question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I am new to machine learning, so forgive me if i am doing something absolutely absurd.</p>
<p>I have a classification task (~100 classes) and have about 2 million training data points in a 2000 dimensional space. Coordinates of data points are integers (discrete). All points have non-zero coordinates only for < ... | 1,906 |
<p>The alligators <a href="http://www.openbugs.net/Examples/Aligators.html" rel="nofollow">example</a> from openbugs examples repository is the same example that comes with winbugs.
Basically this is a multinomial logistic regression example in which the outcome variable has 5 possible values and there are two categor... | 18,554 |
<p>To my understanding, Cramer's V cannot be negative because of the way we define it. But here's what I got from SAS:</p>
<p><img src="http://i.stack.imgur.com/smfn6.jpg" alt="enter image description here"></p> | 33,409 |
<p>With given data, I need a line of slope 1 with minimized SSE. Anyone know how I could do this in R or Excel or another program? If you could tell me how to do it mathematically that might help.
Thanks.</p> | 71,761 |
<p>I'm trying to do this project that creates a sort of "universal score" across a set of games - if I play a game that gives me a certain score, and I have a friend who plays a different game and has a certain score in that game, how can I tell whether I am higher or lower ranked than him without playing his game?</p>... | 71,762 |
<p>I'm running a multiple linear regression on a set of sports data. When I run the regression on one season, which has 380 data points and which I thought was a fair amount, I get quite a high p-value on one of my independent variables. However, when I run the regression on all my data points (I have more than 3000 da... | 71,763 |
<p>I ran ind. t-test and find that no significant different for the two means. So, does this meant discouraging? Mean for A is higher than B, so i did planned to conclude that A is actually favoring compared to B. However, in my current state with no significant different btw the two means, what can i conclude from the... | 71,764 |
<p>I am currently working with a presence-absence database that is mostly zeros (~5% are ones) representing species in space (a species per site matrix). I would like to explore the spatial pattern of the species and see whether there is any "natural" grouping of the data that could be thought of as bioregions. I have ... | 33,413 |
<p>I know that linear regression is based on the assumption that the errors are normally distributed (from both bayesian and classical views). I'm just trying to verify this assumption based on the final model.</p>
<p>Assume I've got 3 normal random variables x1, x2, x3. I can regress (linearly) x1 on x2, x3 and get a... | 41,922 |
<p>Can there be a situation where odds ratio is less than lower limit of 95% confidence interval? If yes then what could be the possible reason for this? The formula I used to calculate confidence interval is exp(log(OR)+/-(1.96*SE)).</p> | 71,765 |
<p>I know that this question is not well defined, but some clusters tend to be elliptical or lie in lower dimensional space whilst the other have nonlinear shapes (in 2D or 3D examples).</p>
<p>Is there any measure of nonlinearity (or "shape") of clusters?</p>
<p>Note that in 2D and 3D space, it is not a problem to s... | 71,766 |
<p>I've got 10 (yes, only 10) cases over 1000 variables (e.g. measurements of concentrations of 1000 different compounds at 10 different time points).
