question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>Good day! </p>
<p>I'm a second year psych grad student. From my fascination with formal logic, I wondered (just personal; not homework) about how to statistically establish necessary/sufficient relationships between variables. </p>
<p>Let's suppose two variables, Intelligence and Creativity, whose relationship is ... | 73,434 |
<p>I have a matrix with about 550k elements (2500 x 220) with 100k values known and the rest are unknown.</p>
<p>Would it make sense to use matrix completion in this case, or are there too many values which are missing? What should I be careful of when I use matrix completion with it, if there are enough values there?... | 73,435 |
<p>I would like to test two relatively small samples against the null hypothesis that both their means and variances are the same. The alternative would be that they in fact differ. I saw a post on this site advocating a ML test but I recall there is also a named test for this case, which I would ideally like to use in... | 38,105 |
<p>Mathematically an AR model is expressed as:
$$ X_t = -\sum_{i=1}^p a_i X_{t-i} + \eta_t$$</p>
<p>Resources say that $\eta_t$ is a white gaussian noise. Is this $\eta_t$ the residual error? When invoking Matlab commands like <code>ar()</code> or <code>arburg()</code> or <code>aryule()</code> do we take into account ... | 73,436 |
<p>Suppose that I have an assortment of summary statistics on a sample, and some beliefs about the underlying distribution, but no access to the sample itself. Each of the sets of summary statistics is sufficient to allow me to estimate the parameters of the distribution that I believe applies. For, instance, I may ha... | 73,437 |
<p>The cost function of my TreeBagger class and fitensemble (Bag method) are both [0 8;1 0] for binary classification. The confusion matrix on fitensemble shows that the classfication tends to turn in the favor of the costy class (like [100 0; 20 80] favoring false negatives) but the same on TreeBagger does not hold. I... | 37,790 |
<p>I was wondering what's the difference between variance and standard deviation? </p>
<p>If you calculate it its is clear that you get the standard deviation out of the variance...</p>
<p>But what does that mean in terms of the distribution you are looking at?</p>
<p>Why do you really need a standard deviation?</p>... | 49,832 |
<p>Patients arrive randomly and independently at a doctor's surgery from
8·0 A.M. at an average rate of one in Five minutes.The waiting room holds 2
persons. What is the probability that the room will be full when the doctor
arrives at 9·0 A.M.?</p>
<p>Answer is 53.84%</p>
<p>I have tried Poisson distribution with pa... | 25,010 |
<p><b>Summary:</b> The last formula boxed in red (which is a modified log likelihood from logistic regression) is a special non-differentiable loss function that is adapted to contain a Bonferroni correction in the loss function. The function is non-differentiable with respect to theta which is a problem for gradient d... | 73,438 |
<p>I have collected temperature readings for 4 locations on a beach in Cornwall UK using data loggers. The loggers recorded temperature every 15 mins accurate to .1 of a degree (Celsius). The loggers collected data for 10 days with a one day break to calibrate the sensors. In total I used 30 sensors with 6-7 sensors in... | 49,621 |
<p>We are extracting features from EEG, which is a time dependent signal.</p>
<p>We have signals of 10,000 datapoints over 64 channels, and we extract 10 features per timestamp per channel, so at the end we have a feature data set of 64x10 features for each time step.</p>
<p>We are applying PLS to regress against han... | 73,439 |
<p>I have 5 different computational tasks. I executed both tasks on two laptops named LA and LB. Out of 5 tasks, 4 tasks were computed in less time on LB, while 1 task took less time on LA. I want to measure, that the achieved performance gain is significant or not. Below is my data example:</p>
<pre><code> ... | 27,661 |
<p>I'm trying to find out the name of a distribution that is like negative binomial, only for finite population and without replacement. Or like Hypergeometric distribution where the last event has to be a success.</p>
<p>That is:</p>
<p>Let's say we have N balls in an urn, where W of them are white balls and B are ... | 48,371 |
<p>Can some of you tell me why the following holds true?:</p>
<p>$ P(A \& B^C )= P(A)-P(A\&B)$ in which: $ B^C$ is $B$ complement.
