question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I was watching <a href="http://youtu.be/IuRb3y8qKX4?t=3m39s" rel="nofollow">this</a> tutorial on K-means clustering and from what I understand K-means is:</p>
<ol>
<li>Randomly generate the centroids for k clusters</li>
<li>Create a classification model dividing into k regions (Do we use kNN here?).</li>
<li>Genera... | 70,617 |
<p>I'm trying to find a way to visualize the results of an association analysis where I corrected for confounding variables.</p>
<p>I have a set of cytokine data (amount of protein in the blood) from a set of patients infected and uninfected with HCV. The difference between the two is minimal when we test/visualize th... | 70,618 |
<p>I thought I would write this to <a href="http://stackoverflow.com/">Stack Overflow</a>, but LaTeX Math is not working there. I am trying to program the following equation in R: </p>
<p>$\hat{\sigma}^2=1/n\sum_{i=1}^{n}[\int \hat{K}(u)\sum_{i=1}^{n}W_{1i}(u)\{dN_{1i}(u)-\hat{\lambda}(u)Y_{1i}(u)du\}]^2+1/n\sum_{i=1}... | 70,619 |
<p>I know that $\frac{1}{n-1}\sum_{i=1}^{n}(X-\bar{X_{n}})^{2}$ is an unbiased estimator for the variance.</p>
<p>I thought of such an estimator to be useful when it is not know from which distribution the data at hand are coming from.</p>
<p>Now given I have a data set and I do know which is the underlying distribut... | 70,620 |
<p>Does anyone have any good references comparing suitability / stability of different extraction methods for exploratory factor analysis on binomial variables?</p>
<hr>
<p>I have had a search on-site and internet search but i have only been able to find one 20 year old paper on WLS extraction, which is still good. I... | 70,621 |
<p>I'm using R and have two vectors of discrete values. They are not strictly speaking categorical because the values themselves are number of dots counted on the image of a cell (whole vector is all the cells on the image). There are two vectors: reference and a vector with dot counts after some perturbation</p>
<p>W... | 70,622 |
<p>I have a data set of presidential election results for the past 33 elections. I threw out everything pre 1972, however, because of the structural changes that occurred through the decades, and because I am assuming a degree of auto-correlation in the data, so I want to get rid of previous trends that are not materia... | 70,623 |
<p>In a RCT we would like to compare oncological outcome of two surgical 2-stage strategies, i.e. patients require to undergo both stages to become free of cancer.
The problem is that strategy A generally takes less time to come to the second stage becoming free of cancer.
On the other hand, in strategy B some patients... | 70,624 |
<p>In several situations, I have two unbiased estimators, and I know one of them is better (lower variance) than the other. However, I would like to get as much information as possible, and I would like to do better than throwing out the weaker estimator.</p>
<p>$$\newcommand{\Outcome}{\text{Outcome}}\newcommand{\Skil... | 70,625 |
<p>How does one simulate data for a path model? Below is an example path model with parameters b1, b2, b3, b4, b5, e1, e2 and e3. </p>
<p>I would like to investigate how sample size affects my estimates and what happens to the estimates if a path is added or removed.</p>
<p><img src="http://i.stack.imgur.com/Sj5t7.... | 70,626 |
<p>I'm looking for a translation to either English, French or German of Kolmogorov's Russian paper</p>
<p><em><a href="http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=im&paperid=3752&option_lang=eng" rel="nofollow">Kolmogorov, A. (1942). Sur l’estimation statistique des paramètres de la loi de Ga... | 42,238 |
<p>What is most efficient way to updating cholesky factorization of for removing a column from the matrix?</p>
<pre><code>T = Chol(X' *X)
</code></pre>
<p>If I remove a column from X, how to effienciently update cholesky. It is trivial to remove the last column of X as new cholesky will be removing last row and colum... | 70,627 |
<p>I am performing distributed non-linear lag models in R.</p>
<p>I got the figure result of <code>dlnm</code> as shown in the vignette (<a href="http://cran.r-project.org/web/packages/dlnm/vignettes/dlnmOverview.pdf" rel="nofollow">pdf</a>) on page 13: </p>
<p><img src="http://i.stack.imgur.com/Qjf7B.png" alt="ente... | 70,628 |
<p>I'm trying to say something about sales of candy bars. I got data on sales for a population of children. There are three factors: age, income of parents, and name of a child. </p>
<p>What I can compute from this data is, say, that 34% of all sold candy bars were bought by children of age 12, 25% by children of age ... | 70,629 |