I can group these cases into 3 clusters in 1000-dimensional space (complete linkage, cluster sizes 3, 3, and 4). This partitioning agrees with my expectations, but the c... | 33,417 |
<p>I want to find the similarity between a document with documents coded as TF-IDF in a pickle file (Python). TF-IDF is done as offline so there is no problem, but when I send a new document for similarity check it takes around 2 minute while I need something real-time (< 2 seconds). For this purpose I used the foll... | 71,767 |
<p>I am comparing two groups (A and B).</p>
<p>Group B is matched to group A on variable X, by sampling two subjects from a population for each subject in group A. </p>
<p>Group A has ~200 subjects, group B has ~400 subjects. </p>
<p>X is a continues variable that is normally distributed. Because of the matching, X ... | 33,418 |
<p>I recently learned about the median polish method as a robust alternative to ANOVA for the purposes of fitting models to data. But, is there a way to test hypotheses using median polish, such as a particular row median is equal to zero, or one column median is greater than another column median?</p>
<p>Thanks.</p> | 44,380 |
<p>I know there won't be a clear answer to that question but I'm really curious to know your opinion on that matter. I deal with reaction times, and finding a good measure of central tendency is difficult due to the ex-gaussian shape and the outliers. Beyond the mean and median, I discovered recently the trimmed mean a... | 33,420 |
<p>My data takes the form of a stream of events for each customer in my sample. For a given customer, the stream takes the form of a list of events over time: </p>
<blockquote>
<ul>
<li>At T1, customer C1 bought 1 unit of product X</li>
<li>At T2, customer C2 bought 1 unit of product X</li>
<li>At T3, customer... | 71,768 |
<p>I am not a statistician and hope someone can point me towards the right direction. I have some time series data grouped into three classes like this:</p>
<pre><code>Time Period 1 Time Period 2 Time Period 3
-------------------------------------------------
[1,2,3,4,5,6...] [12,13,14,15] [17,3,1,3,4... | 71,769 |
<p>Two random variables are defined as <a href="http://en.wikipedia.org/wiki/Subindependence" rel="nofollow">subindependent</a> if their covariance is zero--in other words, if they are <a href="http://en.wikipedia.org/wiki/Uncorrelated" rel="nofollow">uncorrelated</a>. The latter link notes that "not all uncorrelated v... | 71,770 |
<p>I just read: <a href="http://www.r-statistics.com/2010/02/post-hoc-analysis-for-friedmans-test-r-code/" rel="nofollow">http://www.r-statistics.com/2010/02/post-hoc-analysis-for-friedmans-test-r-code/</a></p>
<p>Here is the example from the blog post:</p>
<blockquote>
<p>Let’s make up a little story: let’s say we... | 71,771 |
<p>If I use <a href="http://en.wikipedia.org/wiki/Radial_basis_function_network" rel="nofollow">radial basis function networks</a> (RBFNs) for probability estimation by plugging the output of the RBFNs into the <a href="http://en.wikipedia.org/wiki/Logistic_function" rel="nofollow">Logistic function</a> are weights bet... | 38,080 |
<p>In the post <a href="http://stats.stackexchange.com/questions/11009/including-the-interaction-but-not-the-main-effects-in-a-model">here</a>, <strong>a contributor (dmk38)</strong> makes an interesting, and may I add a very commonsense observation, that to include or not to include the main effects in an interaction ... | 71,772 |
<p>I am looking for a R package that implements Incremental PCA (online version of PCA)</p>
<p>Is there anybody that knows a piece of code that implements such algorithm?</p> | 964 |
<p>Which visualization libraries (plots, graphs, ...) would you suggest to use in a standalone application (Linux, .Net, Windows, whatever). Reasonable performance would be nice as well.</p> | 71,773 |
<blockquote>
<p>Stata is unusual among commercial
statistics packages in allowing
user-written commands, distributed as
so called ado-files, to be
straightforwardly downloaded from the
internet which are then
indistinguishable to the user from the
built-in commands. In this respect,
Stata combines the... | 71,774 |
<p>How do we find out the long term and short term effect of estimators on AR model?</p> | 71,775 |
<p>Does RSS + ESS = TSS all the time?</p>
