question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I have been working on a project out of curiosity to get millions of URLs returned by search engines and save them to a text file or any other data source of mine.</p>
<p>with time my </p>
<p>I started my research by looking at Google Search API old one and new ones but they just returns you couple of hundred of U... | 35,061 |
<p>For an application, I want to cluster data (potentially high dimensional) and extract probability of belonging to a cluster. I consider at the moment Self organizing maps or kernel k-means to do the job. What are the pros and cons of each classifier for this task? Am-I missing others clustering algorithms that could... | 70,172 |
<p>A password consists of 4 alphabet letters and 4 numbers. Calculate the following two probabilities:</p>
<ol>
<li>$p_1$: the probability that the letters are all equal and that the numerical part contains one eight.</li>
<li>$p_2$: the probability that the password has 3 numbers followed by 4 letters.</li>
</ol>
<p... | 70,173 |
<p>I've got some data on discrete flood events (response variable - duration) on several rivers.</p>
<p>I've modelled the response variable by site and time using a Generalized Linear Model:</p>
<pre><code> mod = glm(duration ~ site + time)
</code></pre>
<p>I've then looked at the residual plots and cannot find any ... | 70,174 |
<p>Would it be true to say that Empirical Risk Minimization and M-Estimation are the same thing?</p> | 70,175 |
<p>Given a set of experimental data f={fk} for k=1,2,...,N, how can I find the best pdf which approximate the set fk? In the case of a gaussian distribution, applying the maximum likelihood criteria, it's easy to find the couple (μ,σ), but if I don't know anything about the distribution of the data, is the maximum like... | 41,418 |
<p>In our study which is completed, I have three groups: Drug A (n=87), Drug B (=62) and Drug C (n=5). The Shapiro-Wilk test, histograms and side-by-side box plots were used to assess normality of the data of the individual groups with respect to all the parameters used separately (weight, BMI, blood sugar, total chole... | 70,176 |
<p>I practiced some problem (not homework) as below.</p>
<p>Suppose that $X_1,X_2,\cdots$ are independent and identically distributed real-valued random variables with $E|X_1|=\infty$. Show that $\sum_{n=1}^\infty P({|X_n| \geq a\cdot n})=\infty$ for each $a >0$.</p>
<p>I obtained that $\infty = E(|X_n|) = \int_{0... | 30,965 |
<p>If I were to set up an experiment examining the effects of exercise, and coffee consumption on the number of hours slept, what would the be the ANOVA model that I should use, given: </p>
<ul>
<li>16 volunteers randomly assigned to two groups:
<ul>
<li>1st group will drink cup of coffee in the morning, </li>
<li>2... | 30,966 |
<p>Does anyone know of a large data set (upwards of $10^7$ rows, but I'll take $10^5$ as well) that would be appropriate for testing kernel logistic regression? Continuous variables, 2 to 50 independent variables? Would prefer business like data as aposed to scientific (weather, chemical, bio ...).</p> | 41,421 |
<p>My ultimate goal is to run a cluster analysis on a data set with > 1 million records. The input variables for the cluster analysis will be the results of a Principal Component Analysis, as well as other variables not included in the PCA, for a total of maybe 10 variables input into the clustering (the variables I in... | 70,177 |
<p>The title basically says everthing of importance. I read several times that a R2 is not used/interpreted if one is not using a constant. My question is: why? And if this statement is valid, I would be glad for valid source because I couldnt find one myself.</p> | 30,973 |
<p>I have a couple of quick questions about PCA: </p>
<ul>
<li>Does the PCA <em>assume</em> that the dataset is Gaussian? </li>
<li>What happens when I apply a PCA to inherently non-linear data?</li>
</ul>
<p>Given a dataset, the process is to first mean-normalize, set the variance to 1, take an SVD, reduce rank, an... | 30,975 |
<p>Suppose I have some data points (0.6695, 0.5968, 0.7641, 0.7252, and 0.7779) and want to fit different distributions to this dataset, say, log-normal and log-t (with different <em>df</em>), and then compare the tails of these distributions using graphics. How this can be done in R?</p> | 70,178 |
