instruction stringlengths 9 38.7k |
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I have the following set of data:
Time Counts Total Counts % Complete
1 2 2 2/10
2 0 2 2/10
3 4 6 6/10
4 3 9 9/10
5 1 10 10/10
In other words, after 1 minute went by, there ... |
Background: I am a biostatistician presently wrestling with a dataset of cellular expression rates. The study exposed a host of cells, collected in groups from various donors, to certain peptides. Cells either express certain biomarkers in response, or they don't. The response rates are then recorded for each donor-gro... |
I have started coding a Kalman filter in R. I am using dlmModreg to build an object of class dlm, which I am planning to use as my input to dlmFilter. But, I am stuck in the dlmModreg step itself. I am providing the parameters for dlmModreg as described in 1. This is my code
linear.reg <- lm(y.learn$hospitalizatio... |
I recently came across an example of using eviews to put non-linear/convex limits
on estimated coeficients on OLS.
I could track down a link to a forum describing how this is done (here)...
But I don't actually know anything more about how these models are estimated in practice. Has anyone a link to a paper/book/source... |
Is there an easy/standard way of sampling from a density estimated by kNN? I've searched online but I can't seem to find how to do this. Any links or methods pointing me in the right direction would be much appreciated. Just to clarify, I would want to be able to sample points not (necessarily) in my dataset from the e... |
In panel data analysis, I have used multi-level models with random/mixed effects to deal with auto-correlation issues (i.e., observations are clustered within individuals over time) with other parameters added to adjust for some specification of time and shocks of interest. ARMA/ARIMA seem designed to address similar i... |
I'm really new to statistics so sorry in advance if this question does not make sense.
Background:
I'm trying to learn about hidden Markov models and they seem interesting but I was wondering about the probabilities they use to generate their predictions. Most of the information I have read has probabilities already ab... |
What is the cleanest, easiest way to explain someone the concept of variance? What does it intuitively mean? If one is to explain this to their child how would one go about it?
It's a concept that I have difficulty in articulating - especially when relating variance to risk. I understand it mathematically and can expla... |
A simulation gives the population numbers for every species in the domain per frame. These vary over time and can be quite noisy, is there a way of analysing the data algorithmically without drawing a graph whether or not these values oscillate?
|
I am currently calculating reliability estimates for test-retest data.
My question is regarding the difference between standard error of measurement (SEM) versus minimum detectable change (MDC) when seeking to determine if there is a 'real' difference between two measurements.
Here is my thinking thus far:
Each measure... |
I have a gene expression data-set with log2-transformed expression values (no NAs) for 495 genes for 59 samples for which values of a continuous response variable (r) are also known (no NAs). I want to use leave-one-out cross validation to test if r of the test sample can be predicted from the sample's gene expression.... |
Testing the null hypothesis $H_0: \theta = 0$ against the alternative $H_1: \theta \neq 0$ is equivalent to constructing a confidence interval and checking whether or not zero belongs to it.
But what about the alternative $H_1: \theta > 0$. What is the "equivalent confidence interval?".
|
I am trying to classify two types of objects, which unfortunately have high-dimensional features with few samples. (230 features 12 samples from each group).
As a first step:
To reduce the dimension, I have tested three different approaches of PCA (each with slightly different parameters) and use the scores of the fi... |
Imagine we have two sets of data m1 and m2. m1 components have the dimension of [m^2/s] and m2 components are measured in [cm^2/s].
e.g.
m1={1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
m2={31, 32, 33, 34, 35, 36, 37, 38, 39, 40}
Assuming that B is the proportionality constant that is estimated as a straight line fitted to the po... |
How do you choose a model from among different models chosen by different methods (e.g. backwards or forwards selection)?
Also what is a parsimonious model?
|
All is in the title...
I know how to store the estimates but I don't know how to store their standard errors...
Thanks
> x <- runif(100)
> y <- 5 + 3 * x + rnorm(100, 0, 0.15)
> reg <- lm(y~x)
>
> summary(reg)
Call:
lm(formula = y ~ x)
Residuals:
Min 1Q Median 3Q Max
-0.32198 -0.12626 0.025... |
I would like to model the dimensions of the trade areas for a group of stores. I have geocoded sales data for each store, which I used to construct a convex hull using a GIS program. Essentially, I took the nearest 80 percent of sales for each store, and then snapped a rubber band around those points to get a trade are... |
I developed an algorithm that uses the chi-squared test to perform supervised discretization of a continuous variable. I described it in the paper "ChiD-A Chi-Squared Discretization Algorithm" published in the WUSS 2011 Proceedings available at http://www.wuss.org/proceedings11/
The stopping criterion is not very inte... |
Let's say I have a set of discrete, arbitrary variables sampled at continuous co-ordinates, e.g.