In which: $A$ and $B$ are independent.</p>
<p>thanks..</p> | 35,823 |
<p>I'm working on a data set for order prediction/classification and a close deadline upcoming. Fortunately, my university has a super-computer with restricted access. I was thinking of using a few nodes (each node is a 16-core processor, 2.3 GHz each and 32 GB of memory running on linux) to overcome the time limitatio... | 35,824 |
<p>To my understanding, "Control" can have two meanings in statistics.</p>
<ol>
<li><p>Control group: In an experiment, no treatment is given to the member of the control group.
Ex: Placebo vs Drug: You give drugs to one group and not to the other (control), which is also referred as "controlled experiment". </p></l... | 73,440 |
<p><img src="http://i.stack.imgur.com/9JFmv.gif" alt="enter image description here"></p>
<p>In the chart above, how can I derive the area between the two graphs, taking into consideration positive and negative areas?</p>
<p><img src="http://i.stack.imgur.com/lP3EJ.gif" alt="enter image description here"></p> | 73,441 |
<p>Assuming that the distribution has finite variance (a condition not required for the LLN), then doesn't the LLN follow from the CLT?</p> | 35,827 |
<p>Let's say I am building a logistic regression model where the dependent variable is binary and can take the values $0$ or $1$. Let the independent variables be $x_1, x_2, ..., x_m$ - there are $m$ independent variables. Let's say for the $k$th independent variable, the bivariate analysis shows a U-shaped trend - i.e... | 73,442 |
<p>Beta stability in linear regression with high multi-collinearity?</p>
<p>Let's say in a linear regression, the variables $x_1$ and $x_2$ has high multi-collinearity (correlation is around 0.9).</p>
<p>We are concerned about the $\beta$ coefficient stability so we have to treat the multi-collinearity.</p>
<p>The t... | 73,443 |
<p>I came across a topic I am somewhat confused about: the merging of two variables.</p>
<p>Assume we have two measurements from the same subjects. The two variables ($x_1$ and $x_2$) are measuring something similar, but not exactly the same thing. The variables (or combined variable, called $x_{12}$) will later be ... | 47,228 |
<p>We're creating a chart showing traffic by time of day over a given period. So the y-axis is traffic, the x-axis is midnight, 1am, 2am, etc. It could also be days of the week. What's the generic name for this type of chart? I've come up with "cycle chart". Is that the standard? Is there one?
<img src="http://i.stack.... | 73,444 |
<p>I am required to analyse samples a compositional data set. However my samples come from seven different locations. Is there any way for me to check if there is a location/mean effect in the data which I can remove from the Isometric Log Ratio (ILR) transformation of the data before analysing? Can I carry out the tes... | 73,445 |
<p>I would like to test how well my model fits the data. The response is binary and the Chi-Squared Test cannot be applied for the residual deviance because the $n_i$ are $1$. To use the Chi-Squared GOF Test, the $n_i$ need to be $\geq 5$. What's an alternative method can I use to test for goodness of fit?</p> | 73,446 |
<p>We know that density for a student-t distribution is given as</p>
<p>$$\frac{\Gamma(\frac{\nu + 1}{2})}{\Gamma(\frac{\nu}{2})} \left(\frac{\lambda}{\pi\nu}\right)^{\frac{1}{2}} \left[1+\frac{\lambda(x-\mu)^2}{\nu}\right]^{-\frac{\nu+1}{2}}$$</p>
<p>with
$\text{E}(X) = \mu$,
$\text{var}(X) = \frac{1}{\lambda}\fra... | 35,831 |
<p>I like to find the feature weights in a <a href="http://en.wikipedia.org/wiki/Structured_support_vector_machine" rel="nofollow">structured SVM</a> for ranking the features w.r.t. importance. I know that in a binary SVM the weight vector can be written as a <a href="http://pyml.sourceforge.net/doc/howto.pdf" rel="nof... | 73,447 |
<p>Let's say I'm performing regularized regression and I want to validate the results using holdout. (I'm choosing holdout instead of cross-validation because my dataset is fairly large, so computational power is an issue and the difference between holdout and cross-validation estimates will likely be negligible.) I ... | 73,448 |
<p>Why the expected value $\int h(x)f(x)$ is desired for inference in Dirichlet Process Mixture?
