question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I have a table in which the multiple linear regression results is provided. If I have unstandardized coefficients and standard error for each independent variable, is it possible to calculate standardized coefficient (Beta) and coefficient of determination ($R^2$) from these data. </p>
<p>My friend provided $R^2=0.... | 49,927 |
<p>Let's say I have 7 urns filled with random numbers of colourful marbles. An example dataset is as below:</p>
<pre><code>data <- matrix (c(5,3,4,4,4,2,1,1,1,1,1,2,2,1,2,2,1,1,2,1,4,1,1,2,4,1,3,1,7,1,1,2,1,3,3), ncol = 5);
rownames(data) <- as.character(seq(1,7));
colnames(data) <- c("red", "blue", "yellow",... | 74,183 |
<p>Apologies if this is a very basic question.</p>
<p>If we have data that are not normally distributed (e.g. skewed, Shapiro-Wilk test is significant) and we resort to rank-based methods (e.g. Wilcoxon Signed Rank test), then do we need to be concerned with outliers?</p>
<p>Imagine, for example, we plot the data usi... | 279 |
<p>I'm taking a class on R and I cannot get the professors code to work. I am trying to do a simple linear model and I run this code:</p>
<blockquote>
<p>ozone<-read.table("<a href="http://www.ats.ucla.edu/stat/r/faq/ozone.csv" rel="nofollow">http://www.ats.ucla.edu/stat/r/faq/ozone.csv</a>", sep=",", header=T)</... | 74,184 |
<p>I am seeking a statistic measuring an estimate's reliability or stability as an alternative to the coefficient of variation (CV), also known as the relative standard error. The CV is the standard error of an estimate (proportion, mean, regression coefficient, etc.) divided by the estimate itself, usually expressed a... | 74,185 |
<p>I use <code>escalc()</code> function from <code>metafor</code> package to calculate various effect sizes or outcome measures (and the corresponding sampling variances) that are commonly used in meta-analyses.</p>
<p>In most of articles are tables of <em>mean</em> and <em>standard deviation</em> which can be easily ... | 36,904 |
<p>I want to determine if there's a difference in mean p-values between two groups. In order to do this I perform a Wilcoxon's rank-sum test (the data is not normally distributed). So far, so good. Finally, I want to calculate the corresponding effect size. Unfortunately, R does not provide this. It also does not provi... | 74,186 |
<p>Suppose we have a joint distribution on vector $[\mathbf{x}, y]$:
$$
p([y, \mathbf{x}] ) = \mathcal{N}\left(\begin{pmatrix} y \\ \mathbf{x}\end{pmatrix}| 0, \begin{pmatrix} k& \mathbf{v} \\ \mathbf{v}^T & K\end{pmatrix}\right),
$$
where $\mathbf{x} \in \mathbb{R}^N$, $y \in \mathbb{R}$.
And also we know dist... | 74,187 |
<p>I know that linear regression can be thought as <em>"the line that is vertically closest to all the points"</em>:</p>
<p><img src="http://i.stack.imgur.com/IXibx.png" alt="enter image description here"></p>
<p>But there is another way to see it, by visualizing the column space, as <em>"the projection at the space ... | 74,188 |
<p>I'm trying to build a model that would describe some process of payment and distribution of payments in time. I believe that time of payment has <a href="http://en.wikipedia.org/wiki/L%C3%A9vy_distribution" rel="nofollow">Levy distribution</a> with probability density function:</p>
<p>$ f(x,c)=\sqrt{\frac{c}{2\pi}}... | 38,194 |
<p>I am learning Gaussian kernel SVMs recently. I have to choose the parameter $\epsilon$ for Gaussian kernel,
$$k(x,t)=e^{-\frac{\|x-y\|_2^2}{2\epsilon}}.$$</p>
<p>I try to find the answer in literature. I found some to analyze the parameters like '<a href="http://www.ncbi.nlm.nih.gov/pubmed/20221922" rel="nofollow">... | 74,189 |
<p>I am working on time series analysis. The book I am using ("Statistics for Long Memory Processes" by Jan Beran) uses a number of measures for process memory and one of them is to graph Sample Mean Variance against the sample size (In other words, for every n, the variance of the mean of $X_n$ is graphed).</p>
<p>Th... | 36,907 |
<p>In a normal distribution, the <a href="http://en.wikipedia.org/wiki/68-95-99.7_rule">68-95-99.7 rule</a> imparts standard deviation a lot of meaning. But what would standard deviation mean in a non-normal distribution (multimodal or skewed)? Would all data values still fall within 3 standard deviations? Do we have r... | 20,350 |
<p>I am using panel data and I would like to determine whether I can use the Random Effects (RE) model instead of Fixed Effects (FE) to estimate one coefficient of interest.