==================================
= x = y = Value =
==================================
= 4.1 = 3.4 = A =
= 4.6 = 7.9 = A =
= 4.7 = 8.1 = A =
= 2.1 = 5... |
Two common approaches for selecting correlated variables are significance tests and cross validation. What problem does each try to solve and when would I prefer one over the other?
|
Are assumptions for multiple linear regression basically the same as simple linear regression? One has to check for linearity for each of the continuous predictors versus the outcome variable? If there are categorical variables, one has to check the linearity between each of the continuous predictors with the outcome v... |
I have a question about SAS:
How do you get the parameter estimate for Mallows' Cp procedure in SAS?
|
A simulation gives the population numbers for every species in the domain per frame. These vary over time and can be quite noisy, for example we might have:
Species A: 1, 1, 2, 3, 4, 5, 5, 4, 3, 2, 1
Species B: 5, 4, 3, 3, 2, 2, 2, 1, 2, 3, 4
Fourier analysis gives:
Species A
[1] 31.0000000+0i -11.3435375+0i 0.72844... |
I KNOW what moments are and how to calculate them and how to use the moment generating function for getting higher order moments. Yes, I know the math.
Now that I need to get my statistics knowledge lubricated for work, I thought I might as well ask this question – it's been nagging me for about a few years and back in... |
I am faced with a problem, that I'm pretty sure is a statistical one, but me taking 1 course in probability followed by 1 course in statistics back in university did not prepare me to adequately face it. With that in mind, while a R-based sample code is always helpful and appreciated, what I'm really after is some dire... |
I couldn't find the scripts for Mixed-Effects Models in S and S-PLUS. The only place is http://stat.bell-labs.com which has code for first two chapters. I'd highly appreciate if someone point out the place to get the scripts for this book. Thanks in advance for your time and cooperation.
|
Is it enough to check residuals versus predicted values to see if the linearity assumption in multiple linear regression is satisfied?
Because for many predictors, you can't visualize the plot with the outcome variable.
|
I am using the library caret in R to test various modelling procedures.
The trainControl object allows one to specify a re-sampling method. The methods are described in the documentation section 2.3 and include: boot, boot632, cv, LOOCV, LGOCV, repeatedcv and oob. Although some of these are easy to infer, not all of th... |
Inspired by this question, and particular "Problem 3":
Posterior distributions are somewhat more difficult to incorporate into a meta-analysis, unless a frequentist, parametric description of the distribution has been provided.
I've been thinking a great deal recently about incorporating meta-analysis into a Bayesian... |
In a dataset with survival event, I calculated Harrell C-index from three different models.
Furthermore, I calculated the 95% C.I. for the three different models.
So the next question is to compare the discrimination ability of the three models.
Could anyone kindly suggest the method to compare the Harrell C-index?
|
Source | SS df MS Number of obs = 1797
-------------+------------------------------ F( 1, 1795) = 815.71
Model | 273.788275 1 273.788275 Prob > F = 0.0000
Residual | 602.478503 1795 .33564262 R-squared = 0.3124
----... |
Informal explanation: In the course of my research I've run into the following problem: I am observing a machine that outputs random numbers. Most (if not all) of these random numbers come from the Gaussian distribution $\mathcal{N}(0,\sigma_0^2)$. I know the value of the variance $\sigma_0^2$. However, some propor... |
I want to know the cross validation procedure to find the two parameters of elastic net presented by Zou and Hastie on the prostate dataset as example.
I can't improve the error rate lasso with k-fold when I use elastic net.
|
Can the terms LDA (Linear Discriminant Analysis) and GDA (Gaussian Discriminant Analysis) be used interchangeably?
Do they often refer to the same thing?
|
In ESL, Section 9.7, there is a paragraph stating that the computation time of a split in the growing of a classification (or regression) tree typically scales like $p N \log N$ where $p$ is the number of predictors and $N$ is the number of samples.
A naive approach results in a $pN^2$ scaling, and I haven't been able... |
I am fitting a 3-level model in Bugs. The data are in long format. The data consists of 885 Treatments in 1:3 COURSEs of treatment in 108 Patients (MRNs).
model{
for(DMRN in 1:NMRN) {
RMRN[DMRN] ~ dnorm(meanMRN[DMRN], TMRN)
meanMRN[DMRN] <- intercept
for(DCOURSE in SMRN[DMRN]:(SMRN[DMRN+1]-1)){
RCOURSE[DC... |
While checking to see whether two variables were correlated, I observed that applying Pearson correlation yielded numbers as low as 0.1 indicating no correlation. Is there anything I can do to strengthen this claim?