<p>I'm using the <code>caret</code> package in <code>R</code> that provides two kind of metrics for classification problems - accuracy and kappa. When should I prefer one over another?</p> | 70,630 |
<p>When feeding a categorical variable into <code>glmnet</code> do I code <code>n</code> or <code>n-1</code> dummy variables?</p>
<p>For instance if using days of the week as an independent variable would I use 6 dummies or 7?</p>
<p>If the answer is 6, how do I interpret coefficients, etc for dropped category?</p>
... | 70,631 |
<p>In my mind, the commands <code>logit</code> and <code>glm</code> (Binomial family) in <code>Stata</code> both use maximum likelihood estimation, and the ML estimates and SE values are the same. But one instructor stated that they use different fitting/estimation algorithm. So I would like to hear the difference.</p> | 31,688 |
<p>Coming from <a href="http://stackoverflow.com/questions/1232615/compute-statistical-significance-with-excel">this</a> post, but their question wasn't fully answered.</p>
<p>I understand how the t-test works – if I have two sets of data and want to see if one is better (or worse) than the other, I would say <code>tt... | 70,632 |
<p>R glm and glmnet use different algorithms. </p>
<p>I notice non trivial differences between the estimated coefficients when I use both.</p>
<p>I am interested in when one is more accurate than another, and the time to solve/accuracy trade off.</p>
<p>Specifically I am referring to the case where one sets lambda=0... | 48,842 |
<p>I'm doing a multilevel mixed model with three cross-level interactions in LMER. Do all three interactions necessarily need to be included in the same model or can I evaluate them in three separate models? </p> | 31,691 |
<p>I´m doing multivariate modeling on a dataset where the dependent variable is ordinal-values running from 0-11. So far I´ve done general linear models and it runs alright. However, I´d also like to run it as an logistic ordinal regression. </p>
<ul>
<li>What is the recommended maximum number of categories in the dep... | 42,250 |
<p>I have a rather simple problem that I'm having trouble deciding an answer upon. As a student studying Statistics I'm very familiar with terminology and theory but I suppose I'm stumped on my first real application of classroom teachings.</p>
<p>I have data on the size of database uploads that occur everyday. The da... | 49,496 |
<p>Suppose that I have a series of $M$ time-observations of $N$ "quantities" $z_1(t_1),...,z_1(t_M)$, ..., $z_N(t_1),...,z_N(t_M)$. I want to estimate the values of $z_1(t_{M+1}),...,z_N(t_{M+1})$. This a problem of interest, for example, in stock asset prediction. I want to use Principal Component Analysis (PCA) perfo... | 70,633 |
<p>I'm exploring the use of changepoint detection or other methods (am slowly becoming aware of wavelet transformation, etc. but have tons to learn in this area) to identify key shifts in health care performance patterns over time. However, many of the metrics I'm seeking to analyze (e.g., health care quality metrics) ... | 70,634 |
<p>I find that there are two ways to calculate AIC:</p>
<p>AIC = -2ln(likelihood)+ 2K and<br>
AIC = n*ln(RSS/n)+2K</p>
<p>I have:</p>
<pre><code>crf <- c(0.3333333, 0.5000000, 0.6666667, 0.6666667, 0.6666667, 0.8333333, 0.1666667, 0.3333333, 0.5000000, 0.5000000, 0.8333333, 0.5000000,0.6666667, 0.5000000, 0.66666... | 70,635 |
<p>In a <a href="http://stats.stackexchange.com/questions/21078">previous</a> question I was trying to figure out how to compute the confidence interval of a ratio. Having come to the conclusion that the correct way to do this is <a href="http://en.wikipedia.org/wiki/Fieller%27s_theorem" rel="nofollow">Fieller's Theore... | 6,059 |
<p><strong>Introduction:</strong></p>
<p>I am currently doing some reading on psycological research and in this context I have some questions which may seem very simple. Nevertheless, it is not very transparent from the articles how the calculations are made so please feel free to answer as broad or as specific as you... | 70,636 |
<p>I am trying to fit either the <code>coxph</code> or <code>survreg</code> function with the <code>Survival</code> package. </p>
<p>I would like to specify my Hazard functional form as:</p>
<p>$H(t) = exp\{ (\beta_0) + (\beta_1)*X_t +(\beta_2)*log(X_t)\}$.</p>
<p>Is the way to specify it into my model as just strai... | 70,637 |
<p>I ran a hierarchical negative binomial regression analysis, and got information relative to the log likelihood and likelihood ratio chi-squared in the output. I have the following questions regarding the goodness of fit:</p>
<ol>
<li>What model is preferred? I heard the one with the log likelihood closer to zero in... | 70,638 |
<p>I have data which describe measurments in four different point for few days.