When I use the Hausman test comparing FE and RE, I have to reject the null hypothesis (meaning that the RE model is not OK). However, the differe... | 36,910 |
<p><a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI4253.1" rel="nofollow">Perkins et al. (2007)</a> introduce a "skill score" for measuring climate model output against observations. The score basically consists of measuring the overlap between probability density functions of the model (m), and the observatio... | 48,610 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/14500/how-can-a-regression-be-significant-yet-all-predictors-be-non-significant">How can a regression be significant yet all predictors be non-significant?</a> </p>
</blockquote>
<p>X and Y are not correla... | 49,368 |
<p>Apologies for the almost text-book like question. </p>
<p>I have a 2x2 design with fixed categories and a continuous response variable.</p>
<p>If the variances are equal between groups (Bartlett test) and residuals are normally distributed (Shapiro test), ok I can do standard ANOVA. </p>
<p>Otherwise: </p>
<ol>
... | 34,294 |
<p>Intervention analysis in Box-Jenkins framework crosspoinds to time-series regression with arma errors if the noise is stationary or arima errors if the noise is non-stationary. </p>
<p>For a seasonal time series data with increasing trend, the noise model can be express as</p>
<p>$$
N_t = \frac{\Theta(B)}{(1-B)(1... | 74,190 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/35510/why-does-including-latitude-and-longitude-in-a-gam-account-for-spatial-autocorre">Why does including latitude and longitude in a GAM account for spatial autocorrelation?</a> </p>
</blockquote>
<p>I a... | 49,903 |
<p>Based on real data (e.g. spot and futures prices of an index) if two series are correlated in the long run (e.g. strong positive significant correlation) it does not mean that they are cointegrated.</p>
<p>What if two series are cointegrated: can we infer that they are also correlated in the long run? Can we find a... | 74,191 |
<p>I am trying to simulate a process of selection without replacement. The process is one in which the system places a set of items in a specific order, and then the user selects N items in whatever order they want. The order of the items will vary depending on an algorithm. </p>
<p>The probability that each item will... | 74,192 |
<p>I understand how best split is chosen for random forest for numerical predictors (features). </p>
<p>Numerical predictors are sorted then for every value Gini impurity or entropy is calculated and a threshold is chosen which gives the best split. But how best split is chosen for categorical predictor as there is no... | 49,622 |
<p>I am trying to fit a linear model (<code>lme4::lmer()</code>) to my data in R. I would like to look at a number of things, including "<strong>scrambling</strong>" of visual stimuli and "<strong>intensity</strong>" of the emotions portrayed therein. These things are stored the "<strong>scrambling</strong>" and "<stro... | 74,193 |
<p>I am frequentist by training and practice, but I'd like to learn more about Bayesian statistics. I know the basics, but I would be at a loss if I had to, for example, replace my normal ANOVA hypothesis testing approach with a Bayesian alternative.</p>
<p>What book would you recommend to learn practical Bayesian app... | 36,918 |
<p>I have a dataset (data1.csv) that contains some missing data ** . ** (missing at random), I am creating a subset from this dataset (d1) such that only complete observations are retained in d2. I am using the <strong>ftable</strong> , <strong>as.data.frame</strong> function and creating a column <strong>p</strong> t... | 74,194 |
<p>Consider 10 values that follow a standard normal distribution. What would you expect to be the lowest value?</p>
<p>I tried to simulate this problem in R. I basically just simulated 100000 standard normal distribution with 10 values and took the mean of the each lowest value.</p>
