question stringlengths 37 38.8k | group_id int64 0 74.5k |
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<p>For a statistics class, I have to prove a result which leads me to the following question. If I can show that it is true, my proof is done. So here is the question.</p>
<p>Suppose that $U: \Omega \rightarrow [0,1]$ is a random variable uniformly distributed on $[0, 1]$ and $X: \Omega \rightarrow \mathbb{R}$ is cont... | 34,309 |
<p>I want to predict the outcome of a particular treatment (remitted or not) using demographic, plasma biomarker, genetic, and clinical data. IS a neural network model the best way of doing this? What advantages does this have over traditional logistic regression model building? How limited am I with only 120 cases and... | 72,399 |
<p>I am new in using RF. I want to use it to compute the relative importance of the features. I found the weight is very small ("party" package, cforest). Is there anyway to get these weights in a range of 0-1? The total weight would sum up to 1? For example, if $x_1$, $x_2$ and $x_3$ are the features, the relative imp... | 34,312 |
<p>I have a data set of teams. Each team has a sum of points. I want to divide the teams in ranges of points (0 - 999; 1000 - 1999; etc) such as that the top range (with the most points) is smaller (has less teams) than the next and so on. Suppose the number of ranges is 7 and the angle is X degrees like in this figure... | 18,518 |
<p>I have a forecasting model for a time series and I want to calculate its out-of-sample prediction error. At the moment the strategy I'm following is the one suggested on <a href="http://robjhyndman.com/researchtips/crossvalidation/">Rob Hyndman's blog</a> (near the bottom of the page) which goes like this (assuming ... | 34,313 |
<p>I know the formula for the likelihood of some parameters given the data. The result has to be maximised and I can avoid multiplication using the log. How can I make this a minimisation problem (i.e. rewrite the given formula). I presume it is not as easy as taking the negative log and than adding things - or is it? ... | 72,400 |
<p><strong>Prologue</strong></p>
<p>I have a matrix $N$ with dimensions $I\times J$, $I >> J$, and $n_{ij}$ is assumed to follow a Poisson distribution with mean $\lambda_{ij}$. Using a method (say <em>NtoM</em>), I reduce $N$ to a matrix $M$ with dimensions $I \times K$ (rows correspond to that of $N$, however ... | 72,401 |
<p>I have 4 sample pairs, let's say (x1, y1),...,(x4, y4). </p>
<ul>
<li>What is the minimum sample size for a paired t-test?</li>
<li>Which assumption should I check for paired t-test? </li>
<li>If my data is non-normal, what is an alternative non-parametric test?</li>
</ul> | 87 |
<p>I have data for the population of a number of different fish, sampled over a period of about 5 years, but in a very irregular pattern. Sometimes there are months between samples, sometimes there are several samples in one month. There are also many 0 counts</p>
<p>How to deal with such data? </p>
<p>I can graph i... | 34,318 |
<p>I'm looking for a R package to compute sample size for the differences of two proportions via confidence inetrval (CI). Note that there are several methods to compute CI for the difference in proportions, and for some of these methods one can compute sample size with pencil and paper, but I was wondering if there is... | 45,424 |
<p>Say you have $n$ different, non-normal, potentially overlapping data sets of samples. Maybe their densities look something like:</p>
<p><img src="http://i.stack.imgur.com/OjZ6q.png"></p>
<p>and you are given a new sample $x$, how would you decide to which of these sample sets it would most likely belong?</p>
<p>I... | 49,895 |
<p>I am looking for existing implementations for co-clustering (aka biclustering). I came up with <code>biclust</code> function available in MATLAB, but still I am wondering if there are more implementations for this subject, either in MATLAB or R.</p> | 24,037 |
<p>I asked this question on StackOverflow and someone pointed for me to ask this here. </p>
<p>Lets assume that I have 3 variables: x, y, z which are integers.</p>