<p>Which distributions have closed-form solutions for the maximum likelihood estimates of the parameters from a sample of independent observations? </p> | 70,179 |
<p>I have a model in which two groups are measured on one DV at pre- post- and 3 months following an intervention (the control group did not receive the intervention). I have an interaction effect, which I believe implies that the combination of group and time together influence the DV, and yet the same SPSS ANOVA outp... | 70,180 |
<p>I have 40 "subjects", each of them did 5 types of exams.</p>
<p>The question I wish to test is if there is a difference in variance between the exams.</p>
<p>That is, I would like to run something like a "Bartlett's test", but for "repeated measures".</p>
<p>Does such a test exists?</p>
<p>Thanks.</p> | 70,181 |
<p>Markov chain Monte Carlo (MCMC) is a class of algorithms for sampling from probability distributions. In the end, given a parametric model explaining the data, MCMC could also be used for parameter estimation, in which case I wonder what the different options for processing MCMC samples are. For monomodal distributi... | 70,182 |
<p>Let's say I know the relation between <code>x</code> and <code>y</code> is linear yet noisy. Given a noisy <code>(x,y)</code> dataset is there a way to deduce if it was most likely generated out of an underlying function </p>
<p>(a) $y = a + b \times x + noise$
or via
(b) $x=c + d \times y + noise$</p>
<p>I'm no... | 70,183 |
<blockquote>
<p>There are $10$ empty boxes numbered $1, 2, \dots , 10$ placed sequentially on the circumference of a circle.We perform $100$ independent trials. At each trial, one box is selected with probability $\dfrac{1}{10}$ and one ball is placed in each of the two neighbouring boxes of the selected one.</p>
... | 30,978 |
<p>I am puzzled as to what specification I should include in my unit root tests of the following data: <img src="http://i.stack.imgur.com/kXSXg.jpg" alt="enter image description here">.</p>
<p>I will use ADF, KPSS and ZA tests. I can see there is a break in trend at observation 9. However, for the former two tests, es... | 70,184 |
<p>My questions are two fold:</p>
<ol>
<li>Is there a generally accepted statistic used to compare non-nested, nonlinear models with different numbers of parameters? I'm thinking RMSE, but wondering what other options might be?</li>
<li>I have a small dataset and am hoping to classify curves from it into three differe... | 70,185 |
<p>So, this is the question I'm working on:</p>
<p>Suppose we observe a random sample of five measurements: 10, 13, 15, 15, 17, from a normal distribution with unknown mean $µ_1$ and unknown variance $σ_1^2$. A second random sample from another normal population with unknown mean $µ_2$ and unknown variance $σ_2^2$ y... | 30,982 |
<p>I am trying to test if richness varies by treatment (Severity) over time (Block) using a repeated measures ANOVA in R. Any suggestions on how to do this correctly? I have tried, but get an error message stating I have an extra = in the formula:</p>
<pre><code>TWP.aov <- aov(Richness ~ Severity * Year + Error(Plo... | 37,947 |
<p>I can measure two variables on each patient in a survival study (I have the measurements and the survival times; some patients outlive the study and are therefore censored). I know that it is possible to use either of these variables to assign patients to groups with different survival curves (using a simple thresho... | 30,984 |
<p>I'm implementing a typical neural network with 1 hidden layer. The network does well with the logic XOR and other simple problems, but fails miserably when encountering a (16-input, 20~30 hidden, 3 output) training set. The problem is that the network does not learn anything, even with learning rate = 1.0 and moment... | 35,273 |
<p>One of my independent variables measures worker productivity through the variable $\frac{\log{sales}}{\text{# of workers}}$, and I'm creating one variable for skilled and another for unskilled workers. Past a point, as the number of skilled workers decreases there is a strong correlation with an increase in producti... | 98 |
<p>I am reading a lot about classifying optimization problems.