What is the intuition for MCMC in Dirichlet Process Mixture?</p>
<p>$f(x)$ is the probability density function, and $h(x)$ is the outcome of the Dirichlet Process Mixture (I am not sure).</p>
<p>This formula is originally... | 73,449 |
<p>I have a 2D plane (a large rectangle) with a finite size in the x and y direction, which is the field of my problem.</p>
<p>The field is covered by $n$ smaller rectangles that are located randomly within its bounds (the smaller rectangles are free to overlap each other).</p>
<p>If I "sample" the field at some rand... | 73,450 |
<p>I'm trying to generate random integers which have Poisson distribution. <a href="https://www.gnu.org/software/gsl/manual/html_node/The-Poisson-Distribution.html#The-Poisson-Distribution" rel="nofollow">The open source library GSL has one such distribution</a>.</p>
<blockquote>
<p>Function: <code>unsigned int gsl_... | 73,451 |
<p>Do you know <a href="http://en.wikipedia.org/wiki/Bradley_Efron" rel="nofollow">Bradley Efron</a>? He's a great man.<br>
How did Efron imagine or think about "bootstrap" for the first time?</p> | 73,452 |
<p>I'm a fairly inexperienced statistician fighting a huge deadline and just need some peace of mind that I'm not making a massive error here. I'd be most grateful for any pointers.</p>
<p>I've been working on fitting an <code>lmer()</code> model that explores the spatial relationships between crime and socio-economic... | 73,453 |
<p>I have an interesting modelling problem in which I am trying to forecast the occurrence of a type of weather event using an empirical model driven by measurements of a number of different physical quantities in different locations.</p>
<p>There are a number of complications. First, the predictor measurements are no... | 73,454 |
<p>I have monthly usage data (spanning 3 years) for a customer base of around 200K, and I need to generate 1-month ahead forecasts for each of them. There are a couple of exogenous variables that would need to be included too.</p>
<p>One way to go about is to build an "Arima with exogenous variables" model for each cu... | 73,455 |
<p>I am trying to test whether means of two populations with lots of zeros are different. Here is the following python code example:</p>
<pre><code>from scipy.stats import mannwhitneyu
import numpy as np
a = np.random.random(100)
b = np.random.random(100) * 2
aa = np.hstack((a, np.zeros(1000)))
bb = np.hstack((b, n... | 12,805 |
<p>I recently read a paper in which the authors used Cronbach's $\alpha$ and $\omega$ as measures for unidimensionality and homogeneity. In case of $\alpha$ I know that it is wrong, but I am not so familiar with $\omega$. The literatur I read said it is the proportion of test variance due to a general factor. Does that... | 35,841 |
<p><strong>Question:</strong>
Consider $n$ random variables $x_1, x_2,\cdots x_n\sim \mathcal{N}(0,1)$. The expected value of the $i$th order statistic (the maximum) can be written as</p>
<p>$E(\mathcal{O}^n_1)= \displaystyle\int_{-\infty}^{+\infty}nx\Phi(x)^{n-1}\phi(x)\:dx$.</p>
<p>I wish to show that for $n_1<n... | 73,456 |
<p>I have relatively large (100k items) dataset which I need to split in two groups. So far I've tried knn and the results are not good mainly because I have disproportion in my training data: 90% of points belong to the first group. The same proportion is expected to be in test data.</p>
<p>Is there a way to improve ... | 73,457 |
<p>Wikipedia <a href="http://en.wikipedia.org/wiki/Sample_%28statistics%29" rel="nofollow">defines a sample</a> as:</p>
<blockquote>
<p>a subset of a population.</p>
</blockquote>
<p>While exploring the reason why we divide by $(n-1)$ instead of $n$ when calculating standard deviation (discussed in <a href="http://... | 73,458 |