<p>I am thinking - does it hold if there is no intercept?</p>
<p>Does this apply for all regressions, or are there certain conditions that need to be met?</p> | 71,776 |
<p>If I have an underlying distribution of expected values, how do I normalize my observed values by this distribution? </p>
<p>Here is an example:</p>
<p>I am testing for a deviation from 50:50 (my Null expectation), but there some biases in the way data is collected, so I would like to normalize my results first. ... | 71,777 |
<p>How to prove $k(x_i,x_j)=e^{-(LR(x_i-x_j))^TLR(x_i-x_j)}$ is a valid kernel function or positive semi definite? </p>
<p>$x=(\mu,\lambda)^T$ and R is a 2x2 rotation matrix, L is a 2x2 diagonal scaling matrix with positive entries. Any idea is appreciated.</p> | 71,778 |
<p>I have a data set that is composed of point locations in a landscape, lets call this dataset X. Some of the points in data set X need to be grouped together because they "function" together as a single unit in space. Let's call this subset of data, set A; it has 20 points but only 6 groups. The remaining points are ... | 33,431 |
<p>I have a question that seems basic but I found two alternative answers online so I thought that I should ask for advice. I have an experiment where each subject makes decisions about target words in two conditions: the word can be either preceded by a related word (the <em>related</em> condition) or it can be preced... | 71,779 |
<p>I have a significant effect of interaction $AB$ in $Y = A + B + AB + covariate$</p>
<p>Is it possible to do a mediation analysis to see if $AB\rightarrow Y$ is mediated by $A\cdot covariate$?</p>
<p>Is it valid to interpret this as: the effect of $AB$ is mediated/explained by how $A$ interacts with $A$? </p>
<p>... | 71,780 |
<p>I would like to receive any advice on the following question:</p>
<p>If one wants to test that variances are homogeneous among a certain number of population samples a possibility is to use the Levene’s test.</p>
<p>But if I have several independent samples of each of those populations (for instance, collected at ... | 33,438 |
<p>I want to create my own covariance function based on squared exponential or Matern that treats each dimension differently i.e. having a hyperparameter for each dimension, not just ell. How do I need to modify existing to get this behaviour?</p>
<pre><code>% precompute distances
if dg ... | 33,439 |
<p>I am trying to relate data and results in <a href="http://www.itl.nist.gov/div898/handbook/pmc/section4/pmc436.htm" rel="nofollow">NIST website</a> with the formula defined in previous page from the same website. But I am missing something here:</p>
<ol>
<li><p>Does initial trend & season indices computation me... | 71,781 |
<p>I have daily data where the number of values changes with each day. I would like to calculate the weighted mean of this data, where days with more values are weighted higher than days with less.</p>
<p><strong>Conceptualized data</strong>:</p>
<pre><code> day1 day2 day3 day4
[3,1,2] [4,1,4,5] [4,5,... | 71,782 |
<p>I have a dataset with 975 observations from 112 different categories. The timespan of this dataset is 18 years. However, the data is unevenly spaced and even acquired:</p>
<p>While some categories have only 1 observation for these 18 years, some others have 25, almost2 per year. This makes trying to set the periodi... | 33,443 |
<p>I realize that <a href="http://en.wikipedia.org/wiki/Conjugate_prior" rel="nofollow">this Wikipedia page</a> provides the proportional form of the conjugate prior to the gamma distribution with unknown $\alpha$ and $\beta$ parameters, as well as the posterior values of $p$, $q$, $r$, and $s$, which are the hyperpara... | 33,445 |
<p>I am working on a method to detect a finite set of significant points of temperature change within a data series. Although my first pass does an okay job of detecting significant temperature transitions, the results are less than ideal when working with a noisy signal or weak temperature variance. </p>
<h2>Sample T... | 71,783 |
<p>I need to find out out how opinion probability (continuous variable varying between 0 and 1) influences clusters (categorical variable - 6 clusters). I am using Stata and I see two possibilities: to use logistic regression (<code>logit</code>) or multinomial logistic regression (<code>mlogit</code>).