<pre><code>> mean(replicate(100... | 36,920 |
<p>Training data with $p$ =11 predictors and $n$ =165 with 4-class problem was cross-validated (5 times repeated 10-fold CV) using the sparse LDA (aka SDA) using <code>caret</code> package. This model is a regularized version of LDA with two tuning parameters: <em>lasso</em> using $\ell_{1}$ penalty and ridge using the... | 74,195 |
<p>I'm reading the GPML book and in <a href="http://www.gaussianprocess.org/gpml/chapters/RW2.pdf" rel="nofollow">Chapter 2 (page 15)</a>, it tells how to do regression using Gaussian Process(GP), but I'm having a hard time figuring how it works.</p>
<p>In Bayesian inference for parametric models, we first choose a pr... | 36,921 |
<p>I'm trying to differentiate two groups of patients using various machine learning algorithms, including support-vector machines (SVM). </p>
<p>As far as the details of the analysis go, I would like to train the sample on a separate group and cross-validate on another. </p>
<p>The problem is that patients are diffe... | 36,922 |
<p>I have a collection of training documents with publication dates, where each document is labeled as belonging (or not) to some topic T. I want to train a model that will predict for a new document (with publication date) whether or not it belongs to T, where the publication date might be in the past or in the future... | 15,738 |
<p><strong>Question</strong></p>
<p>In some bank, the time it takes from the moment a customer arrives until a clerk is available is distributed normally with $\mu=15,\sigma=2$</p>
<p>a. What's the probability for the next client to wait more than 18 minutes?</p>
<p>b. What's the prob. that the average waiting time ... | 74,196 |
<p>I am looking for a working algorithm for find out optimal kernel bandwidth for density estimation. I need to write my own program in pascal instead of using R or Matlab. So far all algorithms I found failed. For example, this one looks simple and promising:</p>
<p><a href="http://www.di.ubi.pt/~lfbaa/entnetsPub... | 19,101 |
<p>I found that the probability of an event occurring is an algebraic function of all the probabilities that I want to find;</p>
<p>$$P(v_1,v_2,v_3,...,v_n)=p_{collected}$$</p>
<p>For small $n$, it would be easy to solve for all $v$ as a system of equations. However, as $n$ grows large (in the order of hundreds to s... | 36,927 |
<p>I have been having a hard time deciding which statistical test to choose for a dataset. The more a read on the web, the more I get confused since frequently there are different opinions when it comes to chose the right test.</p>
<p>To this extent, when in doubt, I apply one parametric and one non-parametric tests, ... | 74,197 |
<p>After doing k-means clustering on a set of observations, I would like to construct a discriminant function so as to classify new observations into the categories I found after k-means. Is this at all a good idea? What should I be careful with?</p> | 36,928 |
<p>These two functions exist in R but I don't know their differences. It seems that they only return the same p-values when calling <code>wilcox.test</code> with <code>correct=FALSE</code>, and <code>wilcox_test</code> (in the coin package) with <code>distribution="aymptotic"</code>. For other values they return differ... | 37,492 |
<p>Suppose I am doing some experimental procedure on two treatment groups. The procedure has several stages, each of which may fail. Failure at any stage halts the experiment. If all stages are passed then there is some useful result.</p>
<p>Although I'm primarily interested in the final result, the treatments <strong... | 74,198 |
<p>I have a dataset that has both continuous and categorical data. I am analyzing by using PCA and am wondering if it is fine to include the categorical variables as a part of the analysis. My understanding is that PCA can only be applied to continuous variables. Is that correct? If it cannot be used for categorical da... | 48,631 |
<p>There are 8 people playing poker.</p>