Four water parameters have been measured.
In other words, data contains following columns:</p>
<ol>
<li>point name - we have four points names, of course this value is not unique for each row (as we have few measurment for few days)</li>
<... | 42,256 |
<p>In my research there is a pretest, and a treatment followed by a posttest.
The pre and the posttests are similar but not exactly the same. A few questions were changed between the pre and posttests to avoid sensitizing the students to the questions in the pre-test, which might affect the internal validity of the st... | 70,639 |
<p>I'm having trouble understanding the output of my <code>lmer()</code> model. It is a simple model of an outcome variable (Support) with varying State intercepts / State random effects:</p>
<pre><code>mlm1 <- lmer(Support ~ (1 | State))
</code></pre>
<p>The results of <code>summary(mlm1)</code> are:</p>
<pre><c... | 6,061 |
<p>First - very new to Statistics; about half through a basic biostats book and an R book. </p>
<p>I have a set of data where I"m trying to see if there is a correlation between a medication and weight gain. The dataset: </p>
<ol>
<li>~2200 patients</li>
<li>A list of their primary diagnoses, weight, date's of visit,... | 31,695 |
<p>I have been asked to "construct a (normal) QQ plot" for a set of numbers. However it is not a set of pairs or a pair of sets, just a single set of numbers.</p>
<p>If we go ahead and assume the second probability distribution is the normal distribution, how would I go about satisfying this request?</p> | 31,696 |
<p>Just wondering if anyone is familiar with clustering nominal inputs. I've been looking at SOM as a solution but apparently it only works with numerical features. Are there any extensions for categorical features? Specifically I was wondering about 'Days of the Week' as a possible features. Of course it is possible t... | 31,697 |
<p>My goal is to quantify dosage impact on cure probability for different patients. Let's suppose I have N patients with their charateristics such as age, gender, weight.... Also let's assume there is a known range for dosage, say from 0 to 1. </p>
<p>Here is what I'm currently doing:</p>
<ol>
<li>Randomly split all ... | 70,640 |
<p>I want to do price modeling using the Van Westendorp price sensitivity meter. </p>
<p>Can anybody provide me resources describing how to do this using R?</p> | 70,641 |
<p>I need some suggestion for clustering (unsupervised classification) method for a consulting project. I am looking for a method that hopefully has the following properties:</p>
<ol>
<li><p>The subject of my study has three properties. One is represented by
a (non-Euclidean) distance matrix and the other two are in t... | 31,701 |
<p>We are building a score card system to measure the performance of various groups in the organization. The scores are generated by true / false metrics on individual transactions that each group completes.</p>
<p>Transactions are qualified for measurement by some metrics but not others. The number of transactions ... | 70,642 |
<p>I have observations of four different groups of people. The dependent variable are count data (medical emergencies in the past 2 months). For each group, the dependent variable follows a negative binomial distribution with a maximum at 0. Now I would like to examine, if the factor "group" (meant to be categorical) i... | 70,643 |
<p>When using bootstrapping for model evaluation, I always thought the out-of-bag samples were directly used as a test set. However, this appears not to be the case for the <a href="http://scikit-learn.org/0.14/modules/generated/sklearn.cross_validation.Bootstrap.html">scikit-learn bootstrap function</a>, which seems t... | 10,063 |
<p>I need to calculate matrix inverse and have been using <code>solve</code> function. While it works well on small matrices, <code>solve</code> tends to be very slow on large matrices. I was wondering if there is any other function or combination of functions (through SVD, QR, LU, or other decomposition functions) tha... | 98 |
<p>The table below is extracted from <a href="http://en.wikipedia.org/wiki/Pollutant_Standards_Index" rel="nofollow">Wikipedia</a>. It shows the Pollution Standards Index (PSI) readings of Singapore.</p>
<p><img src="http://i.stack.imgur.com/Qgmmv.png" alt="enter image description here"></p>
<p>I am trying to estimat... | 70,644 |
<p>I often need make $(x,y)$ scatter plots that have many ($>10^5$) points. I've experimented with different ways of representing this many points that capture the distribution while getting around the messiness of actually putting a million points in an image. I've done the obvious things like thinning points, and ... | 70,645 |