<p>I'm reading "The Drunkard's Walk" now and cannot understand one story from it.</p>
<p>Here it goes:</p>
<p><i>Imagine that George Lucas makes a new Star Wars film and in one test market decides to perform a crazy experiment. He releases the identical film under two titles: "Star Wars: Episode A" and "Star Wars: Ep... | 73,459 |
<p>I have a data set with ~ <code>7 million</code> rows, of which ~ <code>100k</code> are positives. I'm looking to shrink the data by keeping all the positives and then randomly sampling <code>several hundred thousand</code> negative examples to round out the data set.</p>
<p>I'm uncertain what the guidelines are th... | 35,844 |
<p>I am currently analysing data where the outcome variable is 'U' shaped. The outcome variable asks 'how many of the last seven days have you smoked'. Most responses to this fall in the first (none) and last (all seven) categories. Because of this I do not think a count data model is appropriate.</p>
<p>What would be... | 73,460 |
<p>We often face singular matrices in practice: OLS with singular (X'X), GMM with singular weighting matrix, singular matrix in Wald statistics. I'm wondering how can we overcome this issue. I've seen two solutions used in different contexts:</p>
<p>1) Ridge regression: <a href="http://en.wikipedia.org/wiki/Tikhonov_r... | 73,461 |
<p>I'm a fairly inexperienced statistician fighting a huge deadline and just need some peace of mind that I'm not making a massive error here. I'd be most grateful for pointers.</p>
<p>I've been playing around with different model combinations using the <code>lmer()</code> function, and have managed to get the AIC sc... | 73,462 |
<p>One of the often cited issues in RNN training is the vanishing gradient problem [1,2,3,4].</p>
<p>However, I came across several papers by Anton Maximilian Schaefer, Steffen Udluft and Hans-Georg Zimmermann (e.g. [5]) in which they claim that the problem doesn't exist even in a simple RNN, if shared weights are use... | 35,845 |
<p>I have two algorithms A and B, used to automatically classify each of N elements into K categories, N and K both being in the millions. Neither A or B is perfect, but it is relatively easy for a human to do the classification, or put another way, to select which one of the algorithms A and B did a better job for a g... | 73,463 |
<p>I have a space of 35 dimensions (attributes). My analytic problem is a simple classification one.</p>
<p>Out of 35 dimensions, more than 25 are categorical and each attribute takes more than 50+ types of values.</p>
<p>In that scenario, introducing a dummy variable also will not work for me.</p>
<p><strong>How ca... | 73,464 |
<p>While I was reading about Bayesian networks, I run into "<a href="http://en.wikipedia.org/wiki/Markov_blanket" rel="nofollow">Markov blanket</a>" term and got severely confused with its independency in a Bayesian network graph. </p>
<p>Markov blanket briefly says that every node is only dependent on its parents, c... | 35,849 |
<p>Essentially, I have some covariate data <code>X</code>, and a dependent variable <code>Y</code> consisting of proportions of a sample that shown a certain response (i.e. between 0 and 1). I suspect I want to proceed via a GLM approach, but the thing is, I don't know the sizes of each of those samples!</p>
<p>My tho... | 73,465 |
<p>Suppose I have 3 eggs, with independent hatching times (in minutes) following an $\text{Exp}(0.05)$ distribution, and A is defined as the earliest hatching time. <br> If I were to plot A, how would I explain its distribution? <br> From running a simulation on R, I can see that the histogram of A follows an exponenti... | 35,851 |