In case of logi... | 71,784 |
<p>I'm trying to design an experiment using repeated measures ANOVA. I have one (possibly two) factors I want to test. I have 5 factor levels that I want to show that there is a difference between. I will have 8 subjects. So ideally, I would test each of the 5 factor levels on each subject (randomizing the order of cou... | 33,448 |
<p>I have done a simple clustering (protoclust) using error-containing data. To determine distances, I used a simple "pseudo-d" distance, in which the absolute value of the difference between two points was weighted by the inverse of the pooled error of the two points. This was for two variables. On the (somewhat unwar... | 33,449 |
<p>Here are 3 questions about the LOESS smoothing fit.</p>
<pre><code># Loess model
plot(Y ~ X)
loess.model <- loess(Dataset$Y ~ Dataset$X)
loess.model
hat <- predict(loess.model)
lines(Dataset$X[order(Dataset$X)], hat[order(Dataset$X)], col="red")
Number of Observations: 52
Equivalent Number of Parameters: ... | 71,785 |
<p>I am having some issues with using neural network. I am using a non linear activation function for the hidden layer and a linear function for the output layer. Adding more neurons in the hidden layer should have increased the capability of the NN and made it fit to the training data more/have less error on training... | 71,786 |
<p>I am evaluating some customer satisfaction data, and want to calculate how much each predictor variable contributes to the response (customer satisfaction). Ideally, I would use the Shapley Value Regression method, but that is unavailable on SPSS. I tried using semi-partial correlation, but the values are inaccurate... | 71,787 |
<p>Suppose that we have $1000$ cars. Also suppose out of a random sample of $300$ cars, $1$ of them fail. So the failure rate is $1/300$. Now we have $700$ cars left. To improve the failure rate, what is the additional number of cars that need to be tested? What is the failure probability? Can we model this with a expo... | 71,788 |
<p>Say I have a data set with 10,000 rows and the target is a binary variable with 1500 positives (1's) and 8500 negatives (0's). I run a model and get predictions on the 0-1 interval. My question is what's the best way to tell if my model is actually adding any value?</p>
<p>If the AUC is ~ to (1 - the positive % o... | 71,789 |
<p>I am new to time series modeling in R. I have sales data of one year and three months only. I am trying to do sales forecasting at the day level or max at the week level. Following is the step I intend to follow</p>
<ol>
<li>Convert it into time series object using <code>ts(data$qty, frequency= ??)</code>. Here I a... | 71,790 |
<p>I'm supposed to analyse the effect of a governmental health care program on mortality (cancer vs. cardiovascular desease vs. any other cause of death). Health care program started in 1975 and is still going on. Citicens are invited regularly (every 2 years) to use this health care program. To evaluate the effect of ... | 33,453 |
<p>Given two beta distributions $X \sim \beta(m_1, n_1)$ and $Y \sim \beta(m_2, n_2)$, how to compute the mode of the distribution of $Z = X - Y$?</p> | 71,791 |
<p>I would like to know what the distribution is of linear combinations of Poisson random variables.</p>
<p>I know that a linear combinations of Poisson random variables is not always a Poisson random variable, namely </p>
<p>$Y : = \sum_k a_k X_k$</p>
<p>with $X_k \sim Pois(\lambda_k)$. Now, $Y$ is only Poisson if ... | 71,792 |
<p>Ridge Regression can be expressed as $$\hat{y} = (\mathbf{X'X} + a\mathbf{I}_d)^{-1}\mathbf{X}x$$ where $\hat{y}$ is the predicted label, $\mathbf{I}_d$ the $d \times d$ identify matrix, $\mathbf{x}$ the object we're trying to find a label for, and $\mathbf{X}$ the $n \times d$ matrix of $n$ objects $\mathbf{x}_i = ... | 71,793 |
<p>I am trying to interpret the SPSS output from a multiple hierarchical regression where the intercept has been eliminated because it is not significant.</p>
<p>I have read previous discussions about inclusion/exclusion of the intercept in this forum and I have seen that the majority of the answers were against the e... | 71,794 |