But i cannot find a real life example that treads the difference between
a stochastic and deterministic optimization problem.</p> | 70,186 |
<p>Suppose that $X$ and $Y$ are iid normally distributed and $a$ is a scalar. What is $\Pr(Y+aX<0 | X>0)$? </p> | 30,992 |
<p>I am testing an interaction effect where $X$ and $Y$ are continuous variable and $M$ (Moderator) is a categorical variable (effects coding $+1$, $-1$). </p>
<p>I have no clue about how to do a post-hoc probing of slopes in this case.</p>
<p>For a continuous moderator we calculate $Z_{\rm above}$ and $Z_{\rm low}$,... | 30,993 |
<p>I'm trying to select the best model by the AIC in the General Mixed Model test. The best model is the model with the lowest AIC, but all my AIC's are negative!</p>
<ul>
<li>So is the biggest negative AIC the lowest value?</li>
<li>Or is the smallest negative AIC the lowest value, because it's closer to 0?</li>
</ul... | 70,187 |
<p>I run the following 'experiment':</p>
<ul>
<li>take measurement x of observable</li>
<li>change one parameter</li>
<li>take measurement y of observable again</li>
</ul>
<p>I do this many times and want to test whether changing the parameter has an effect on my observables. More specifically, I want to test whether... | 30,995 |
<p>My book says that the exogneity condition, the condition that should hold in order for $b$ to be consistent, is the following:
$$\operatorname{plim}(\frac{1}{n}X'\epsilon)=0.$$</p>
<p>It then says that the $j$th component of this vector can be written as $\frac{1}{n} \sum_{i=1}^n x_{ji}\epsilon_i$, so that the cond... | 70,188 |
<p>I'm working with two independent normal distributions $X$ and $Y$, with means $\mu_x$ and $\mu_y$ and variances $\sigma^2_x$ and $\sigma^2_y$. </p>
<p>I'm interested in the distribution of their ratio $Z=X/Y$. Neither $X$ nor $Y$ has a mean of zero, so $Z$ is not distributed as a Cauchy. </p>
<p>I need to find the... | 37,500 |
<p>I'm a biologist, and I have a large dataset that I'm trying to analyze. Here are the variables I'm working with:</p>
<ul>
<li>levels of 211 different metabolites in 16 different blood samples (predictor variables)</li>
<li>how well each of the 16 blood samples performed in a specific test (response variable)</li>
<... | 30,998 |
<p>I have chemical compositions of individuals collected in 6 different sites in monthly intervals over a period of 6 months. </p>
<p>I would like to determine whether there is significant variation among sites as well as among months within sites. I was advised to use a repeated measures ANOVA to address this. Howeve... | 30,999 |
<p>I've been reading a number of articles and blog posts about issues relating to hypothesis testing. While these sources seem to put forth legit problems with hypothesis testing and it's interpretations, I'm not seeing anything in terms of alternatives to it (beyond bayesian hypothesis testing). What are some alternat... | 70,189 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/32864/how-to-get-sse-for-predictions-using-sas">How to get SSE for predictions using SAS?</a> </p>
</blockquote>
<p><img src="http://i.stack.imgur.com/oeRwA.png" alt="enter image description here"></p>
<p... | 49,845 |
<p>I have the following set of results for one of the factors (birth weight) with different levels and their corresponding Odds ratios for survival. I am using the first level (<1.25) as the reference level:</p>
<p>Birth weight (kg):</p>
<pre><code>Levels Number/level Odds Ratio
<1.25 1615 ... | 41,480 |
<ol>
<li>I wonder how a sequence of mutually independent random variables
(each with a different or same distribution) is sampled? In other
words, how can a sequence of values be ensured to be samples of a
sequence of independent random variables?</li>
<li>Furthermore how is a sequence of k-wise independent random vari... | 70,190 |
<p>I have 18 predictors in a binary generalized linear mixed model (repeated measurements, over a 1000 subjects). I would like to trim the model a bit and remove some noise and useless predictors. Unfortunately, <code>PROC GLIMMIX</code> does not have any facility to do this. I could not find an R package that would do... | 70,191 |
<p>I am doing a binary logit analysis, in which I'm trying to fit a model to my data to explain why some towns adopt open space subdivision ordinances (OP), using a handful of discrete and continuous independent variables. One of the explanatory variables, median household income, is coming back with an estimated beta ... | 31,002 |
<p>Are there any well-designed R packages or other open-source software for training Hidden Markov chains?</p> | 41,487 |