<p>So, the odds of winning the entire round = 1/8</p>
<p>2 rounds are played, and Bill wins both rounds.</p>
<p>What are the odds this was random? (Hypothesis test?)</p>
<p>NullH = Bill has no added skill. (Got lucky)</p>
<p>AltH = Bill has skill.</p>
<p>p = .13 = 1/8</... | 36,934 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/6/the-two-cultures-statistics-vs-machine-learning">The Two Cultures: statistics vs. machine learning?</a> </p>
</blockquote>
<p>What is the difference between data mining and statistical analysis?</p>
<p>... | 48,439 |
<p>I have a ranking of books that is based on number of sales and I want to improve it to include how many countries the book was sold in and number of libraries that carries it</p>
<pre><code>Book rating 1 = # sales
Book rating 2 = # sales + # countries + # libraries
</code></pre>
<p>Can I say that Book rating 2 i... | 74,199 |
<p>Let $f\left(x\right)$ be the probability density function of the
random variable $X$. What is the joint probability distribution of
$f_{X,Y}\left(x,y\right)$ if $Y=X$? </p>
<p>Thanks for any helpful answer.</p> | 74,200 |
<p>I have data for multiple people, where each person performs and is graded on a task an arbitrary number of times each year across multiple years. E.g. - </p>
<pre><code> year 1 year 2 year 3
Person1 1 1 3 2 4 2 3 3 5 2 3 4 1
Person2 2 3 1 7 9 1 2 3 3... | 36,938 |
<p>Having looked at multiple online sources, I can't seem to get a straight answer. Could someone please clarify for me if ordinal data is sufficient to use for the WSRT and if not, is the sign test an appropriate alternative?
Finally, this is for my dissertation project at university and so if any references/literatur... | 36,939 |
<p>Let's say the following is data for airplane accident death to total.</p>
<pre><code>Country Sky Total death Total individual traveler
A 30 10,000
B 60 15,000
C 3000 10,000,000
</code></pre... | 74,201 |
<p>Can somebody provide an intuitive difference between correlation and correlation coefficient? During learning of weights of neural network, I want to show how closely the estimated weights are to the known true weights. For this, I was thinking of using the correlation measure. If they are correlated then the value ... | 74,202 |
<p>I need to be <em>neat</em> in measuring the success rate of a treatment. It is anyway pretty high. But as it is all about ecology, multpliying experiments is difficult.</p>
<p>I have treated $N = 20$ individuals, $18$ succeded. This is a $\tau = .9$ success rate.</p>
<p>I used the <em>Jeffrey's table</em> to get t... | 74,203 |
<p>I have fitted a Poisson regression to my claim frequency.</p>
<p>I have obtained the following result:</p>
<pre><code> Estimate Std. Error z value Pr(>|z|)
(Intercept) -19.95861 1139.33678 -0.018 0.9860
make -0.10534 0.04116 -2.559 0.0105 *
agevehO 0.05983... | 74,204 |
<p>I have two normal distributions, and I want to test whether they have the same standard deviation, I really don't care about the mean.</p>
<p>My idea is: de-mean both of them and then use <a href="http://en.wikipedia.org/wiki/Kolmogorov%E2%80%93Smirnov_test" rel="nofollow">Kolmogorov-Smirnov</a> to test if the dist... | 74,205 |
<p>The general disjunction rule for events $A_1$ and $A_2$ is $$P(A_1 \vee A_2) = P(A_1) + P(A_2) - P(A_1 \wedge A_2).$$
What about when there are $n$ events? What is $P(\bigvee_i^n A_i)$ where $A_i$ is the $i$th event?</p> | 74,206 |
<p><img src="http://i.stack.imgur.com/agsGZ.png" alt="enter image description here">
<img src="http://i.stack.imgur.com/fgfjT.png" alt="enter image description here"></p>
<p>I took the residual of a historical stock price $\hat e_t=r_t-\hat \mu_t$, where $r_t$ is the return of a stock and ran ACF and PACF. From the AC... | 74,207 |
<p>I am interested in stochastically modeling whether the market is likely to go on in the same direction(trend), or reverse and head back. This is all for intraday purposes, next 1-2 ticks kind of strategy with 30sec - 3 mins holding times.