<p>I have a nominal and an ordinal variable and I would like to look measure the association that is between the two. For now, I have done Chi-square test and non-parametric Kruskall-Wallis Test and I have come to the conclusion that there is an association/relationship between the two variables. How can I further meas... | 73,466 |
<p>I'm currently training a support vector machine with a second order Markov transition matrix. These probabilities are taken from a computer image, and are the probabilities of adjacent pixels having the difference between them being specific values - so each value can be represented as a fraction $a/b$, where a and ... | 73,467 |
<p>Subject says it all - AR/MA/ARMA/ARIMA are often described as workhorses of time series analysis. But what are some real-world examples where these methods gave great results, and another more modern method wouldn't have been superior?</p> | 35,852 |
<p>I calculated a sequence of multi-level models with stata (xtmixed). I have a sample of 800 kids in 46 classes and I want to explain their individual level of prejudice by the proportion of fully prejudiced respondents in the class. This is based on a three categorical index, the level of prejudice is measured by a p... | 73,468 |
<p>I have about 3 hours worth of 3-axis accelerometer, gyroscope and compass data taken at subsecond intervals. I'm fully aware that this data needs to be filtered and that there are a shedload of methods for filtering it (FFT, ARMA, et al). How can I tell from my data or a plot thereof, which is the "best" filter to u... | 35,853 |
<p>I want to compare the <strong>delays</strong> of packets belonging to some kind of traffic to the delays of packets belonging to some other (different and larger) traffic, all generated from the same machine.</p>
<p>I would like to see if the <strong>distributions</strong> of the two groups of delays <strong>are th... | 73,469 |
<p>I know this is probably a basic question... But I don't seem to find the
answer.</p>
<p>I'm fitting a GLM with a Poisson family, and then tried to get a
look at the predictions, however the offset does seem to be taken into
consideration:</p>
<pre><code>model_glm=glm(cases~rhs(data$year,2003)+lhs(data$year,2003),
... | 73,470 |
<p>I'm trying to plot the predictions of a linear model with multiple numeric predictors as a collection of plots such that $\hat Y$ is on the y-axis, each $X_j$ in turn is on the x-axis, and the remaining $X_{i\ne j}$ are all set to plausible values given $X_j$. Here is some example R code (syntax might look strange, ... | 73,471 |
<p>I was told to run a changepoint analysis in R on my data. But the data shows a decreasing trend, so the changepoint analysis won't be of help (I don't think?). If I differenced the data, to get rid of the trend, and then perform a changepoint analysis on the differenced data, does that make sense? And how would I in... | 73,472 |
<p>I struggle performing a MANOVA for a mixed model. I have the following columns:</p>
<p>S - subject (1,...,N)
B - in between group (B1, B2)
W - repeated measurement - within (W1, W2)
M - measured dependent variable 1
N - measured dependent variable 2</p>
<p>My data is organized the following way:</p>
<pre><code>S;... | 73,473 |
<p>In SAS enterprise miner we have the optimal binning feature which allows you to transform continuous variables into an ordered set of bins. The binning, as I read from one of their docs, is done so that the log odds of the predicted categorical variable (good/bad) is monotonically increasing or decreasing. </p>
<p... | 35,858 |
<p>Is an implementation of a density function for a logit-normal distribution available in R?</p>
<p>I have not found one in a package or in the CRAN task view of probability distributions.</p>
