^2\right)$$
then
$$ p(x_1,\dots,x_N|\mu,\sigma,I) = \frac{1}{(\sqrt{2\pi}\sigma)^N}
\exp\left(-\frac{N}{2\sigma^2}[(\bar{x}-\mu)^2 + \bar{\sigma}^2]\right)$$
wi... |
I have two historical price lists with the following columns
data - price
Now i have to create the ratio between the prices of these lists:
list A: 01/01/2011 10.50
list B: 01/01/2011 23.89
I compare the date of the lists, if the day is the same I find the ratio, doing:
ratio = 10.50 / 23.89
Ok... I do this divis... |
I would like to quantify the amount of uncertainty in a given message, but the signal I work with is non-stationary and non-linear.
Is it possible to apply Shannon entropy for such signal?
|
I'd like to know if there is a boxplot variant adapted to Poisson distributed data (or possibly other distributions)?
With a Gaussian distribution, whiskers placed at L = Q1 - 1.5 IQR and U = Q3 + 1.5 IQR, the boxplot has the property that there will be roughly as many low outliers (points below L) as there are high ou... |
Recently I have learned about sequential analysis especially sequential probability ratio tests (after I have struggled a lot with cumulation of alpha - errrors). See also this question Sequential hypothesis testing in basic science.
My question is: What is the derviation or explanation of the tresholds of the stopping... |
Disclaimer: This is reposted from stackoverflow.
I am working on a research-oriented system of collaborating agents.
The agents perform many stochastic experiments (thousands per second), interacting with each other, in a complex high-dimension environment. Each experiment is reproducible and deterministic. The system ... |
I have this model:
model <- zelig(dv~(product*intervention), model = "negbin", data = data)
intervention has two levels: neutral(=0), treatment(=1)
product has two levels: product1(=0), product2(=1)
I build f_all to just have one factor with 4 groups for comparison analysis.
Thus I have 4 groups in f_all
1. product1-n... |
In performing an inverse transformation to correct for skewness/kurtosis in SPSS, it asks me to choose what "type" of inverse transformation and I have no idea what the differences between these transformations are. Is there any documentation on this or does anyone know the difference offhand? I couldn't find anything ... |
I know that for poisson regressions on count data that originate from different sampling "sizes", i.e. different volumes, areas etc, require an offset in order to adjust for the different sizes.
However, in Zuur et al. (2009) Mixed Effects Models in R in read on page 198 (ch.8.3.1.)
One option is to use the density ... |
So, here's the situation:
I have some simulation results, from a simulation driven by two parameters. One of these parameters has two settings, the other has four each was replicated ten times for a total of 80 sets of results.
Each simulation produces results for each of four groups. The progress of each group was mea... |
I'm having trouble understanding some of the formulas in this paper related to BIC calculation (Dan Pelleg and Andrew Moore, X-means: Extending K-means with Efficient Estimation of the Number of Clusters).
First the variance equation:
R - number of points
K - number of clusters
$\mu_i$ - centroid associated with ith p... |
In R I have a data frame f with headers a, b, c. Column c has factor data.
plot(f$c) does this
How can I limit the plot to the top 5 most frequently occurring factors of column c in descending order?
The following works just fine:
library(ggplot2)
data(diamonds) # clarity is a good categorical variable
with(diamonds,... |
I'm hoping someone can help straighten out a point of confusion for me. Say I want to test whether 2 sets of regression coefficients are significantly different from each other, with the following set up:
$y_i = \alpha + \beta x_i + \epsilon_i$, with 5 independent variables.
2 groups, with roughly equal sizes $n_1, n_... |
Given i.i.d. samples from a gaussian distribution $X_1,...,X_n \sim N(\mu,\sigma) $ and the M-estimator, $\mu_m = \underset{a}{\operatorname{argmin}} \sum\rho(|X_i-a|)$, what properties on $\rho$ are sufficient to guarantee $\mu_m \rightarrow \mu$ in probability? Is $\rho$ being strictly convex and strictly increasing... |
I have a vector
x = c("E1","E2","E4","E4","E5","E6","E10","I1","I2","I4","I12")
I need to sort that in a way the output should be
x = c("E1","I1","E2","I2","E4","E4","I4","E5","E6","E10","I12")
but when I use sort(x) it gives
c("E1","E10","E2","E4","E4","E5","E6","I1","I12","I2","I4")\
Is there anyway I could sort the... |
In James and Stein (1961) the authors consider the following loss function for an estimator $\hat{\Sigma}$ of the covariance matrix $\Sigma$ of a multivariate normal distribution:
$$L(\hat{\Sigma}) = tr[\hat{\Sigma}\Sigma^{-1}] - \log|\hat{\Sigma}\Sigma^{-1}| - p.$$
This loss function has since been referred to as `Ste... |
I'm a new statistics student :) I have some questions about linear regression, i'm using R to do some tests.
I have two simple lists, like:
> a <- c(1,2,3,4)
> b <- c(5,6,7,8)
then I do
> model <- lm(a ~ b)
the result (coefficient) is:
> coef(model)
(Intercept) b
-4 1
the "relationship... |
Can anyone tell me which R function to use for multiple imputation?
Also, what should I do to determine if the missing data are MAR or MCAR or not?
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.