<p>I have 5000 values of each and I want to predict the 5001th (or other) value given this data set. The thing is, the values oscillate a lot so I was thi... | 72,402 |
<p>I want to fit a model without a correlation term between the random effects with <code>lme</code>. In <code>lmer</code> this is fairly straighforward....</p>
<pre><code># lmer without correlation term
m1 <- lmer(distance ~ (1|Subject) + age + (0+age|Subject) + Sex, data = Orthodont)
VarCorr(m1)
# Groups Name ... | 72,403 |
<p>For a simulation study, I contrast the power of different LMEMs for repeated measures. To get p-values, I use likelihood ratio tests where I compare a model including a fixed treatment effect with one that has the same random effects structure but without having the fixed treatment effect. I want to specify a model ... | 11,093 |
<p>From what I understand, <a href="http://en.wikipedia.org/wiki/Jackknife_%28statistics%29" rel="nofollow">jackknife</a> and <a href="http://en.wikipedia.org/wiki/Bootstrapping_%28statistics%29" rel="nofollow">bootstrapping</a> are frequentist methods for computing statistics (bias, variance, etc.) of an estimator.</p... | 72,404 |
<p>What is the most "natural" family of distributions on an interval [0,1] indexed by their mean $\mu$ and standard deviation $\sigma$? I am looking for something occurring in "nature", like normal distributions, except that it has to take values from 0 to 1. </p> | 72,405 |
<p>My regression results are as follows. </p>
<pre><code>Variable B exp(B)
age 0.004575 1.004586
capital 0.2250 1.2524
year -0.1026 0.9024
</code></pre>
<p>Can someone please help me to interpret these?
(eg: one year increase in age would increase/decrease the hazard by Xx%)</... | 72,406 |
<p>I'm a psycholinguistics student with few knowledge in statistics and I have some doubts about a Correlation of Fixed Effects in lmer function (lme4 package). So, if my question is stupid… hummm… I'm sorry!</p>
<p>My response variable is RT (Reaction Time in a self-paced reading experiment) and my independent variab... | 72,407 |
<p>I'm trying to forecast customer orders, and want to incorporate real-time forecast errors into my forecast. </p>
<p>Say it's Monday, and I forecast that the customer will order 100 units on Wednesday. To make things as easy as possible, suppose that he'll just make one order this week.</p>
<p>There are a lot of ... | 72,408 |
<p>In my text book is says:</p>
<blockquote>
<p>Regress each of $y_t, x_{t1}$, and $x_{t2}$ on a constant and the time trend $t$ and save the residuals...</p>
</blockquote>
<p>What do they mean regress each on a constant? What constant specifically? This is coming from a section in the textbook (introductory econom... | 72,409 |
<p>I want to test how well my data fits a uniform distribution and use this as one factor in a likelihood function I am constructing.</p>
<p>Unfortunately, I have no solid basis in statistics. So far, I figured out that a good criterion to use is the Kolmogorov-Smirnov test. I can do the test, but I do not know what t... | 34,323 |
<p>So like the title states, do the time periods in time series data have to be of equal intervals? For example, if we wanted to have data on the level of education recorded by year, would we need observations for 1996, 1997, 1998,...,2002 or could we have data for 1996, 2000, and 2004? It seems to me that it would nee... | 34,324 |
<p>I am working on a time series analysis with 52 quarterly data concerning a variety of possible determinants of CO$_2$ emissions by transport (CO$_2$ taxes, GDP, load factor, transport volume). This means I will have at least 3 independent variables.</p>
<p>I am using Stata and I want to see if there is a long and s... | 72,410 |
<p>I have run a multiple regression to determine which factors predict the willingness to pay for members of another group.</p>
<p>The multiple regression determined that symbolic threat (fear of a cultural and traditional attack on group values by others) was the only significant predictor of how much one would pay f... | 72,411 |