The dataset (subset because of the posting limits) I am looking at is this:
6162.178176 0.049820046
4675... |
I have started looking into robust methods of data analysis. In particular, robust regression methods for ANCOVA type models using the "lmRob" function from the "robust" library in R. I'm having a hard time finding what assumptions I need to satisfy in order to use this. I've read that they can be useful in situations ... |
I have done some AI projects involving inference, neural networks, etc., but I'm not sure what the right algorithm would be for this problem.
Say there is a set of pills, where each type is visually unique. So, for example, a pain reliever might be a red pill and an allergy medication might be a blue pill. One is seei... |
I hope this is the right place to post this, I considered posting it on skeptics, but I figure they'd just say the study was statistically wrong. I'm curious about the flip side of the question which is how to do it right.
On the website Quantified Self, the author posted the results of an experiment of some metric of ... |
Could anyone advise if the following makes sense:
I am dealing with an ordinary linear model with 4 predictors. I am in two minds whether to drop the least significant term. It's $p$-value is a little over 0.05. I have argued in favor of dropping it along these lines:
Multiplying the estimate of this term by (for examp... |
Let's say you have a large random sample of soccer players in Europe but you are only interested in what happens in Spain. Could you reduce your sample to players in Spain and still call it a random sample (but of a different population)?
If not, how would you call that subsample and which specific precautions should y... |
If I have two (Pearson) correlation coefficients between Variables A and B (for example .657 for males and .876 for females) and I want to test if there is a difference based on gender (as in this case), which of the following phrases should I use to describe this process?
Test for equality of the correlation coeffici... |
I need to generate random non-square matrices with $R$ rows and $C$ columns, elements randomly distributed with zero mean, and constrained such that the length ($L_2$ norm) of each row is $1$ and the length of each column is $\sqrt{\frac{R}{C}}$. Equivalently, the sum of square values is $1$ for each row and $\frac{R}{... |
I used a logistic regression model (glme4) to determine whether two different types of words (emotional vs. unemotional) are recognized more accurately (accurate=0, error=1) when shown in a particular color (green, red, blue). The logistic model shows a significant difference between red and blue with a coefficient of ... |
I have a stochastic model used to simulate time series of some process. I am interested in the effect of changing one parameter to a specific value and want to show the difference between the time series (say model A and model B) and some sort of simulation based confidence interval.
I have been simply running a bunch... |
I am currently in the process of making a poster presentation and would like some advice (or reference to advice) about some of the aspects of the graphic. For examples posters I am talking about see the supplementary material for the ASA Data Expo articles in Volume 20 Issue 2 of the Journal of Computational and Graph... |
I currently have an output function that roughly follows a $\chi^2$ distribution for random data with one degree of freedom. As a cursory analysis that has since proven mathematically unrigorous, this appeared to be bounded by $[0,1]$ on the x-axis, with a mode of 0, and a steep falloff such that my PDF offers highly s... |
I have 4.4 million observations, 160 binary features, and a binary response. Using rpart on Windows (64-bit, with the 64-bit R v2.13.0 build), I run out of memory on a machine with 64GB RAM. My memory limit seems reasonable:
> memory.limit()
[1] 61440
But on running rpart, I still receive this error after watching mem... |
10/16/2011 9:33:46 AM
10/16/2011 9:54:48 AM
The above are a few rows from my G$time column. I wanted to convert them to readable form when I graphed Y over Time, so I tried
Time<-strptime(G$Time,format="%D %H:$M:%S %r")
and then
Time<-strptime(G$Time,format="%m/%d/%y %H:$M:%S %r")
but it's not working. Can anyon... |
I have a continuous random variable $X$ (positive). I want to simulate its distribution with a discrete distribution and calculate $E[X]$ from that discrete distribution. So, the obvious approach is to divide the range of the random variable into step size of $h$; let the CDF values at the points $0,h,2h,\ldots,Nh$ be ... |
I got an example calculation for multiplicative model, which is shown as follows:
Quarter 1 2 3 4
Average 0.866 1.0005 1.403 0.660
--------------------------------------------------
Adjustment 0.0176 0.0176 0.0176 0.0176
Seasonal factor 0.884 1.018 1.421 ... |
I have a dataset of 13k horse races from four different tracks with an average of 11 runners per race. In all, there are 26k unique runners in the data. For each race, I know who came first, second, third, etc.