<p>This is for a MLE fitting of a function to data.</p> | 35,861 |
<p>In ecology, we often use the logistic growth equation:</p>
<p>$$ N_t = \frac{ K N_0 e^{rt} }{K + N_0 e^{rt-1}} $$ </p>
<p>or</p>
<p>$$ N_t = \frac{ K N_0}{N_0 + (K -N_0)e^{-rt}} $$ </p>
<p>where $K$ is the carrying capacity (maximum density reached), $N_0$ is the initial density, $r$ is the growth rate, $t$ is t... | 73,474 |
<p>I have a couple questions about Cox survival regression:</p>
<p>1) Is it true that the hazard function h(t) is not available (even WITHOUT <a href="http://en.wikipedia.org/wiki/Time-varying_covariate" rel="nofollow">time dependent covariates</a>)- and if not, is it because the baseline hazard is not defined (only t... | 73,475 |
<p>From an answer in a <a href="http://stats.stackexchange.com/questions/24605/increase-the-sample-size-of-a-latin-hypercube-study">previous question</a>, I was directed toward the Halton sequence, for creating a set of vectors that covered a uniform sample space fairly evenly. But the <a href="http://en.wikipedia.org/... | 73,476 |
<p>I try to predict values for regression in LIBSVM. My data is in time series. I use gridregression.m file in LIBSVM to find optimal parameters c, g and p. Gridregression.m file use cross validation to find optimal parameters, but is it ok to use cross validation in time series? </p>
<p>When I use parameters from gri... | 73,477 |
<p>I ran an experiment and obtained the points shown in black below. </p>
<p>I would like to smooth the curve or fit (something like the red curve) in order to identify the elbow. </p>
<p>The problem is that the experiment is too expensive and there is a large amount of variance in the obtained points.
I tried fitti... | 47,272 |
<p>I have a large survey in which students were asked, among other things, their mother's level of education. Some skipped it, and some answered wrongly. I know this, because there a sub-sample of the initial respondents mother's were later interviewed, and asked the same question. (I'm sure there is some, smaller a... | 73,478 |
<p>Cohen's d is a measure of effect size calculated as:</p>
<p>$d = (x_1-x_2) / \sigma_{\text{pooled}}$</p>
<p>where $x_1$ is the mean of one group, $x_2$ is the mean of a second group, and $\sigma_{\text{pooled}}$ is the pooled standard deviation.</p>
<p>Let us say that one treatment has an effect size of 0.6 and a... | 73,479 |
<p>I am working on an assignment involving a logistic regression model, where I need to plot the pearson standardized residuals against one of the predictors. Here's the basic setup:</p>
<pre><code>model <- glm(outcome ~ predictor1 + predictor2, family=binomial(logit))
res <- residuals(model, "pearson")
</code><... | 35,871 |
<p>I am trying to derive the expression for the variance of $\hat{\beta_0}$ in simple linear regression. I substitute $\bar{y} - \hat{\beta_1} \bar{x}$ for $\hat \beta_0$, but in the intermediate steps the covariance term $\text{Cov}(\bar{y}, \hat{\beta_1})$ comes up and I don't know how to deal with it. Any help would... | 49,649 |
<p>I want to estimate $Y$ using different independent variables.</p>
<p>$$Y = d_1 + aX_1\\
Y= d_2 + bX_2\\
Y= d_3 + cX_3$$</p>
<p>Then I want to combine above 3 equations such that it gives the following relation:</p>
<p>$$Y = d + a_1X_1 + b_1X_2 + c_1X_3$$</p>
<p>How can I use the above 3 regression equations... | 73,480 |
<p>Let $\mathcal{E(h)}$ a function that given some hypothesis $h$ returns the generalization error for that fixed $h$.</p>
<p>I was reading some notes about model selection and generalization error and it said:</p>
<blockquote>
<p>"If we had access to $\mathcal{E(h)}$, there would be no model
selection problem ei... | 35,874 |