<p>I conducted purposeful selection as outlined in Jewell's <em>Statistics for Epidemiology</em>. The log likelihood tests showed covariates, which I considered to be confounding though not significant in the modeling, as not significant when excluded. In the end, however, goodness of fit test was significant. When re-... | 854 |
<p>In a BIBD, let</p>
<p>$a$ denote the number of treatments;</p>
<p>$b$ denote the number of blocks;</p>
<p>$k$ denote the number of treatments exactly in each block;</p>
<p>$\lambda$ is the number of times each pair of treatments appears in the same block.</p>
<p>Each treatment occurs $r$ times.</p>
<p>How are ... | 72,412 |
<p>I'm using a very simple data set from an article in trying to further my understanding of GLMs. I've input the data using SAS, and I've run both the PROC REG and PROC GENMOD procedures on the data. In the PROC GENMOD procedure, I used a log link with a normal distribution; in the PROC REG procedure, I used the log... | 72,413 |
<p>I conducted an experiment with 21 subjects. Each subjects performed 80 trials for 3 different categories of test (total 240 trials). What I need to do now is look for a correlation between category 1/2/3 for each of the 80 trials and I need to do that by collapsing all subjects data as if they were produced by one s... | 72,414 |
<p>I have a graphical model with binary variables Y, X1, X2, and observed data D.</p>
<p>D depends on Y
X1 and X2 depend on Y</p>
<p>When Y is false, X1 and X2 are independent:</p>
<pre><code>(D) <-- (Y) --> (X1)
|
V
(X2)
</code></pre>
<p>However, when Y is true, X1 and X2 are not in... | 72,415 |
<p>I am constructing a model for the prediction of a binary (Yes/No) outcome. I have a learning sample that gives the machine 1500 examples of the "Yes" group and 500 example of the "No" group. Should I be using all the data I have for input to learn the machine? Would this be biased towards the "Yes"? </p>
<p>I had t... | 72,416 |
<p>In one of my questions:</p>
<p><a href="http://stats.stackexchange.com/questions/79641/how-to-measure-test-set-error-with-logistic-regression">How to measure test set error with logistic regression</a></p>
<p>One of the answers mentioned "concordance probability" or c-index. Unfortunately I'm not familiar with the... | 49,896 |
<p>I see that lots of machine learning algorithms work better with mean cancellation and covariance equalization. For example, Neural Networks tend to converge faster, and K-Means generally gives better clustering with pre-processed features. I do not see the intuition behind these pre-processing steps lead to improved... | 49,476 |
<p>There are two laboratories measuring identical samples. One of the lab's data is non-normal, therefore I am looking for a non-parametric test.</p>
<p>After comparing overall differences in the dependent variable (continuous) using Wilcoxon Mann-Whitney, I wish to test for differences between labs based on a third v... | 34,342 |
<p>I'm having a hard to deciding which of a two-sample t-test and a chi-squared test is more appropriate for these sorts of questions. Examples would be:</p>
<p>70 out of 120 americans like hotdogs. 50 out of 95 europeans like hotdogs. Do the two groups differ in their hotdog opinions?</p>
<p>1000 each of caucasians,... | 45,439 |
<p>I am trying to determine why I am getting different results with these different Wilcoxson test implementations in R version 2.15.2. I have paired data with some ties. I have read the response for <a href="http://stats.stackexchange.com/questions/31417/what-is-the-difference-between-wilcox-test-and-wilcox-test-in-r"... | 34,344 |
<p>I'm new to decision trees and I have some confusion about how factor variables and non-ordered character/string variables get handled in a split.</p>
<p>Suppose I have a factor such as "tiny, small, medium, large, huge" where the levels are important. How does a decision tree try to find the best split? Will it onl... | 72,417 |
<p>I am trying to apply dimensionality reduction on an a set of images (~3000 pixels) using Matlab's Dimensionality Reduction toolbox. However, I know very little about dimension reduction. So I tried several functions by trial and error. PCA returned a matrix with complex numbers, and the others froze MATLAB. Can I ge... | 30,819 |