<p>I used a one-way ANOVA to test if importance levels of attributes have changed over the years (Data comes from a survey of consumers) with the following results (Mean ratings):</p>
<pre><code>+-----+---------+
| Year|Attribute|
+-----+---------+
| 2000| 4.39|
+-----+---------+
| 2010| 4.30|
+-----+---------... | 969 |
<p>Folks,
I am working on a credit card defaults and transition probabilities. For example a single credit card account could be in a number of states: up-to-date, 30, 60, 90 days in arrears or in default.</p>
<ul>
<li>Are there packages in R that do estimation of the transition probabilities given historical monthly ... | 31,004 |
<p>Suppose we have the following Cox Model: $$g(t,d,x ,\beta) = \ln[h_{0}(t)]+d_{1}\beta_{1}+d_{2}\beta_{2} + d_{1}d_{2} \beta_{3}$$ where $d_1$ and $d_2$ are binary variables that take $1$ or $0$. What is the difference between the following hazard ratios:
$$\exp(\beta_{1}+\beta_3)$$
$$ \exp(\beta_1+\beta_2 +\beta_3)$... | 70,192 |
<p>Sorry if this seems incredibly basic, I tried to do some reading but I'm getting a bit confused.</p>
<p>I have 12-dimensional data, sampled from 10 different populations. I want to know if these populations are significantly different from each other, taking into account their means and standard deviations. Is ther... | 70,193 |
<p>Cox Proportional Hazards models are traditionally taught alongside proportional hazards assumptions. There is a corresponding test of proportionality. However, if standard errors are calculated from sandwich estimators, there's no need to worry about that assumption, you just interpret the hazard ratio you DO obtain... | 31,006 |
<p>After I remove these 4 observations, the results change from weak and not statistically significant to the opposite (rho=0.559 with p<0.01). Should I just remove them or what should I do? Although the Spearman correlation is robust against outliers, can I call these observations outliers? If so, how should I deal... | 31,008 |
<p>Let's say I have two samples and I want to calculate confidence intervals for the means of each sample.</p>
<pre><code>x = rnorm(10)
y = rnorm(10)
</code></pre>
<p>Using the t.test command I'm able to get the following output.</p>
<pre><code>> t.test(x, y)
Welch Two Sample t-test
data: x and y
t = -0.01... | 70,194 |
<p>When using <code>libsvm</code>, the parameter $\gamma$ is a parameter for the kernel function. Its default value is setup as $\frac{1}{Number Of Features}$ </p>
<p>Is there any theoretical guidance for setting up this parameter besides existing methods, e.g., grid search?</p> | 46,700 |
<p>I have two sets of responses from two different sensors. In each set, the first column is distance measured in feet, and the second column is the response of the sensor. Sensor A has response values in the 10-20 range, with very low variance, and Sensor B has responses in the 50-1000 range, with higher variance, ove... | 70,195 |
<p>I am a doctoral student in clinical neuropsychology, and am in the process of creating z-unit weighted composite scores based on a battery of ability tests (i.e., attention/executive functions composite = Z scores for Trails A&B, Stroop, Digit span, RBANS coding, Symbol search). The scores will be used in a reg... | 656 |
<p>I want to decide which are the most relevant attributes for clustering algorithms.</p>
<p>My dataset has attribute this way: </p>
<pre><code> DBSCAN(data[latitude, Longitude, att1, att2, att3, att4, att5] )
DBSCAN(data[att1, att2, att3, att4, att5] )
</code></pre>
<p>What metrics should I use in this case ? S... | 33,109 |
<p>I am trying to move from using the <code>ez</code> package to <code>lme</code> for repeated measures ANOVA (as I hope I will be able to use custom contrasts on with <code>lme</code>).</p>
<p>Following the advice from <a href="http://blog.gribblelab.org/2009/03/09/repeated-measures-anova-using-r/">this blog post</a>... | 70,196 |
<p><a href="http://en.wikipedia.org/wiki/Mean">Wikipedia</a> explains:</p>
<blockquote>
<p>For a data set, the mean is the sum of the values divided by the number of values.</p>
</blockquote>
<p>This definition however corresponds to what I call "average" (at least that's what I remember learning). Yet Wikipedia on... | 70,197 |
<p>I was wondering how to create a vector with equivalent spacing between its consecutive elements in R? In Matlab, I can do [start:step:end].</p>
<p>Also if I want to plot a function with analytical form, do I have to evaluate the function on some sample points in its domain and plot these pair of points? Is there a ... | 70,198 |