<p>Is there a way of using the linear model api to add the lasso penalty for a subset of the parameters I am regressing? For example, consider a linear separable decomposition that I want to fit to some sparse data subject to smooth constraints in one of the (separable) dimension.</p>
<p>This question indicates that t... | 35,875 |
<p>I have two questions. </p>
<p>1) If $X_1,X_2,X_3,...,X_n$ constitute a random sample of size $n$ from an exponential distribution, show that $\bar X$ is a consistent estimator of the parameter $\lambda$. </p>
<p>This is my attempt:<br>
Mean of exponential distribution is $\lambda^{-1}$. Thus by central Limit theo... | 73,481 |
<p>MaxDiff scaling is a very popular method for understanding customer preferences. I was wondering if we can create a survey questionnaire for MaxDiff analysis in R. Can anyone shed some light on this. </p> | 35,876 |
<p>I wish to run Permanova on categorical data (example CSV structure is below) without any successes. Is Adonis can handle categorical data, an example script will be great.</p>
<p>Thanks a lot</p>
<p>I have a this CSV file:</p>
<pre><code>Specie,Sex,Age,Location,Sensitivity
A,M,1,1,1
A,M,1,1,1
A,M,2,2,2
A,M,2,2,2
... | 73,482 |
<p>If you don't care about using GLM model parameters to predict anything, but simply want to select the best-fitting model for your data, is it necessary to get into the theoretical debate as to which link function to use? Is it OK to simply select the link function that gives you the lowest deviance? </p>
<p>Specifi... | 73,483 |
<p>Let $\hat{\Gamma}_k$ be the k dimensional sample autocovariance matrix. I am trying to prove this is nonnegative definite. The first step in the proof is to show that if $\hat{\Gamma}_m$ is nonnegative definite then $\hat{\Gamma}_k$ is nonnegative definite for all $k<m$. How do I prove this?</p>
<p>Many thanks i... | 73,484 |
<p>Suppose:</p>
<ul>
<li>$N \sim {\rm Poisson}(\lambda)$</li>
<li>$\lambda$ is unknown, but we believe that it can be assumed $\sim \exp(1)$</li>
</ul>
<p>If I want to calculate $N | X$, i.e., $P(model | data)$, I need to use the Bayes theorem in the following way:</p>
<p>$P(model|data) \propto P(data|model)*P(model... | 73,485 |
<p>I have a logistic regression model which predicts win/loss on amount of money paid. I run my model every two hours on new data that I acquire and use it to predict the next two hours. However, I keep finding that my model underpredicts win/loss for each amount of money paid. So I'm in this situation where I have a s... | 73,486 |
<p>Lets say I have three search engine e.g. search engine A, search engine B and search engine C.</p>
<p>Each search engine is given a set of queries Q (e.g. apple,banana,carrot....), this set Q remains the same for each engine.</p>
<p>Each engine then provides a set of results for each query in the form a SERP (sear... | 35,879 |
<p>Is it safe to do my one-hot encoding of categorical variables before splitting the data into training and test and cross validation sets? I ask because this process alters the dimension of the data, and it would be more complicated to get my test/cv sets into the same schema as the training set if they were one-hot ... | 73,487 |
<p>I am wondering which combinations of Naive models can be paired with different vectorizing methods so that it makes sense.</p>
<p>Let's say we have a simple binary spam-classification task.</p>
<h3>Multinomial model:</h3>
<p>If I understand correctly, the Multinomial model is used to calculate the class-condition... | 35,880 |
<p>Hi guys I am doing some model selection and need to estmiate both observed and expected Fisher Information Matrix to calculate this <a href="http://myweb.uiowa.edu/cavaaugh/ms_lec_4_ho.pdf" rel="nofollow">link</a>.