<p>I know this is the <a href="http://heapol.oxfordjournals.org/content/early/2011/01/27/heapol.czr004.full.pdf+html" rel="nofollow">general specification</a> for a single group:</p>
<p>$Y_i$ = $\beta_0$ + $\beta_1$*time + $\beta_2$*post + $\beta_3$*timepost</p>
<p>where <code>time</code> is a continuous variable ind... | 72,418 |
<p>I have a learned Hidden Markov Model (HMM) from a certain sequential data using Gibbs sampling. I have managed to obtain the transition probabilities (transition matrix) of the Markov chain and the params of the probability distributions of the hidden states. The only set of params that I have yet been able to obtai... | 72,419 |
<p>I wish to estimate the state of a system from two separate and disparate observations. A simple approach that I have seen in some literature is to combine the feature vectors (observations) by simply concatenating them. So if the first observation is denoted $x \in \Re^{10}$ and the second is denoted $y \in \Re^5$, ... | 163 |
<p>We have x1 and x2 representing variations in temperature and pressure and the response is yield of penicillin. What is the practical reason for using the points (-1,-1), (-1,1), (1,-1), (1,1) rather than using (0,0) in place (-1,-1)?
Is it because using (0,0) would force it through the origin?</p>
<p>Also, is repli... | 9,624 |
<p>In the AR(1) model $y_{t}=\beta_{0}+\beta_{1}y_{t-1}+u_{t}$, assuming $E(u_{t-1}|y_{t-1},y_{t-2}...)=0$, how does the law of iterated expectations ensure that the errors must be uncorrelated: $E(u_{t}u_{s}|x_{t},x_{s})=0$?</p> | 72,420 |
<p>We have a data-point x and many classes. Let $P(c|x)$ the probability that $x$ is of class $c$. We note $c_1$ the most probable class for $x$ (i.e. $P_1=P(c_1|x)$ is the highest probability), $c_2$ the second most probable class for $x$ (i.e. $P_2=P(c_2|x)$ is the second highest probability ($P_1> P_2$)).</p>
<p... | 34,351 |
<p>How to estimate the out crosses rate in crops?
in have experiment included; main plot (1- seeds from open field 2- seeds from free pollinators cage 3-seeds from pollinator cage), sub plot (5 genotypes) and 50 plants grown for each genotype in each plot. This in three replications. It easy to estimate variance betwe... | 72,421 |
<p>I've come across a scenario where I have 10 signals/person for 10 people (so 100 samples) containing 14000 data points (dimensions) that I need to pass to a classifier. I would like to reduce the dimensionality of this data and PCA seems to be the way to do so. However, I've only been able to find examples of PCA wh... | 72,422 |
<p>I recently ran an experiment assessing the impact of three system factors (factor A; factor B; factor C) on user attitudes (4-item scale). Each system factor had two levels (high vs. low). As a result, my experiment had nine conditions: eight treatment conditions (reflecting the 2x2x2 design) plus one control group.... | 72,423 |
<p>I'm an enthusiastic single developer working on a small start-up idea. I reduced a corpus of mine to an LSA/LDA vector space using <code>gensim</code>. Now I have a bunch of topics hanging around and I am not sure how to cluster the corpus documents. I see that some people use k-means to cluster the topics. Can some... | 72,424 |
<p>I'm relatively new to statistics, and understand that my question may be completely misworded. I am testing my own algorithm versus another. While the outputs are not identical, I want to show that the differences are "statistically insignificant." How can I quantify this, to make my point?</p> | 48,699 |
<p>Can someone show me why for a distribution function $F$ on $(0,\infty)$, $0 < y \leq x$, the following holds: </p>
<p>$\frac{F(x)-F^{*2}(x)}{\overline{F}(x)}=\int\limits_{0}^{x}\frac{\overline{F}(x-t)}{\overline{F}(x)}dF(t)$</p>
<p>Edit: $F^{*2}$ stands for the convolution of $F$ with itself:</p>
<p>$F^{*2}= F... | 72,425 |
<p>Please let me know how to perform recursive clustering in R? How to give the input of the 1st iteration of cluster to the next one and so on. Any tutorial in this would be of great help.</p> | 45,457 |