<p>I am studying intervention analysis in time series with the Cryer and Chan <a href="http://homepage.stat.uiowa.edu/~kchan/TSA.htm" rel="nofollow">book</a> and am looking at trying to understand how to code the step response interventions. One question I had is how to differentiate between these two models:</p>
<p><... | 24,249 |
<p>I believe that some variables can be interval/ratio or ordinal based on the context. I'd like to know people's opinion on this. Let me explain:</p>
<p>Class variable with categories Freshman, Sophomore, Junior, Senior. Seems like an ordinal variable right? Well, a student's class standing is determined by credits. ... | 70,199 |
<p>I conducted a study in which two groups of teachers (pre-service and veteran) all watched four video clips of instances of aggression between students. The clips differed by type of aggression and gender of the students depicted (physical vs. relational aggression; male vs. female). After viewing each clip, the pa... | 70,200 |
<p>Suppose under $H_1$, $X_i$'s are independent random variables with $\mathrm{Poisson}(\theta_i)$. Under the null hypothesis, $X_i$'s are IID from $\mathrm{Poisson}(\theta)$.</p>
<p>Define pearson chi square statistic as: $\sum_{i = 1}^{n} \frac{(X_i - \bar{X})^2}{\bar{X}}$. How can I derive the asymptotic distributi... | 31,023 |
<p>This is a general question about how the L-BFGS-B optimization algorithm works. </p>
<p>I have encountered some strange likelihoods in a model I was running (which uses optim from R, and the L-BFGS-B algorithm). The function optimizes over a parameter, which is constrained to 0-1 and maximizes the likelihood (Minim... | 31,024 |
<p>My experiment is devised as follow: There are two different types of stimuli-- cellphones: android (android-1; android-2) and iOS (iOS-1 and iOS-2). A sample size of 60 subjects are divided into two groups of Group A:30 - Group B:30. The first group (Group A: 30) is further divided into two groups of (GroupA1- 15 a... | 70,201 |
<p>I am just wondering - is there a name for these kinds of graphs? The associated text that comes with the graph says the following:</p>
<p><img src="http://i.stack.imgur.com/PFRBn.png" alt="enter image description here"></p>
<blockquote>
<p>Figure 2 presents a view of the distribution of correctable errors
over... | 31,025 |
<p>I have a sequence of numbers that grows super-exponentially:</p>
<pre><code>0.993, 0.999, 1.037, 1.054, 1.195, 1.55, 2.953, 15.369, 815.687, 26492.118
</code></pre>
<p>I'd like to be able to plot the data in such a way that the viewer will be able to tell how the whole sequence increases: for my application, the f... | 49,540 |
<p>I have a small pet project, which evolves around predicting a radar image of rain clouds given past radar images...</p>
<p>My data comes from the radar images on following site:<br/>
<a href="http://www.dmi.dk/vejr/maalinger/radar-nedboer/" rel="nofollow">http://www.dmi.dk/vejr/maalinger/radar-nedboer/</a><br/>
(ra... | 31,027 |
<p>I'm looking to manually (Excel) perform PCA without any statistical packages such as R, but having trouble understanding how to rotate the original variables to find the maximum variance for the new Factors.</p>
<p>My understanding is that for two variables the formulas are:
x1* = cos() x1 + sin() x2
x2* = - sin() ... | 70,202 |
<p>Below is the report of my out-of-bag <code>precision</code>, <code>recall</code> and <code>f-1score</code> when using <code>scikit-learn</code></p>
<pre><code> precision recall f1-score support
pos 0.72 0.47 0.57 97929
neg 0.61 0.82 0.7... | 70,203 |
<p>I am trying to design a matrix factorization technique for a simple user-item, rating recommender system. I have 2 questions about this. </p>
<p>First in a simple implementation that I saw of matrix factorization technique for movie recommendation, the author just initialized the dimensions of the latent features l... | 70,204 |
<p>I'm currently working with some measurements of the following form: </p>
<ul>
<li><p>Three test subjects, three trials per test subject, three measurement points per trial:</p></li>
<li><p>At each measurement point within each trial, I have time measurements and velocity measurements, each with associated +/- error... | 31,028 |
<p>I'm looking for a general, clean and fast (i.e. using C++ routines) R package for simulating paths from a non-homogeneous nonlinear diffusion like (1) using the Euler-Maruyama scheme, the Milstein scheme (or any other). This is destined to be embedded into a larger estimation code and therefore deserves to be optimi... | 70,205 |
<p>Consider the nonlinear mixed effects model for the $j$th observation $y_{ij}$, $j=1,\dots,n_i$, $i=1,\dots,N$, of individual $i$ at time $t_{ij}$ :
$$
y_{ij} = f(\alpha_i, t_{ij}) + g(\alpha_i, t_{ij}) \varepsilon_{ij}.