How can I attack this problem? Where do I start? </p> | 74,208 |
<p>I am reading some books about hypothesis testing, but I am not sure if my following reasoning makes sense:</p>
<p>Assume I have a gaussian random variable $X \sim N(\mu, \sigma)$ with $\sigma=1$.
Now I obtain 5 iid samples, $x_1, \cdots, x_5$.</p>
<p>I want to check if $\mu<0$. So I set up the null hypothesis a... | 74,209 |
<p>Or more so "will it be"? <a href="http://en.wikipedia.org/wiki/Big_data">Big Data</a> makes statistics and relevant knowledge all the more important but seems to underplay Sampling Theory. </p>
<p>I've seen this hype around 'Big Data' and can't help wonder that "why" would I want to analyze <strong>everything</stro... | 74,210 |
<p>If I have two different percentages and I wanted to know the change, I would simply use the percentage change formula...but what if I want to compare two percentages that have different amounts:
Ex: August - there was 539 right answers out of 743 = 72.5 %
September - there was 498 answers out of 820 = 60.7%</p>
<p... | 74,211 |
<p>I am trying to mine product-usage sequences for multiple users of online gaming site. I have found the R package <a href="http://cran.r-project.org/web/packages/arulesSequences/index.html" rel="nofollow">arulesSequences</a> but am not sure how to fit it to my problem. The data format would be tuples similar to those... | 74,212 |
<p>Has the idea of a <a href="http://en.wikipedia.org/wiki/Maximum_entropy_probability_distribution" rel="nofollow">maximum entropy probability distribution</a> been explored for function spaces, and if so what are some key papers, books, or terms to look for?</p>
<p>For $\mathbb{R}^n$ (and discrete spaces), the probl... | 74,213 |
<p>Let $p$ be some probability distribution with a density $f$.</p>
<p>$p$ is defined over $\Omega$.</p>
<p>Is it true that for any $\omega \in \Omega$, $p(\omega) = 0$?</p>
<p>If not, what are the "minimal conditions" under which $p(\omega) = 0$ for any $\omega$ (the space $\Omega$ is actually a subset of $\mathbb{... | 36,953 |
<p>I am currently completing my dissertation. My study is cross-cultural and looks at predictors and inhibitors to adoption of technology in two countries (Thailand and Australia). I have a hypothesised model with IV's (Ease of Use, Usefulness, Need for Interaction, Risk, and Social Influence) directly linked to a sing... | 74,214 |
<p>I've come accross a term called "statistical efficiency of the median" in a paper and couldn't find any definition in the paper. From my search online, I found that this might mean relative efficiency of the median compared to the mean.</p>
<p>Can anyone shed some light to where I can look for clues?</p> | 13 |
<p>We're working with some logistic regressions and we have realized that the average estimated probability always equals the proportion of ones in the sample; that is, the average of fitted values equals the average of the sample.</p>
<p>Can anybody explain me the reason or give me a reference where I can find this d... | 49,757 |
<p>Again this question may be simple for you, but it is an important aspect for my classification problem. Let`s say I have 5 attributes, which are:</p>
<pre><code>- previous_value_1
- previous_value_2
- previous_value_3
- previous_value_4
- previous_value_5
</code></pre>
<p>These attributes are generated with indepe... | 74,215 |
<p>Following my earlier question <a href="http://stats.stackexchange.com/questions/16524/multidimensional-vs-unidimensional-measure">here</a>, is there a quick way (using Excel or SPSS) to ascertain/calculate the reliability of composite scores. </p>
<p>Reliability in this case is for me to say confidently (i.e. the o... | 48,665 |
<p>I am currently generating data by simulating a model of chemical system under different conditions (temperature) over time. In each simulation, the starting structure being modeled is exactly the same - only the temperature is different. The system is allowed to propagate over time and the length and number of obser... | 74,216 |
<p>I used my training dataset to fit cluster using kmenas function</p>
<pre><code>fit <- kmeans(ca.data, 2);
</code></pre>
<p>How can I use fit object to predict cluster membership in a new dataset?</p>
<p>Thanks</p> | 74,217 |
<p>I have 30 variables and am trying to select the best model. I have run the following methods on a 'large' data set (having removed a smaller test set): </p>