<p>I am working on a classification problem using IP addresses as input and I am trying to find which IP addresses or subnets are likely to belong to a spammer. I have data consisting of the four octets in the IP address as well as a label: SPAM or OK.</p>
<p>This feels like a good problem for a decision tree, but I a... | 31,706 |
<p>I want to joint 4 Poisson variables and 1 Bernoulli variable with D-vine copula. How can I do this with R?</p> | 31,707 |
<p>I am trying to implement a noncentral <em>t</em> CDF as expressed by Guenther (1978), Lenth (1989), and the Wikipedia article on the non-central <em>t</em> in R. I have got my algorithm half working: when the signs of <em>t</em> and Delta are equal, I get identical results to R's pt(), but when the signs are opposit... | 70,646 |
<p>I am using 1983-2008 annual data to test if both gini coefficients and gross national saving in China and the US can affect the US current account balance. The data seem to be non-stationary, but I am a beginner and only knows the basic multiple regression model and autoregressive distributed lag model, can I still ... | 70,647 |
<p>I was wondering what are the implications of using a <strong>multi-class Naive Bayes</strong> versus a <strong>2 class Naive Bayes</strong> (for one against everything).</p>
<p>Which technique performs <strong>better</strong>? </p>
<p>I've previously came across an instance where <strong>2 class LDA classifier</st... | 70,648 |
<p>Is there a canonical way to do degrees of freedom (DF) correction to <code>ols</code> objects from the <code>rms</code> package (and to <code>lm</code> objects in general)? I am demeaning my data then running a pooled regression instead of using indicator variables and realizing there's a lot that I don't understand... | 70,649 |
<p>I am trying to figure out how to run a GLM with a poisson distribution in R. The data has 4 treatments: $\text{A}(n=16)$, $\text{B}(n=17)$, $\text{C}(n=16)$, $\text{D}(n=20)$, and 2 time periods. This data is count/area so there are decimals. Ultimately, I would like to know if there are differences between the tr... | 70,650 |
<p>Consider an MA(1) process, $d_{t}=e_{t}-\Theta e_{t-1}$, when $d_t$ is the demand at time $t$ and $e_t$ is error term and $\Theta$ is moving average parameter. Now if $\Theta$ equal to zero so we have a white noise process, if $\Theta$ gets positive values, process is more irregular than white noise, and when the is... | 49,852 |
<p>I am trying to prove/disprove that one time series is leading trend for the other ones. Two time series are (probably) independent and the movements are caused by some (let's assume unknown) common factors. What method would be most appropriate? I also want to find the leading period? Data is quarterly.</p> | 70,651 |
<p>I wish to better understand the pros/cons for using either loess or a smoothing splines for smoothing some curve.</p>
<p>Another variation of my question is if there is a way to construct a smoothing spline in a way that will yield the same results as using loess.</p>
<p>Any reference or insight are welcomed.</p>
... | 31,715 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/20039/effect-of-moving-average-parameter-on-variability-and-variance-of-demand">Effect of moving average parameter on variability and variance of demand</a> </p>
</blockquote>
<p>What is the effect of Thet... | 49,852 |
<p>I have been watching Tom Mitchell's lecture on Bayes Nets: </p>
<p><a href="http://cc-web.isri.cmu.edu/CourseCast/Viewer/Default.aspx?id=bc507778-7a18-4121-b345-" rel="nofollow">http://cc-web.isri.cmu.edu/CourseCast/Viewer/Default.aspx?id=bc507778-7a18-4121-b345-</a>
83d9bab72f55 </p>
<p>He states the following by... | 404 |
<p>I am trying to implement an algorithm for calculating $p$-values of $F$-tests and I need this method to be highly precise. It is easy to implement this with $z$- or $t$- tables, however I don't know how to do this with $F$-values. I have seen some online calculators that do this job, what method do they use? Interpo... | 70,652 |
<p>I have a panel of bond spreads. Spreads are from a specific issuer (firm) and maturity (eg 2, 4, etc years). The problem is that Stata's tsset (or xtreg) command takes two variables to set the data structure. In my case no two variables uniquely identifies each observation.</p>
<p>If I do:
tsset issuer_id Date</p>
... | 42,274 |
<p>I have two 2 hours of GPS data with a sampling rate of 1 Hz (7200 measurements). The data are given in the form $(X, X_\sigma, Y, Y_\sigma, Z, Z_\sigma)$, where $N_\sigma$ is the measurement uncertainty.</p>