$$
Here $\alpha_i$ is the random effect, $\alpha_i \sim \mathcal{N}(\mu,\Sigma)$ and $\varepsil... | 70,206 |
<p>Between the two data mining software, which is easier to use: WEKA or RDS (Rule Discovery System)?</p>
<p>What are the pros and cons of both software?</p> | 70,207 |
<p>Is it possible to estimate a tobit model (e.g. a nonlinear model) with a DiD (difference-in-differences) specification? If so, how does such specification look like? </p>
<p>If it is possible is this implemented in R or Stata?</p>
<p>Comment: @Dimitriy V. Masterov: Thanks for your answer! Would this still work if... | 70,208 |
<p>Statistical modeling is new to me and I would appreciate some thoughts on my project. I am trying to model the spatial (and possibly temporal as well) relationships within vectors in vector fields. Just for the sake of background, each vector field is a collection of motion vectors that corresponds to a compressed H... | 31,030 |
<p>In OLS regression, what does a one unit change in X represent in terms of a beta-related change in Y when the outcome variable has been transformed to $1/\sqrt(Y)$? </p>
<p>(Transformation was done to ensure linearity in the model. My predictor variables are 0-1 dummies.)</p>
<p>I've consulted the following useful... | 70,209 |
<p>I am learning about machine learning <a href="http://scikit-learn.org/stable/auto_examples/applications/plot_stock_market.html" rel="nofollow">here</a>.</p>
<p>They took a set of prices for specific companies on the stock market and graphed them:</p>
<p><img src="http://i.stack.imgur.com/rsC5t.png" alt="enter imag... | 70,210 |
<p>I am running a survival analysis with descrete time. For that purpose I use the R package <code>survival</code> with this function</p>
<pre><code>surv.km <- survfit(formula = Surv(analyse$Time, analyse$Event) ~ 1, conf.type = "log",
conf.int = 0.95, type = "kaplan-meier", error = "greenwood", data = analyse)
<... | 37,342 |
<p>Given $X\sim{\cal N}(\mu_X,\sigma^2_X)$, $Y\sim{\cal N}(\mu_Y,\sigma^2_Y)$ I am looking for the p.d.f. of $\operatorname{atan2}(Y,X)$ where $\operatorname{atan2}()$ is the 4-quadrant arc tangent. Does this distribution have a name? Is there any literature about it?</p> | 70,211 |
<p>Is there any technical trick to determine the third quartile if it belongs to an open interval which contains more that one fourth of the population (so I can't close the interval and use the standard formula)?</p>
<h3>Edit</h3>
<p>In case I misunderstood something I will provide more or less full context. I have ... | 37,867 |
<p>I'm using an lmer on a set of continuous data. <a href="http://stats.stackexchange.com/questions/33709/interpreting-the-regression-output-from-a-mixed-model-when-interactions-between">This post</a> helped me a great deal when interpreting results, as I have two conditions and three levels as well, but I've run into ... | 70,212 |
<p>I am looking to model physical activity (in minutes) as my dependent variable. I have several independent variables of the environment around the school (intersections, traffic, etc). </p>
<p>What type of model would make sense? I was thinking multiple linear regression but some of the variables do not really ha... | 70,213 |
<p>On a post from the internet I've found the following expression, which I'll like to understand and to apply it on my datas. </p>
<blockquote>
<p>"Because of the size difference between the largest and the smallest
metros, the data is expressed in logarithmic form so as to facilitate
comparison."<a href="http:... | 41,539 |
<p>I've conducted an experiment in which we have registered a physiological measure (FR) of 30 participants in two different conditions. In each condition, I registered the measure in 20 time points, equally spaced in time. </p>
<p>To analyze the data, I'have fitted a multilevel model in R, using the nlme package. I'v... | 109 |
<p>I am a little bit confused by the distinction. What are the formal definition of paired and unpaired? More specifically, if I have 2 time series measuring the same quantity (e.g. vacancy rate) with slightly different underlying data, are the data paired or unpaired?</p> | 31,036 |
<p>I'm confused about how to calculate the perplexity of a holdout sample when doing Latent Dirichlet Allocation (LDA). The papers on the topic breeze over it, making me think I'm missing something obvious...</p>
<p>Perplexity is seen as a good measure of performance for LDA. The idea is that you keep a holdout sample... | 41,540 |
<p>These coefficients look way too large to me, they seem to imply probabilities of around 0.5, instead of around .01, as I would expect.</p>