<p>While studying logistic modeling, I read the following statement</p>
<blockquote>
<p>The fact that only odds ratios, not individual risks, can be estimated from logistic<br>
modeling in case-control or cross-sectional studies is not surprising.</p>
</blockquote>
<p>I do not know what do the "case-control" an... | 72,426 |
<p>I'm teaching an intro stats class and was reviewing the types of sampling, including systematic sampling where you sample every kth individual or object. </p>
<p>A student asked if sampling every person with a particular characteristic would accomplish the same thing. </p>
<p>For example, would sampling every pers... | 45,459 |
<p>I am performing multiple regression analyses and I am not sure whether outliers in my data should be deleted. The data I am concerned about appear as "circles" on the SPSS boxplots, however there are no asterisks (which makes me think they are not 'that bad'). The cases I am concerned about do appear under the "case... | 34,358 |
<p>I would like to use <strong>ksvm</strong> from the <strong>kernlab</strong> package in <strong>R</strong> to train and test a support vector machine. I'm able to use it but I would like to use different values of <em>C</em> for each observations. To be more precise, I want to solve the following minimization problem... | 18,778 |
<p>The dependent variables (DV) have to be normally distributed. I have a problem because some of them aren't. I have one independent variable (IV), namely <em>type of education</em>. The DV's are <em>Externalizing problems</em>, <em>Internalizing problems</em>, <em>Self-image</em>, <em>Motivation</em>, <em>Neuroticism... | 72,427 |
<p>The <a href="http://www.graphpad.com/faq/viewfaq.cfm?faq=1099" rel="nofollow">help page</a> for Prism gives the following explanation for how it computes the prediction bands for non-linear regression. Please excuse the long quote, but I am not following the second paragraph (that explains how $G|x$ is defined and ... | 72,428 |
<p>The response variable in my ordered logit model has 5 categories ranging from '1 = strongly disagree' to '5 = strongly agree'. However, only 0.3% of observations fall into category 1 (4 observations out of 1,320). This has created some problems, such as the inability to test the assumption of parallel lines (Brant t... | 72,429 |
<p>A person is given 10 sample images (based on the same image) with corresponding techniques on how the image was achieved. I want to regress the matrix bitmap of the image of the 10 images on the image created by the person as a gross way of knowing which images the person copied from. I am assuming that if the perso... | 6,529 |
<p>In the research, both autocorrelation and heteroskedasticity are detected in panel data analysis. I can solve them separately in stata with command "xtregar" and "robust", respectly. However, I cannot find a way to solve both problems at the same time.<br>
If possible, please show me how to repair autocorrelation an... | 34,365 |
<p>When working with many input variables, we are often concerned about <a href="http://en.wikipedia.org/wiki/Multicollinearity">multicollinearity</a>. There are a number of measures of multicollinearity that are used to detect, think about, and / or communicate multicollinearity. Some common recommendations are: </... | 72,430 |
<p>There is an example on the computation of Gower's similarity coefficient on the page,</p>
<p><a href="http://www.clustan.com/gower_example.html" rel="nofollow">Gower's similarity coefficient</a></p>
<p>I am trying to work out the similarity manually between patient 1 and 2, however my computation is giving me comp... | 48,747 |
<p>In <em>Davidson & McKinnon - Estimation and Inference</em> I read that in a competitive market which is always in equilibrium we observe:</p>
<p>$Q^d_t = Q^s_t = Q_t$</p>
<p>where $Q^d_t$ is the quantitiy of demand, $Q^s_t$ the quantitiy supplied.</p>
<p>If one would estimate the equation (1) by OLS in a mode... | 72,431 |
<p>I have a large data set that I would like to cluster using spherical K means algorithm. However, I am relatively new to this subject and R in general. Most of my knowledge is self taught and I am still in the beginning stages- I have read all about K means clustering in the past few days and I would like to apply it... | 72,432 |