A horse's form is a record of significant events, including its performance in previous races. To be speci... |
I am trying to implement a simple quantile regression in R using JAGS:
n <- 200
x <- runif(n=n,min=0,max=10)
y <- 1 + 2*x + rnorm(n,sd=.6*x)
p <- 0.95
jdf <- list(y=y,x=x,p=p)
params <- c("alpha","beta","tau")
mcmcmodel <- jags.model(file="qreg.jag",data=jdf,n.chains=3)
update(mcmcmodel,2000)
mcsamples <- coda.samples(... |
I have just performed some (very) simple linear regression in Genstat and would like to include a succinct and meaningful summary of the output in my report. I'm not sure exactly what or how much of the information I should be including.
The main bits of my Genstat output look like this:
Summary of analysis
Source ... |
We're analyzing a bunch of time domain signals, I want to be able to identify an outlying one.
In our results all the signals will either all be reasonably similar, or in some cases, one should be dramatically different.
Here's an example of a set of four signals including an outlier:
At the moment I'm averaging the... |
I'm trying to compress data using wavelets and I wanted to do it with R. Could anyone tell me if there is such a tool?
Thanks in advance.
|
I am trying to conduct a meta analysis for dose response studies where I am using fractional polynomial transformation from predefined family of powers. Now data fitting using all possible combinations will yield large number of possible models where some of them are clearly not good while there are few models that pro... |
Similar to this question, I want to know if the overlap between two samples is significant. However, my items are not unique; I have $c$ distinct colors of items, there are $m_i$ items of color $i: (1<i<c) $, and $N=\sum m_i$ items total. Does this make a difference?
I have figured out that drawing one sample of n it... |
Update:
I haven't gotten any answers, so I am simplifying my question. Say I measure test scores of $100$ people in one of two conditions. Each test has $10$ items. On each item, each person can receive a score of $0-10$. Each person's test score is the average across items. My question is, is the effect size of the co... |
Following the confusion (on my part) here, and as suggested, I am presenting my question in a neutral way below:
Problem:
I am looking at the relationship between "product research" (variable A) and "product purchase" (variable B). 'Product' means any consumer goods (e.g. toys, clothes etc.).
A and B are composite sco... |
(Thanks a lot for the quick responses! I did a poor job of asking the question, so let me retry.)
I do not know how to find out whether or not the difference between two Spearman's correlations is statistically significant. I would like to know how to find it out.
The reason I wanted to find out is that in the follow... |
I have a representative sample token on area of 60 mq (squared meter) of a territory of 54077 mq. This sample contains the number of little plants that there are for each mq. The sample is defined in R as:
s=c(13,7,10,4,28,0,10,0,0,0,0,0,0,0,0,0,6,
0,0,0,0,0,0,0,4,0,0,0,4,0,0,0,1,2,2,0,
2,3,3,3,1,3,12,33,1,31,... |
In e-commerce site, consumers would provide a overall rating with multi-aspect ratings. For example, if a consumer purchase a camera, he would provide a rating info as follows:
User Product Size/Wight Appearance Battery Price Display Overall
A Camera 1 4 2 3 ... |
Is it enough to show that MSE = 0 as $n\rightarrow\infty$? I also read in my notes something about plim. How do I find plim and use it to show that the estimator is consistent?
|
Consider the training set $\{(x_i; y_i)\}_{i=1}^N, x_i \in \mathbb{R}^n, y_i \in \mathbb{R}$.
The goal is to find regression function, like, $f(x) = \sum_{i=1}^K a_i g_i(x) + a_0$.
The least-squares solution is well known, if we know $g_i$ functions.
Lets consider that we have kernel regression with radial basis functi... |
I have two 2D Gaussian random variables. I'd like to find the weighted average of the two (based on their covariance matrix around the mean, meaning that the mean of the final Gaussian should be closer to the one with the smallest variance). What is the proper way of doing that? Any pointer to web urls around this topi... |
During an experiment for text classification, I found ridge classifier generating results that constantly top the tests among those classifiers that are more commonly mentioned and applied for text mining tasks, such as SVM, NB, kNN, etc. Though, I haven't elaborated on optimizing each classifier on this specific text ... |
Cross posted on StackOverflow.
I have some extremely large sparse matrices created using spMatrix function from the matrix package.