How do you estimate that expected one numerically? </p> | 31,095 |
<p>I've read that <strong>Mahalanobis distance</strong> is as effective as the <strong>Euclidean distance</strong> when <strong>comparing</strong> 2 <strong>projected feature vectors</strong> in classification using a <strong>LDA classifier</strong>.</p>
<p>I was wondering if this statement were true?</p>
<p>It would... | 35,881 |
<p>I have a set of measurements for web page response - 2356 6788 3658 5545 1008. How do i determine whether this set even bears evaluation / averaging. By manual inspection, this has no significance for me. </p>
<p>OR if I have a set like (1815 1856 1899 4567 1875), manually inspecting it i woul... | 38,331 |
<p>I have 50,000 objects on which I have performed two different types of regression. Using cross validation, I obtained the average $R^2$ score from each model on each of the objects. So now I have a list of 50k pairs of average $R^2$ scores. </p>
<p>I have used a paired Wilcoxon-Mann-Whitney U test and found that th... | 73,488 |
<p>Is it common practice (and adequate) to regroup two binary dependant variables into a single 4-level dependent variable to take advantage of the multinomial regression? For instance, say we have information on two related conditions (outcomes) A and B. A new 4-category variable would be defined such that:</p>
<pre>... | 73,489 |
<p>I'm implementing sentiment analysis on the set of user comments. All comments are on the same object. At the moment I decided to have three classes - negative, neutral and positive. I got test array of 1500 comments with marked classes. Tried to use SVM for classification on binary feature vectors in which each elem... | 392 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/16533/properties-of-logistic-regressions">Properties of logistic regressions</a> </p>
</blockquote>
<p>I have built a logistic regression model with two covariates. Let $y_i$ be the binary responses and $\... | 49,757 |
<p>In applying a penalty term with either $l_1$ or $l_2$ norm, why would the former result in variable selection but not the latter? </p> | 49,719 |
<p>In Section 2.4 of the book ESL by Hastie etc., it was said that $\hat{f}(x)=\text{Ave}(y_i\mid x_i\in N_k(x))\rightarrow E(Y\mid X=x)$ when $N, k\rightarrow \infty$ and $k/N\rightarrow 0$.</p>
<p>Here $N_k(x)$ is the neighborhood containing the $k$ points and "Ave" denotes average.</p>
<p>Is there a rigorous proof... | 73,490 |
<p>Performing a regression and need to find out if my residuals are normally distributed. </p> | 73,491 |
<p>I have three random variables, $X, Y, Z$. I know that</p>
<p>$$\log X - \log Y - \log Z = \log \frac{X}{YZ} \sim \mathcal{N}(0, \sigma^2)$$</p>
<p>How can I recover the distribution of $\frac{X}{YZ}$? Is it as simple as $e^{\mathcal{N}(0, \sigma^2)}$?</p> | 73,492 |
<p>I have the following test data:</p>
<p><img src="http://i.stack.imgur.com/NgRMv.png" alt="enter image description here"></p>
<p>How do I correlate the "believes" with "before" to determinate if it affects the "after"?</p>
<p>When believes is set to 1 the "after" will be (randomly) higher than when set to 0.</p> | 73,493 |
<p>I'm designing a neural network for binary classification problem in <code>MATLAB</code>. I have different number of inputs and samples in every problem ( I designed a software that end user will use it). I know that finding <code>number of neurons</code> and <code>layers</code> is a critical problem in neural networ... | 73,494 |
<p>I am interested in exploring how different characteristics of national pension systems are related to each other. I have used MCA for a dataset in which the rows are countries and the columns are different features of pension systems. However, I am not sure how to interpret the distances between points in the SPSS J... | 73,495 |
<p>I have a panel of daily stock prices $\{Y_{it}\}$, $t \in \{1,...,1000\}$ and some event that occurs at $t=700$ which causes the average stock price to decrease by about 10% over the next 15 days.</p>
<p>How do I answer the question "which stocks fell first"? I want to know of the characteristics of stocks that ten... | 73,496 |
<p>I'm using a Cox proportional hazards model, estimate the hazard rate for Levamisole relative to 5-FU, adjusting for Age and Sex.</p>
<pre><code>library(survival)
Colon<-subset(colon,etype==2 & rx!='Obs')
fitcox<-coxph(Surv(time,status)~rx+age+sex,data=Colon)
</code></pre>
<p>Now if I want to make some pr... | 73,497 |
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