<ul>
<li>OLS, </li>
<li>best subset selection, </li>
<li>stepwise selection, </li>
<li>ridge regression, </li>
<li>LASSO, </li>
<li>PCR and </li>
<li>PLS. </li... | 34,587 |
<p>I'm a first year statistics graduate student taking a course in regression. In the previous chapter we covered, we discussed partial F-tests for deciding whether to include a predictor variable. In the current chapter (which we just finished), we covered six model selection criteria. I was expecting these two con... | 74,218 |
<p>This may be a silly question, but I'm not seeing a clear answer in any of the usual sources. I'm preparing to build a Bayesian model to fit with BUGS/JAGS, currently working through the model logic in plate notation.</p>
<p>I have a few kinds of observed variables, and several latent variables. I know that a Baye... | 36,960 |
<p>Is a p-value from a traditional significance test the same as the false alarm value in the Bayesian rule? And/or is it "close enough" to give correct results when used that way?</p>
<p>The definitions of the two terms seem to be talking about the same things, but I know it's easy to be tripped up by subtleties. W... | 74,219 |
<p>Assume that I have a variable whose distribution is skewed positively to a very high degree, such that taking the log will not be sufficient in order to bring it within the range of skewness for a normal distribution. What are my options at this point? What can I do to transform the variable to a normal distribution... | 74,220 |
<p>I observe draws of some random variable $Y$ over time where $Y_{t} = aY_{t-1} + \epsilon_{t}$.</p>
<p>$\epsilon \sim N(0, 1/\rho_\epsilon)$ and $a$ is an unknown parameter with prior distribution $a \sim N(\mu_0, \Sigma_0)$.</p>
<p>Since both the noise and the prior are normal, after we observe $Y_t$, the posterio... | 74,221 |
<p>I have a problem that I don't think I've met before.
I have N observations of the variables v1 and v2 and I assume that there is a function f such as v2 = f(v1).</p>
<p>I want to know if f has a particular 'statistical' monotony (increasing or decreasing) and if it is 'statistically' convex or concave.
By 'statisti... | 36,962 |
<p>Let $(X,Y)$ have the mixed discrete-continuous pdf given by:</p>
<p>$$f(x,y)= \begin{cases} \frac{y^{a+x-1}e^{-2y}}{\Gamma(a) x!}\ y>0;x=0,1,2,\ldots \\ 0 \ \ \ \ \ \ \ \ \ \ \ \ \ \ \text{elsewhere} \end{cases}$$</p>
<p>Could you please help me show that this nasty pdf integrates/sums to 1 over the support of... | 74,222 |
<p>I used the following R code to fit a probit model:</p>
<pre><code>p1 <- glm(natijeh ~ ., family=binomial(probit), data=data1)
stepwise(p1, direction='backward/forward', criterion='BIC')
</code></pre>
<p>I want to know what does <code>stepwise</code> and <code>backward/forward</code> do exactly and how select th... | 74,223 |
<p>This is a homework questions. Can you guys give me some hints?</p>
<p>Let $U_{(1)}<\cdots<U_{(n)}$ be the order statistics of a sample of size $n$ from a Uniform$(0,1)$ population. Show that $F^{-1}(U_{(1)})<\cdots<F^{-1}(U_{(n)})$ are distributed as the order statistics of a sample of size $n$ from a p... | 74,224 |
<p>I have difficulty understanding how self organizing maps (SOM) are doing dimensionality reduction. Can anybody provide a useful explanation to me?</p>
<p>Suppose we have 20 training data points in 50 dimensions. Let's say, I have specified 3 by 3 SOM (lattice with 9 points), I embed my manifold (3 by 3 lattice) to ... | 36,966 |
<p>Been reading through C.R.Rao's (1975) Simultaneous Estimation of Parameters in Different Linear Models and Applications to Biometric Problems, Biometrics, Vol. 31, No. 2 (Jun., 1975), pp. 545-554.</p>
<p>On P550 he notes "that if V (the correlation matrix for the current observations) is unknown then it cannot be c... | 36,967 |
<p>I have a dataset containing $p$ variables (or columns) denoted by $X_i$ for $i=1,...,p$. I am trying to cluster this dataset using <a href="http://en.wikipedia.org/wiki/Self-organizing_map" rel="nofollow">Self-Organizing Map</a>. There are 3 main variables within these $p$ variables say $X_1$, $X_2$ and $X_3$. The r... | 36,968 |
<p>I would like to ask the difference between the normal distribution and the multinomial distribution because I don't know when to use each of them.