Using the solve() function works for my Ax=b issue, but it takes a very long time. Several days.
I noticed that http://cran.r-project.org/web/packages/RScaLAPACK/RScaLAPACK.pdf appears t... |
I'm working with a sample of test scores which range from 0 to 100. These scores are generated from a set of 100 binary responses (0 or 1), so the higher the resulting sum, the better the performance. The distribution of these scores is definitely not normal: it is highly skewed. I'm interested in carrying out a Box-C... |
I am using the least angle regression (LARS) to extract the most important predictors ($x_1, x_2,...,x_p$) for my response variable ($y$).
I have seven predictors ($x_1,x_2,...,x_7$) for each response variable. I did 10-fold cross validation by using R package lars.
I am making a cut point at 0.62 (approx.). Am I doing... |
Let's say I have some data, i.e. a collection of real numbers.
Are there any good general methods to determine whether this data conforms to a given probability distribution, e.g. the normal distribution, the log-normal distribution, or any other distribution? If so, what are some of the best methods out there?
|
Andrew Gelman, in the book he wrote with Jennifer Hill, states in Chapter 9, (section 9.3), on page 177:
It is only appropriate to control for pre-treatment predictors, or, more generally, predictors that would not be affected by the treatment (such as race or age). This point willl be illustrated more concretely in ... |
I have a collection of datapoints in three dimensions x,y,z.
I'd like to be able to visualize the data as a smooth surface.
Stated another way:
Given those points, I'd like to be able to determine z for any arbitrary x and y such that the surface is smooth and continuous.
Tools available are anything that I can get my ... |
I am trying to write a Monte Carlo simulation in R and I am really stuck! I want to know the probability distribution of a random person in the UK becoming ill from eating a cooked 100g piece of chicken.
I have the following information: out of 1000 pieces of chicken tested 20 had bacteria in question and I have data ... |
For variables A (product research) and B (product purchase), I am proposing to do three levels of analysis as follows:
Test 1: Overall:
The goal here is to see if there is a relationship between A and B. My data is at the interval level and the scatter plot shows a linear relationship, so I am doing bivariate correla... |
I recently started reading Gelman and Hill's, "Data Analysis Using Regression and Multilevel/Hierarchical Models" and the question is based on that:
The sample contains 6 observations on proportions: $p_{1}, p_{2}, \dots, p_{6}$
Each $p_{i}$ has mean $\pi_{i}$ and variance $\frac{\pi_{i}(1-\pi_{i})}{n_i}$, where $n_{i}... |
I collected a data-sets which tested for many users (>100.000) which out of ten features in a software-product they use. They can use multiple features but for each feature there is only "use" or "don't use". So in terms of software-development, I have many sets of features in a length of zero to ten.
I want to visuali... |
Can the percentages in a pie chart add up to more than $100\%$ and the data or analyses will still make sense (or be logical)? Let's say the percentage in a pie chart adds up to $100\%$ . Does this make statistical sense?
|
I am trying to solve a problem for my thesis and I don't see how to do it. I have 4 observations randomly taken from a uniform $(0,1)$ distribution. I want to compute the probability that $3 X_{(1)}\ge X_{(2)}+X_{(3)}$. $X_{(i)}$ is the ith order statistic (I take the order statistic so that my observations are rank... |
This stackoverflow post describes computing a Pearson correlation of [1,2,3] and [1,5,7] in several different ways in Python. The most straightforward implementation from the definition in Wikipedia comes up with
0.973328526785
while Excel, R, NumPy, an online calculator, and a different Python implementation (involvi... |
Let $X_i$ be independent, normally distributed random variables, for $1\leq i\leq N$. What is the distribution of $Y_m=\frac1 N \sum_{i=1}^N X_i^m$?
Every high school student knows part of the answer. The mean of $Y^m$ is the $m$'th moment of the normal distribution, and the variance of $Y^1$ is $1/N$.
I'm interested... |
I wish to estimate the state of a system from two separate and disparate observations. A simple approach that I have seen in some literature is to combine the feature vectors (observations) by simply concatenating them. So if the first observation is denoted $x \in \Re^{10}$ and the second is denoted $y \in \Re^5$, we ... |
I want to calculate correlation coefficient between random vectors and use this for hypothesis testing. The code
bs <- function(qtS, rvNum = 1000)
{
eb <- qtS * rvNum
randVect <- matrix(rnorm(eb), nrow=qtS, ncol = rvNum)
randVect <- randVect/sqrt(sum(randVect * randVect))
randVectCor <- cor(randVect)
randVect... |
I'm going through the book 'Introductory Time Series with R' by Cowpertwait and Metcalfe. On page 36 Its says the lines are at: $-1/n \pm 2/\sqrt{n}$. I've read here R forum that the lines are at $\pm 1.96/\sqrt{n}$.