<p>I have a real-time domain where I need to assign an action to N actors involving moving one of O objects to one of L locations. At each time step, I'm given a reward R, indicating the overall success of all actors.</p>
<p>I have 10 actors, 50 unique objects, and 1000 locations, so for <em>each actor</em> I have to ... | 33,455 |
<p>What relations and differences are between <a href="http://en.wikipedia.org/wiki/Statistical_learning_theory">statistical learning theory</a> and <a href="http://en.wikipedia.org/wiki/Computational_learning_theory">computational learning theory</a>?</p>
<p>Are they about the same topic? Solve the same problems, and... | 71,795 |
<p>What exactly is building a statistical model? </p>
<p>These days as I am applying for research jobs or consulting jobs, the term "building a model" or "modelling" often comes up. The term sounds cool, but what are they referring to exactly? How do <em>you</em> build your model?</p>
<p>I looked up <em>predictive... | 71,796 |
<p>I saw the Johnson family of distributions in context of reliability and demand modeling for supply chains, but I am not sure if they are bringing real benefit to pay for their relatively more complex format. What are their major features and when one should use them? </p> | 33,457 |
<p>I was reading this article related to generalized linear models: <a href="http://en.wikipedia.org/wiki/Generalized_linear_models" rel="nofollow">http://en.wikipedia.org/wiki/Generalized_linear_models</a>. It gave a specific example </p>
<blockquote>
<p>Ordinary linear regression predicts the expected value of a ... | 71,797 |
<p>Do we know anything about the tail distribution of sum of squares of a limited number of i.i.d exponentially distributed random variables? I'm looking for a good bound.</p> | 44,414 |
<p>I am trying to do my design of experiment for numerical simulations. Here, i have (eg.) 10 parameters which can be <code>0</code> or <code>1</code> resulting in an input like <code>[0,1,1,0,1,0,0,1,0,0]</code> for <code>[A,B,C,D,E,F,G,H,J,K]</code>. As the number of parameters (depening on my experiment) might rise ... | 33,461 |
<p>My question is about a homework question that I found interesting. It gives another proof (without using martingales) for that the critical Galton Watson tree dies out eventually. But it has given a recurrent relation which turns out to be tricky in the problem 5 (Part (a)) of the following problem set. Is there an... | 33,462 |
<p>I have been trying to estimate state space models using dlm package in R. The problem is that the model I am estimating requires inclusion of a few exogenous variables. I still can't figure out how to do it.
Does any one know how to add exogenous variables to a state space model in dlm package?</p> | 33,463 |
<p>If I use <em>linear model</em>, <em>generalized linear model</em>, <em>partial least squares</em> etc packages in R, and train it where, given key response variable <code>RSP</code>, the formula argument is of the form:</p>
<pre><code>formula <- as.formula("f(RSP)~A + B + C") # use A,B,C predictors only
</code><... | 33,464 |
<p>Correlation (r) is a measure of linear association between two variables. Coefficient of determination (r^2), is a measure of how much of the variability in one variable can be "explained by" variation in the other. </p>
<p>For example, if r 0.8 is the correlation between two variables, then, r^2 = 0.64. Hence, 64%... | 44,416 |
<p>I have a panel dataset that contains information on households and their purchases in specific weeks and even minutes of a week. For example, a household would purchase different brands of beer and record those purchases. If they buy 3 different brands of beer in one purchase, they would record each brand separately... | 32,936 |
<p>When data are a linear mixture of non-gaussian sources, it can be shown that with a rotation, an independent rescaling of each of the rotated axes, and a second rotation you can recover the original, independent axes. Singular value decomposition [SVD] does exactly these three operations -- i.e., it decomposes a ma... | 71,798 |