I know the normal distribution is used for continuous probability, and the multinomial distribution is used for probabilities of <em>K</em> kinds of categories.</p>
<p>C... | 36,969 |
<p>At first I thought the order didn’t matter, but then I read about the gram-schmidt orthogonalization process for calculating multiple regression coefficients, and now I’m having second thoughts.</p>
<p>According to the gram-schmidt process, the later an explanatory variable is indexed among the other variables, the... | 74,225 |
<p>Both bootstrap and jackknife methods can be used to estimate bias and standard error of an estimate and mechanisms of both resampling methods are not huge different: sampling with replacement vs. leave out one observation at a time. However, jackknife is not as popular as bootstrap in research and practice. My quest... | 74,226 |
<p>I have 2 daily time-series, each 6 years long. While noisy, they are both clearly periodic (with a frequency of ~1 year), but appear to be out of phase. I would like to estimate the phase difference between these time-series.</p>
<p>I've considered fitting curves of the form $a\sin(\frac{2\pi}{365}t - b)$ to each t... | 36,970 |
<p>Disclaimer: I know absolutely nothing about statistics. I've had trouble searching for answers to my question, as I don't have much knowledge about the terminology of statistics.</p>
<p>I'm currently trying to plot a graph with two sets of values that are widely different. This doesn't really matter, but I'm doing... | 37,452 |
<p>Plotting a <strong>glm</strong> binomial model is reasonably simple with the <strong>predict</strong> function. I'm having trouble creating a similar plot for a <strong>glmer</strong> model; predict doesn't work: </p>
<pre><code>id <- factor(rep(1:20, 3))
age <- rep(sample(20:50, 20, replace=T), 3)
age ... | 36,972 |
<p>I'm a part of a volunteer organization that organizes a bunch of events. For each event, members need to submit an application in order to attend the event. A lot of people want to go to these events and we only have a limited number of spots available, so the selection process is usually pretty competitive. The ... | 36,974 |
<p>Generating n random variables whose summation will be 1. [<em>I got the answer.</em>]</p>
<p><strong>EDIT</strong></p>
<p>On genetic algorithm, we have to maintain population. Say, I have two individuals <strong>a</strong> and <strong>b</strong>. Every individual consists of $n$ pairs of ($x_i, \theta_i$), where $... | 74,227 |
<p>I have bivariate data from which I have generated thousands of bootstrapped estimates within each of two conditions (pink & blue):</p>
<p><img src="http://i.stack.imgur.com/EnBqf.png" alt="bivariate data"></p>
<p>I'd like to determine whether these conditions' bivariate distributions have different central ten... | 36,978 |
<p>If one wanted to use Kernel Regression in a Bayesian Framework, any ideas on how one would go about it? </p>
<p><a href="http://en.wikipedia.org/wiki/Kernel_regression" rel="nofollow">Kernel Regression</a></p> | 74,228 |
<p>I'v been playing around with back propagation, trying to see if I can find a solution to the XOR problem using a 2-2-1 network. Based on my simulations and calculations, a solution is not possible without implementing a bias for every neuron. Is this correct?</p> | 74,229 |
<p>I'm using rb-libsvm and the RBF kernel to make classifications. <code>svm.predict(measurements)</code> returns either -1.0 or 1.0. Is there a way to get a confidence for this classification? I am interested in throwing out low-confidence classifications and tweaking precision/recall.</p> | 74,230 |
<p>(Ross [2009], p.162) The current in a semiconductor
diode is often measured by the Shockley equation
I = I0(e^aV-1)
where V is the voltage across the diode; I0 is the reverse current;
a is a constant; and I is the resulting diode current. Find E(I ) if a = 5, I0= 10^-6
, and V is uniformly distributed over [1; 3].