<p>Here is sample code:</p>
<pre><code>set.seed(1L)
ids <- as.factor(rep(1:10,rep(10,10)))
ps <- rnorm(n=10,mean=0.01,sd=.002)
ns <- sample(500:2000,replace=T,size=100... | 41,541 |
<p>Im using <code>RandomForestClassifier</code> for a probability prediction task. I have a featureset of around 50 features and two possible labels - <code>first team wins</code> and <code>second team wins</code>.</p>
<p>The feature set contains features for both teams, and the way I built it, since I know which team... | 70,214 |
<p>I have a dataset of cases and age & sex matched controls (n=25). I need to do a statistical test to find the significantly different incidences of ICD-9 codes using a p-value or similar measure. </p>
<p>What test should I use in this scenario and how should I define significance ? Given the low number of sample... | 31,038 |
<p>I will try to be as clear as I possibly can:</p>
<ul>
<li>I want to populate a matrix of about 10 million rows by 43 columns as a test to an application</li>
<li>The first task is to generate a random number around 10 million</li>
<li>Second I need to fill out the columns. Let's say for column 2, random ints can on... | 41,543 |
<p>I run <code>caret</code>'s recursive feature selection with randomForest. While running <code>rfe</code> function with method repeatedcv, I had parameter maximize = TRUE. Thus, optimal set of variables is decided based on the best RMSE metrics. </p>
<p>However, I would like to see the minimum "tolerable" set of pre... | 31,040 |
<p>I have a nuclear family consisting of dad, mom, me and my younger sister. Our birth week i.e. week in which we were born are linear according to our date of birth i.e. my father who is oldest was born on wednesday, my mom on thursday, me on friday and finally my sister(who is youngest) on saturday. </p>
<p>When i w... | 70,215 |
<p>I am a programmer and trying to do some data analysis. Since I am very interested in statistics, and I have learned a <strong>lot</strong> of programming languages, learning how to use professional packages such as MATLAB, R or numpy etc. will be a waste of time (because I might not be using these all the time). I ... | 665 |
<p>I have a system with two components, component A and component B. Let $X$ be the random variable representing time between failures of component A and $X$ is exponentially distributed. Let $E[X]=m$. Now we want to test the following hypothesis:</p>
<p>null hypothesis: $m\le m_0$ where $m_0$ is some given constant
a... | 31,042 |
<blockquote>
<p>Blockquote</p>
</blockquote>
<p>$Y= X_{i}\beta +Z_{i}b_i +\epsilon_i $</p>
<p>where $\epsilon_i \sim \mathcal{N}(\mu, \sigma)$</p>
<p>and $b_{i} \sim \Gamma$</p>
<blockquote>
<p>Blockquote
what is the distribution of Y when i do this mixture and is it easy to sample
from it
Blockquote</... | 70,216 |
<p>This is a question from a data mining exam:</p>
<p>You are working with a dataset that contains descriptions of toxic and non-toxic substances.</p>
<p>The dataset, which consists of 1000 examples from each of the two classes, is described in terms of a class label and a number of attributes. The dataset is sorted ... | 31,046 |
<p>I'm about to use the glm() function in R, and I know that I have to specify which family of variance/link functions I want to use (either gaussian, binomial, poisson, Gamma, inverse.gaussian, or quasi-which I take to mean user-defined). I understand that binomial is to be used for things like logistic regression, bu... | 70,217 |
<p>Suppose that people arrive at a location $l_1$ and move to a nearby location $l_2$ at various points in time. We are interested in modelling the transition from $l_1$ to $l_2$. We suspect that the transitions follow an exponential distribution with parameter $\lambda$, and that people transition independently with ... | 70,218 |
<p>I am going to conduct a survey in order to collect information for two variables and then calculate the correlation between them.</p>
<p>If we assume that $alpha$ = 0.05, $power=0.80$. Can someone show me a step by step method of how a sample of 85 was determined with a medium effect size? And is there a procedure ... | 31,047 |
<p>Could anyone kindly provide an explanation (mathematically or non-mathematically) about the non-existence of the intercept term in <a href="http://www.ats.ucla.edu/stat/sas/library/logistic.pdf" rel="nofollow">conditional logistic regression</a>? Is the interpretation of the coefficients similar to that of (uncondit... | 70,219 |
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