<p>When I take the mean of all measurements (e.g. the average Z value of those two hours), what is its stand... | 70,653 |
<p>If one is conducting a survey in which all the respondents are volunteers, would there be a true sampling frame? </p>
<p>I see three possibilities:</p>
<ol>
<li><p>We could view this as a situation where there is no set list of subjects from which those that end up being included in the sample are chosen -- so th... | 70,654 |
<p>How do we specify negative costs in rpart? The documentation says the diagonals of the loss matrix should be zero. Is there an alternative to specify the benefits of correct classification (that is, the negative cost)?</p> | 70,655 |
<p>I wish to analyse the following :</p>
<p>Independent Variable (IV): User of online financial reports Perceived usefulness and Perceived Quality (Sub to Relevance, Reliability, Understandability, Comparability and Timeliness) (all using 5-point Likert scale.) towards Internet Financial Reporting in Malaysia.</p>
<p... | 31,718 |
<p>I have a text classification problem, where there are many different classes, and the text to be classified is very short (about 1 sentence each):</p>
<pre><code>this is sentence one, label1
this is sentence two, label2
...
</code></pre>
<p>I am using the words in the the text as features with a naive bayes classi... | 18,223 |
<p>I have a question about the <code>rugarch</code> package. </p>
<p>My sample size is 43 and I have a problem to model a garch whose mean equation includes an exogenous model; otherwise my mean equation is linear regression, that is, $y_i=a+bx_i+e_i$ that $i=1, \ldots, 43$ and $e_i$ follow a $\text{garch}(1,1)$. But ... | 70,656 |
<p>Suppose that there is a data-generating process
$$
y = \alpha + g(x) + \epsilon
$$</p>
<p>which is to say that an outcome is some function of $x$. Suppose that $x$ is randomly assigned, so $\text{Cov}(x,\epsilon)=0$. But the functional form mappying $x$ to $y$ is unknown. Say that $y$ is continuous and the varia... | 926 |
<p>I am learning about ACF and PACF graphs. I am not sure I understand how to interpret the one I got for my data.</p>
<p>I have searched google for some ACF and PACF examples, and I found some samples of different processes, however, the one I am getting doesn't look similar to any. Does this means there is no season... | 31,720 |
<p>I am trying to determine whether the data depicted in the following figure shows a plateau phase for higher scramblings.</p>
<p><img src="http://i.stack.imgur.com/QaBpZ.png" alt="enter image description here"></p>
<p>As I have often been encouraged to use linear models instead of anova - I have decided to tackle t... | 70,657 |
<p>I have been using the VAR {vars} program to find a fit for the following bi-variate time series (subset):</p>
<pre><code>bivariateTS <- structure(c(0.950415958293559, 0.96077848972081, 0.964348957109053,
0.967852884998915, 0.967773510751625, 0.970342843688257, 0.97613937178359,
0.980118627997436, 0.98705949377... | 70,658 |
<p>If I have a star rating system where users can express their preference for a product or item, how can I detect statistically if the votes are highly "divided". Meaning, even if the average is 3 out of 5, for a given product, how can I detect if that is a 1-5 split versus a consensus 3, using just the data (no gra... | 25,278 |
<p>I am a student at RSM and I have a question regarding my regression analysis for my thesis as I have encountered issues I do not know how to deal with.</p>
<p>I have performance data (dependent variable) of companies in 13 different countries, all of which are the ones I wish to regress against financial liberaliza... | 42,291 |
<p>I am trying to define my own likelihood in rjags. I want to define the CDF of bivariate normal distribution under rjags. Does anyone know how to define the CDf of bivariate normal in rjags?</p> | 42,292 |
<p>I have a huge number, say $M$, of hypotheses that are potentially correlated. I have a dataset $D$ of random samples from an unknown distribution and I want to do test the hypotheses for significance using $D$, while controlling the FamilyWise Error Rate (FWER) to be, say, at most $\delta$.</p>
<p>Some people have ... | 70,659 |
<p>I'm trying to find out how log-likelihood function works for linear regression. I found the formula <a href="http://amath.colorado.edu/courses/7400/2010Spr/lecture4.pdf">here</a> and <a href="http://www.xycoon.com/lsrloglikelihood.htm">here</a>. Making some experiments with it (see code below), I was quite surprised... | 40,715 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/16552/probability-of-mean-of-random-sample-being-in-a-certain-range">Probability of mean of random sample being in a certain range</a> </p>