A... | 74,231 |
<p>I was reading this <a href="http://arxiv.org/pdf/1206.4762.pdf" rel="nofollow">article</a>, where the author says that
Maximum Likelihood (ML) estimates are asymptotically normal if
the log-likelihood is asymptotically quadratic.</p>
<p>I have heard or read other times about the likelihood being asymptotically
qu... | 36,980 |
<p><strong>Question:</strong>
I want to test a medicine and I have two groups of people with baseline blood pressure, one I give medicine A and the other one medicine B. After 6 months, I measure their blood pressure.</p>
<p>Now there are two options:</p>
<ul>
<li>I measure the difference of the mean change. </li>
<l... | 36,981 |
<p>$\newcommand{\Var}{\mathrm{Var}}$
Consider $Z_i$ as a binary random variable with $\mathrm{Pr}[Z_i = 1] = \pi$. Also, consider $Y_i$ as:</p>
<p>$Y_i|Z_i = 0 \sim \mathrm{Poisson} (\lambda_0) $</p>
<p>$Y_i|Z_i = 1 \sim \mathrm{Poisson} (\lambda_1) $</p>
<p>My question is how we can find $\Var(Y_i)$.</p>
<p>Here i... | 74,232 |
<p>In Rapid Miner, I created a predictive model (SVM) with Kernel type = polynomial, c= 10, and obtained 80.77% accuracy using cross validation. When compared to hold out set my accuracy on the test set was: 71.54472%. That is 9.23% difference. My questions are
1) Is my SVM model overfit?
2) I created other models ... | 36,986 |
<p>Using wikipedia I found a way to calculate the probability mass function resulting from the sum of two Poisson random variables. However, I think that the approach I have is wrong.</p>
<p>Let $X_1, X_2$ be two independent Poisson random variables with mean $\lambda_1, \lambda_2$, and $S_2 = a_1 X_1+a_2 X_2$, where... | 74,233 |
<p>I want to fit a Cox PH model with random effect (Gamma frailty). Here is an example with 'kidney catheter' data set:</p>
<pre><code> > library(survival)
> data(kidney)
> fit <- coxph(Surv(time, status)~ age + sex + disease + frailty(id), kidney)
> fit
Call:
coxph(fo... | 74,234 |
<p>I ran some experiments first. Afterwards, I looked for the parameter $p_{max}$ for which I can claim the chance a matrix has the ESP-property is $p_{max}$ or lower to a significance of exactly 99%. Is this correct on a more philosophical basis?</p>
<p>I'm doing research in computer science, and have a test to deter... | 74,235 |
<p>I wrote a script to do some analysis and it was working fine until I tried to impliment a while loop to find the number clusters appropriate for k-means. For some reason it keeps saying that an argument is of length zero, but there shouldn't be any. I'm running this remotely, and it works fine locally.</p>
<pre><co... | 36,989 |
<p>Let's say I have a set of scalar values $V$ that I sampled from a set $S$. I want to test whether a given value $X$ could be a member of $S$ or not.</p>
<p>I understand that if the values in $V$ are distributed normally, then we can find the mean and standard deviation, after which you can determine the probabilit... | 74,236 |
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