<p>I recently received a review back for a paper in which I referred to some previous studies as 'correlational' where they used multiple regression to analyze some population data and make biological conclusions (specifically a linear mixed effects regression). One reviewer made a very big deal about this, suggesting ... | 71,799 |
<p>I need help writing a SARIMA model I have obtained mathematically. My model is </p>
<p>ARIMA(1,0,4)(2,0,2) period 12. </p>
<p>I understand what the different parts actually mean but get very lost trying to write out the mathematical model. I have tried to follow other examples but as the models differ it makes it ... | 33,468 |
<p>I am working on a project for a Masters Project. The town I am looking at Switched to a Fareless system in Feb 1, 2011. I want to look and see if this increased ridership by a substantial amount. I have the following</p>
<p><img src="http://i.stack.imgur.com/07VnB.jpg" alt="Data"></p>
<p>for data and have it dr... | 33,472 |
<p>Suppose I have $4$ ordinal variables and a single covariate ($\log_{10}(x)$). When I run an ordinal probit model, I get three threshold coefficients and one probit slope. Call the threshold coefficients $b_1, \dots,b_3$ and the probit slope $b_4$. </p>
<p>So we can get $10^{b_1/b_4}$ for category 1, $10^{b_{2}/b_{4... | 42,217 |
<p>I am reading a bit on survival analyses and most textbooks state that</p>
<p>$h(t)= \lim_{ \Delta t \rightarrow 0} \frac{P(t < T \leq t+\Delta t |T \geq t )}{ \Delta t} =\frac{f(t)}{1-F(t)} (1)$</p>
<p>where $h(t)$ is the hazard rate, </p>
<p>$f(t)=\lim_{\Delta t \rightarrow 0} \frac{P(t < T \leq t+\... | 33,474 |
<p>I'm trying to figure out support vector machines using this <a href="http://www.tristanfletcher.co.uk/SVM%20Explained.pdf" rel="nofollow">resource</a>. On page 2 it is stated that for linearly separable data the SVM problem is to select a hyperplane such that $\vec{x}_i\vec{w} + b \geq 1$ for $y_i \in 1$ and $\vec{x... | 71,800 |
<p>I recently came across the paper <a href="http://www.artsci.wustl.edu/~jgill/papers/hypo.pdf" rel="nofollow">"The Insignificance of Null Hypothesis Significance Testing", Jeff Gill (1999)</a>. The author raised a few common misconceptions regarding hypothesis testing and p-values, about which I have two specific que... | 49,294 |
<p>Can you suggest a source (book, lecture notes, etc) that provides a good introduction to mixture modeling? I would like something that discusses (mixes?) theory and application at the graduate level. If it offers examples from the social sciences, even better. Thanks.</p> | 13,354 |
<p>Why does the rank of the design matrix $\boldsymbol X$ equal the rank of $\boldsymbol{X'X}$? Is this true in all circumstances? </p>
<p>If X is not linearly independent, what would the rank of X'X be?</p> | 71,801 |
<p>The formula for computing variance has $(n-1)$ in the denominator:</p>
<p>$\sigma^2 = \frac{\sum_{i=1}^N (x_i - \mu)^2}{n-1}$</p>
<p>I've always wondered why. However, reading and watching a few good videos about "why" it is, it seems, $(n-1)$ is a good unbiased estimator of the population variance. Whereas $n$ un... | 880 |
<p>The problem with gradient descent algorithms, e.g. the <a href="http://en.wikipedia.org/wiki/Levenberg%E2%80%93Marquardt_algorithm" rel="nofollow">Levenberg–Marquardt algorithm</a>, is that they will converge into a minimum that is nearest to the initial guess, so when starting from different positions you will end ... | 71,802 |
<p>Although reading quite a bunch of books, I'm still not sure, which method to use and how to implement it, therefore I appreciate any help! </p>
<p>I have 4 different groups (treatments) with 50 participants each. Each participant's action is observed 5 times under the same condition. The 5 different values are coll... | 33,482 |
<p>I am new to stats and didn't have the chance to take the course at university. However I do need to know the difference between Bayesian Networks & Markov Processes.</p>
<p>I found good material for both of them:</p>
<p><a href="http://vserver1.cscs.lsa.umich.edu/~spage/ONLINECOURSE/R10Markov.pdf" rel="nofollo... | 71,803 |
<h2>Background</h2>
<p>I have data from a field study in which there are four treatment levels and six replicates in each of two blocks. (4x6x2=48 observations)</p>