</blockquote>
<p>When a pizza restaurant’s delivery process is op... | 49,811 |
<p>I want to know what statistics should be used to measure the mixing of languages in cities in a country/state. I have samples from individuals and know the language they speak and the city they live in. The cities are not all the same size and there are 3 different language groups.</p>
<p>The samples are taken unif... | 70,660 |
<p>This is probably really simple but I can't figure it out... was trying for few days...</p>
<p>If <em>all the coefficients of a positive-definite covariance matrix are positive,</em> how can I prove that the coefficients of the first principal component are all of the same sign and the coefficients of all other prin... | 70,661 |
<p>I want to perform a two-sample T-test to test for a difference between two independent samples which each sample abides by the assumptions of the T-test (each distribution can be assumed to be independent and identically distributed as Normal with equal variance). The only complication from the basic two-sample T-te... | 31,727 |
<p>This post is the continuation of another post related to a <a href="http://stats.stackexchange.com/questions/1142/simple-algorithm-for-online-outlier-detection-of-a-generic-time-series">generic method for outlier detection in time series</a>.
Basically, at this point I'm interested in a robust way to discover the pe... | 49,324 |
<p>The question in short: What methods can be used to quantify distributional relationships between data when the distribution is un-known?</p>
<p>Now the longer story: I have a list of distributions and would like to rank them based on their similarity to a given base-line distribution. Correlation jumps into my mind... | 42,302 |
<p>My goal is to make a logistic regression. </p>
<p>The <code>DV</code> is a yes or no variable, and I already found 3 significant <code>IV</code> in my model. </p>
<p>The problem is: I have 5 other categorial (yes or no) variables (they are nearly about the same topic) that I think they have an impact in the <code... | 70,662 |
<p>In SmartPLS, bootstrapping is used to generate the t statistic from which statistical significance can be judged. The two main bootstrapping parameters are case and sample size. Increasing the sample only seems to ensure that the t statistic is stable. Increasing the case size seems to greatly increase the t statist... | 70,663 |
<p>Are the phi and Matthews correlation coefficients the same concept?</p>
<p>How are they related or equivalent to Pearson correlation coefficient for two binary variables? I assume the binary values are $0$ and $1$.</p>
<p>Thanks and regards!</p>
<hr>
<p>The Pearson's correlation between two Bernoulli random vari... | 40,767 |
<p>It is permissible to analyse data for a group of persons, which contains repeated measures data and independent measures data. </p>
<p>Can I analyse this data as if it comes from one group? If not why not? </p>
<p>Thanks for your answers</p> | 70,664 |
<p>When I run a mutiple regression on 3 independent variables(2 dummy variables with multiple levels each and a metric variable).</p>
<p>In my result only few levels of a dummy variable are significant. The result of the levels for the same dummy variable are insignifcant.</p>
<p>How do I interpret it? Is the whole v... | 70,665 |
<p>I am learning linear models, and I do not understand the following:</p>
<p>$\text{Var}(AZ)=A \text{Var}(Z) A^T$ where $A$ is a constant matrix. I want to know the variance $\widehat{\beta}$ in a linear model: $y=A\beta + \epsilon$, and $\widehat{\beta}=(A^T A)^{-1}A^T y$. </p>
<p>To show $\widehat{\beta}=\sigma^... | 70,666 |
<p>So apparently, our subject research proposal was turned down because we used Spearman's correlation to determine if there is any existing relationship between the time spent in playing video games and the grades of 240 students. We were told that Spearman's correlation could only be used at a max of 120 students, wh... | 70,667 |
<p>I was just running some simulations on tossing a coin given certain conditions, to test out some ideas I had. I was trying to find the ratio $\frac{\mathtt{successful\ tosses}}{\mathtt{total\ tosses}}$. Coin tosses were iid.</p>
<p>At first, I was running simulations of 10,000 coin tosses, and I would have the prog... | 6,076 |
<p>I'm implementing decision tree based on CART algorithm and I have a question. Now I can classify data, but my task is not only classify data. I want have a probability of right classification in end nodes.<br>
For example. I have dataset that contains data of classes A and B. When I put an instance of some class to ... | 70,668 |
<p>This is not homework!