<p>I have an unbalanced panel data set with more than 400,000 observations over 20 years. My panel variable is a person id and my time series variable is the year. The persons are from all over Germany which means that they are from different regions. To account for possible correlations between the persons within the ... | 72,433 |
<p>For reasons owing to mathematical convenience, when finding MLEs (maximum likelihood estimates), it is often the log-likelihood function---as opposed to the standard likelihood function---which is maximised.</p>
<p>From what I've gathered, this approach is deemed valid as a result of the monotonically increasing na... | 42,718 |
<p>In this exercise, I was asked to prove that the simple linear regression - ( $Y_i=\beta_0+\beta_1X_i+\epsilon_i$ with all the usual basic conditions) - of $\{Y_{ji}\}$ for each $X_i$ is the same as the linear regression of ${\bar{Y}_i}$ for each $X_i$, where $\bar{Y}_i=\sum_j^nY_{ji}$ . This I managed to prove.</p>... | 34,370 |
<p>Suppose $y$ is a continuous random variable and $d$ is a binary random variable that takes the value $1$ with probability $p$ and $0$ with probability $1-p$. </p>
<p>How do I show that $\text{Cov}(y,d)=(E[y|d=1]-E[y|d=0])p(1-p)$?</p> | 72,434 |
<p>Sorry if the title is a bit vague however, i'm not sure exactly how to make my sentence concise.
I have two times series:
Amount invested into Iraq across time (in months)
Price of a stock across time (averaged each month)</p>
<p>There area few things i want to find out however, i'm only at an intro level stats a... | 72,435 |
<p>We are learning pivot functions, test statistics, and hypothesis testing at university but it makes no sense. I've tried reading my text book/notes, going through examples, etc., but the concepts seem like a random guess and I'm clueless about how to even start guessing what the answer could be. </p>
<h3>1st part</... | 72,436 |
<p>I am using WinBUGS to estimate / update the parameters of a model. The model is:
$$
\begin{aligned}
D(T,B,a)&= B*(a_0+a_1T+a_2T^2+a_3T^3)+error(B,T,a) \\
error &= \mathcal N(0, B^{0.5}a_4(a_0+a_1T+a_2T^2+a_3T^3))
\end{aligned}
$$
where $D$ is an observed response, $B$ and $T$ are observed input parameters... | 44,793 |
<p>I am trying to work out how good my particular model is at explaining some observed data. The problem here is that the observed data takes the form of averaged (mean) values for each of my predictive scores. When performing a simple correlation, I get a really high R-squared value (and this is repeated for indepen... | 44,844 |
<p>I asked <a href="http://stackoverflow.com/questions/5130808/how-to-correlate-two-time-series-with-gaps-and-different-time-bases"><strong>this question</strong></a> over on StackOverflow, and was recommended to ask it here. </p>
<hr>
<p>I have two time series of 3D accelerometer data that have different time bases ... | 34,375 |
<p>I have a set <strong>H</strong> of <code>k</code> <code>m</code>-dimensional hyperplanes in <code>n</code> dimensional space, where <code>1<<m<<n<<k</code>. I want to find an <code>m</code>-dimensional hyperplane <strong>p</strong> that's closest to <strong>H</strong>. However, a significant portio... | 6,532 |
<p>I have an SVM classifier for m classes and n data points (somewhat evenly distributed across each class). Could I use the resulting MxN log likelihood matrix to merge classes that are similar? </p> | 72,437 |
<p>I am trying to understand when MCMC algorithms are utilized. I can do density estimation with MLE for non-linear cases just like linear cases, and EM for hidden variables and missing values. What are the scenarios when these tools are not sufficient and we use MCMC?</p>
<p>Thanks</p> | 72,438 |
<p>I am currently learning to use support vector machine as classification. I have a data set with 161 observation and 18 dimension. I get 160 support vectors using svm function form R package, e1071. The obtained accuracy is 1. Can someone tell whether the result is accurate or not?