I ran the following code :
b = c(3,1,4,1)
acf(b)
and I see that the lines look to appear to be ... |
Does cross validation work with an asymmetric loss function?
|
I have two questions related to the concept of "learning consistency" for those who are familiar with statistical learning theory a la Vapnik.
Question 1.
The learning process is called consistent (for the class of functions $\mathcal{F}$ and probability distribution $P$) if
$$
R_{emp}(f^*_l) \buildrel P \over \to \i... |
I was assigned to demonstrate the Central Limit Theorem (CLT) in R in my statistics class. I already made some progress with simulation using simple.sim in R. I want to prepare 3 examples of the CLT with continuous distributions (rnorm, rt and rf) and 3 examples with discrete distributions (rbinom, rpois and rtriangle ... |
I have a bunch of variables which contain longitudinal data from day 0 to day 7. I am looking for an appropriate clustering approach which can cluster these longitudinal variables (not cases) into different groups. I tried to analyze this data set separately by time, but the result was pretty difficult to be reasonably... |
For example, I have historical loss data and I am calculating extreme quantiles (Value-at-Risk or Probable Maximum Loss). The results obtained is for estimating the loss or predicting them? Where can one draw the line? I am confused.
|
For non golfers, each golfer has a handicap based on his scoring history. The handicap predicts, on average, how many shots above par that golfer will take to play 18 holes. In theory, when that golfer plays in a handicap tournament against other golfers with their respective handicaps, he should have the same chance... |
For the lasso problem
$\min_\beta (Y-X\beta)^T(Y-X\beta)$ such that $\|\beta\|_1 \leq t$. I often see the soft-thresholding result
$$ \beta_j^{\text{lasso}}= \mathrm{sgn}(\beta^{\text{LS}}_j)(|\beta_j^{\text{LS}}|-\gamma)^+ $$
for the orthonormal $X$ case. It is claimed that the solution can be "easily shown" to be su... |
We recently studied a model with a likelihood function of the form
$$\Pr(d_i|\omega,t_i)=(1-d_i)+(2d_i-1)\cos^2(\omega t_i),$$
where $d_i\in\{0,1\}$, $\omega$ is an estimation parameter, and $t_i$ are determined by the experimenter. This is a set of independent but non-identically distributed Bernoulli trials (think: ... |
I'm particularly interested in plotting residuals against fitted values, and residuals against predictors. Often times I need to make boxplots of the residuals conditional on predictors.
I'd be interested in functions that include other/multiple diagnostics as well, e.g. ceres plots, qqplots.
The car package has some ... |
I am just wondering what kind of things could cause power to be lost in general (the opposite of reducing the noise of the data to increase the power of the test).
Could anyone give some summary or ideas how to think of the power issue?
|
(Apologies for the ASCII tables, Stackexchange doesn't allow HTML tables and since I'm not supposed to link to an image, this is the only way I know of showing the data)
I'm learning about ANOVA F-testing and stumbled upon this problem:
There exists the following set of data regarding four teaching methods and the scor... |
In the interrupted time series regression, we are interested in the level change or trend change due to a policy change or an intervention event occurance. If the dates of those interventions are known, the model then can be expressed as
y = intercept + coef.time*time(t)+coef.intervention*intervention(t)+coef.time a... |
What quantity can be used to robustly estimate a specific variation of a sequence?
By "specific" I mean "dimensionless, per-unit" etc, that is, independent on units of measurement and independent on mean value.
I started from the normalized deviation, which is the ratio of sequence deviation to sequence range, but thi... |
I'm investigating associations between socioeconomic factors and dichotomous outcome. I use generalised linear models (GLM) with log link for Bernoulli family, i.e., modelling the prevalence ratio.
At the epidemiology course of K.J. Rothman & E.Hatch we were told, that goodness of fit tests are designed to prediction m... |
Just need to check the answer for the following question:
Question
Suppose $X$ and $Y$ are two independent standard normal variables:
$X \sim \mathcal N (0,1)$
$Y \sim \mathcal N (0,1)$
What is the distribution of $X + Y$ ?
My Working
$X+Y \sim \mathcal N ( \mu_1 + \mu_2$, $\sqrt{\sigma_1^2 + \sigma_2^2}) $
$= X+Y \sim... |
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