I have two very different answers for a power calculation I have done on the below data - </p>
<pre><code>n = 50 in total, 25 in each group
hit = if the number called is then thrown on a dice
probability of hit = 1/6
each person has 36 dice throws
control group = call random number then thro... | 31,739 |
<p>Can you measure the covariance of three or more variables simultanesously? </p> | 70,669 |
<p>I want to use the Levene test to quantify the homo/heterogeneity of the variances of two samples. The density plot looks like this: <img src="http://i.stack.imgur.com/446M5.png" alt="Density plot of samples"></p>
<p>But the Levene test for the data [<code>hov(average~window,data=df)</code>] yields 1.531-e13, i.e. t... | 70,670 |
<p>I'm trying to predict when a location has enough wind to go sailing. I've built several models that look for correlations between different weather conditions and whether it ends up being windy X hours later. Ultimately, I want to produce something like "Based on current conditions, there is a 70% chance it will be ... | 70,671 |
<p>I need to do a two-sample Kolmogorov-Smirnov (KS) test in <code>R</code>, only I don't understand the formulae and how it works when I look it up. I suspect this is because I don't understand the maths of what goes on in this test and just know whether it will tell me if the data are normally distributed or not. </p... | 70,672 |
<p>I have three different linear, multi-variate time series models with a best fit against the same observed value $Y$ at 1 minute, 3 minutes and 10 minutes horizons respectively. Each model is using different predictors data. There is no serial correlation or ARIMA involved here.</p>
<p>I want to blend the three mode... | 70,673 |
<p>The coefficient of an explanatory variable in a multiple regression tells us the relationship of that explanatory variable with the dependent variable. All this, while 'controlling' for the other explanatory variables.</p>
<p>How I have viewed it so far:</p>
<p>While each coefficient is being calculated, the other... | 70,674 |
<p>What statistical treatment should I used to test my hypothesis (there is no significant relationship or interaction between the 2 variables with respect to their preferences) if I have three samples and my data are expressed in frequency?</p> | 70,675 |
<p>To test whether you want to add an interaction term to your model, is an interaction plot only useful when both effects are fixed. How do you determine whether to add interactions between random factors and fixed factors?</p> | 70,676 |
<p>I am looking for a script that will enable me to download a set of abstracts (or article meta-data of an article) from PubMed by supplying it with a list of PubMed ID (PMID) numbers (e.g., from a .csv file). The ideal script would be for R and then Python, but I am certainly open to any solutions or suggestions. P... | 31,746 |
<p>Suppose you have data in the following format:</p>
<pre><code> <60 60-69 70-79 80-89 90-99
No Exercise 5 10 2 4 1
Moderate 2 4 12 4 3
Heavy 4 5 18 10 2
Extreme 5 6 7 9 12
</code></pre>
<p>The cells represent the numbe... | 31,747 |
<p>I have the following problem:</p>
<p>I have one manipulated IV (degree of co-creation) based on three surveys "no" "low" and "high" degrees of co-creation.
Furthermore I have 4 DV (Purchase intention, loyalty, word of mouth, willingness to pay)
I want to test whether the degree of co-creation has a direct effect o... | 31,748 |
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