actually I've found svm example fr... | 72,439 |
<p>In a regression tree, it is often assumed that each leaf is a Gaussian distribution $\mathcal{N}(\mu_i, \sigma)$, where $i$ is the index the leaf. Is $\sigma$ calculated as the standard deviation <em>within a leaf</em> or the standard deviation for the dataset? </p>
<p>If a tree is grown such that each leaf contain... | 72,440 |
<p>I have a situation where there are n individuals and p features (variables). I do have their cluster information. Here is an example:</p>
<pre><code>myd <- data.frame (
sub1 = c(1, "AB", "AB", "BB", "BB", "AA", "BB", "AB", "AA", "BB", "AB", "AA", "AB"),
sub2 = c(1, "AB", "BB", "BB", "BB", "AA", "BB", "AB", "AA"... | 34,379 |
<p>How can I calculate the robust standard error of the predicted <em>y</em> from a linear regression model in R? Any suggestion is appreciated.</p> | 72,441 |
<p>I have a relatively small sample of binary events (50-100 events) that occurred during a time of day (the success rate is closely related to the time of day). </p>
<p>I'm grouping these events into hour intervals, for example:</p>
<ul>
<li>..</li>
<li>[08:00-09:00) success: 5; failure: 7; 42% success</li>
<li>[09:... | 72,442 |
<p>I have the following SAS code that uses <a href="http://support.sas.com/documentation/cdl/en/etsug/60372/HTML/default/viewer.htm#etsug_forecast_sect016.htm" rel="nofollow">PROC FORECAST</a> that I would like to replicated with the Python Pandas <a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.st... | 72,443 |
<p>I have a large csv file with around 45,000 rows and about 6 columns.</p>
<p>The columns are set-up like:</p>
<pre><code>Module, File-path, Status, Version-Old, Version-New, Change-diff
</code></pre>
<p><em>Change-diff</em> is simply the result of doing: <em>New - Old</em>.</p>
<p>There are around 30 different mo... | 45,504 |
<p>In a lattice xyplot with multiple smooth curves, I plotted curves categorized by color (y1, y2, y3 in blue; z1, z2, z3 in red).</p>
<p>If we consider the following simple data :</p>
<pre><code>x<-1:50
y1<-rnorm(50,100,20)
y2<-rnorm(50,80,20)
y3<-rnorm(50,90,20)
z1<-rnorm(50,60,20)
z2<-rnorm(50,40... | 45,505 |
<p>In what circumstances would you want to, or not want to scale or standardize a variable prior to model fitting? And what are the advantages / disadvantages of scaling a variable?</p> | 49,625 |
<p>Given two samples of arrival rate of a process (they should end up something like a Poisson distribution):</p>
<ul>
<li>One over a long period (something like several days)</li>
<li>Another from a shorter period time (maybe 30 minutes)</li>
</ul>
<p>How can I compare the shorter distribution to see if it varies si... | 34,381 |
<p>Spuriously high R-squared is one of the pitfalls of regression through the origin (i.e. zero-intercept models). If the predictors do not contain zeroes, then is it an extrapolation? What are the uses and other pitfalls of regression through the origin? Are there any peer-reviewed articles?</p> | 72,444 |
<p>I am trying to implement the K-mean analysis with the <a href="http://en.wikipedia.org/wiki/K-means_clustering" rel="nofollow">Standard algorithm</a>.</p>
<p>My implementation seems to work, but I noticed some strange behavior. If the <em>k</em> is close to half of the length of the list to be analyzed, I will get ... | 34,387 |
<p>I have a small black box that displays a 0 or a 1 every time I press its button. </p>
<p>I can tell you, truthfully, that over the past 20,000,000,000 times it has been pressed, 19,999,999,990 times it has shown a 1.</p>
<p>I ask you to make a prediction of what number will appear when I press the button next.</p>... | 19,028 |
<p>Suppose $N$ experiments can be made in varying conditions. Each of them yields an estimate $f_i$ of a continuous (and, if necessary, positive) function of x over some interval. Experiment $i$ is repeated a number of times $n_i$, and each time it yields a function $f_i^j$. I am given the following data
$$\forall x \q... | 72,445 |
<p>I have three time-series $m_i$, $k_i$, $s_i$, for $i \in [1,N]$.</p>
<p>The problem is to find constants $A_m$, $A_k$, $A_s$,
such that
for $p_i = ( A_m \cdot m_i ) + ( A_k \cdot k_i ) + ( A_s \cdot s_i )$ ,
and a given integer constant $t$</p>
<p> \[ \sum_{i=1}^{N-t} { (m_i - p_i) (p_{t+i} - p_i) } = 0 \]</p>... | 49,043 |
<p>I'm confused by the description of the intraclass correlation (ICC) for a linear mixed model with longitudinal data from this <a href="http://psych.unl.edu/psycrs/944/944_Lecture03_Within-Person.pdf" rel="nofollow">material</a>. A screen capture is shown below.</p>
<p>What I'm confused about is that the ICC describ... | 72,446 |
<p>I'm using SPSS to try and find a mixed model that adequate explains the data that I have.
Two of the explanatory variables are closely related ('Sample group' and 'individual'), as an individual is only
ever part of one sample group, so I've been nesting them if they are in the same model.</p>
<p>I've been using ... | 72,447 |
<p>Is there a way/method/approach to decompose a time series data using regression splines:</p>
<ol>
<li>Seasonal time series into trend+seasonal+random component ?</li>
<li>A non seasonal time series into trend+random component ?</li>
</ol>
<p>I'm familiar with STL, Census and classical decomposition in R. All these... | 72,448 |
<p>Are there graphing techniques (certain kinds of plots) that are similar to the Edward Tufte's box plots - shown below - but that consider the distribution of the data points?</p>
<p><img src="http://i.stack.imgur.com/ZC2SJ.jpg" alt="Edward Tufte style box plots"></p>
<p>But instead of a black line traveling vertic... | 49,897 |
<p>I have a typical problem with several variables and a large amount of data which are not important right now.</p>
<p>The goal of the study is to relate variable $Y$ with variables $X_1,X_2,...,X_n$. I have performed an ANOVA so that I see which variables are able to explain the variability on $Y$. However, my que... | 72,449 |
<p>I don't understand why predictions from <code>lm.ridge()</code> are so far out, when using the "best" lambda, based upon GCV. Can anyone help me to obtain better predictions? Or, at least, does anyone have a good ridge example with a simple explanation of the results?</p>
<p>Below is my R code for wine quality data... | 72,450 |
<p>I've read several articles and excerpts from books that explain how to choose a <em>good</em> number of intervals (bins) for histogram of a data set, but I'm wondering if there's a hard <em>maximum</em> number of intervals based on the number of points in a data set, or some other criterion.</p>
<p><strong>Backgrou... | 72,451 |
<p>I'm currently writing a thesis and I have to interpret a coefficient estimate that's extremely negative compared to what I hypothesized.</p>
<p>How do I best communicate this? Describing it as <code>"very negative"</code> sounds a bit strange, but I can't think of anything better.</p> | 37,645 |
<p>I am pretty new in machine learning and hence facing a lot of confusion in data normalisation concepts. Someone pls clarify the following doubts :</p>
<p>1) While normalising a data matrix of m-samples x n-features, the normalisation should be done along m-samples or along the n-features i.e we normalise each row o... | 72,452 |
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