<p>The blocks are about 1 mile apart, and within the blocks, there is a grid of 42, 2m x 4m plots and a 1m wide walkway; my study only used 24 plots in e... | 71,804 |
<p>I have a general understanding of the difference between a population (set of entities under study) and a sample (a subsection selected from the population). However, I've been doing some work in PPC (Pay-Per-Click) and AdWords recently, and can't seem to grasp the population/sample difference in regards to that.</p... | 33,487 |
<p>Suppose I am given $n$ samples of sizes $N_1, \dots, N_n$ from a Dirichlet–multinomial distribution: Fixed and given is a $k$-vector $\mathbf{\alpha}$ of positive real numbers. For each $i, \, 1 \le i \le n$, a random probability vector $\mathbf{p}_i$ is drawn from a Dirichlet distribution $\mathrm{Dir}(\mathb... | 33,488 |
<p>I am looking at using the lasso as a method for selecting features and fitting a predictive model with a binary target. Below is some code I was playing with to try out the method with regularized logistic regression.</p>
<p>My question is I get a group of "significant" variables but am I able to rank order these ... | 71,805 |
<p>I have a question that pertains to time series or more likely pertains just to simple math. </p>
<p>Lets suppose that I am measuring the number of online visitors to 5 websites on a monthly basis, so I have this data for the months of Jan - Dec.</p>
<p>What I want to understand is "What is average <strong>yearly</... | 71,806 |
<p>Does anybody know how to arrange a cross validation so I can compare two models (negative binomial with quasi-Poisson)? I know some theory beyond cross validation, but don't know what kind of cross validation makes sense (leave one out, simple cross validation, k-fold) when comparing two glms with about 1000 observa... | 44,459 |
<p>Is it possible to take the log of an independent variable in a Poisson regression? What to I have to be aware of, when doing so? (The results are getting better, when assuming that the independent variable is with log link.)</p> | 33,489 |
<p>I am looking to do classification on my text data. I have <code>300 classes</code>, 200 training documents per class (so <code>60000 documents in total</code>) and this is likely to result in <strong>very</strong> high dimensional data (we may be looking in excess of <strong>1million dimensions</strong>).</p>
<p>I ... | 71,807 |
<p>Let's say I have the two following ARIMA models: </p>
<ol>
<li>ARIMA(7,1,1) (no seasonality) </li>
<li>ARIMA(6,1,1)(1,0,0)<sub>7</sub> (seasonality of period 7).</li>
</ol>
<p>Are they conceptually the same? If so, why is that when I model them using R, I get different models and different fits?</p> | 13,451 |
<p>I have a categorical independent variable (two levels: condition 1; condition 2) and ordinal(?) dependent variables (numerical magnitude shifts (e.g. -3 if there was a decrease in number magnitude from 4 to 1). I now want to assess whether the condition predicts a change in the dependent variable. It is a repeated m... | 71,808 |
<p>Evaluating a smooth object with <code>smoothCon</code> provides, besides several other things, the ordinary "untouched" spline bases </p>
<pre><code>objx <- te(x,bs="ps",k=4)
Con.mgcv.x <- smoothCon(objx,dat,knots=NULL,scale.penalty=FALSE)
Mx.mgcv <- Con.mgcv.x[[1]]$margin[[1]]
Mx.mgcv$X
</code></pre>
<p... | 71,809 |
<p>Assume that you have a regression with a whole set of variables and you know that the residuals are not normal distributed. So you just estimate a regression using OLS to find the best linear fit. For this you disclaim the assumption of normal distributed error terms. After the estimation you have 2 "significant" co... | 71,810 |
<p>I have tested a regression framework's robustness to noise and I have noticed in some cases that adding noise improves the prediction performance and in other cases the performance degrades.</p>
<p>What could be the reasons for this? If there are multiple reasons, how to I determine which is the cause?</p>
<p>Edit... | 44,467 |
<p><strong>The question</strong></p>
<p>I have a dataset which I think requires a multivariate multilevel analysis. I am unsure both of the appropriate model and of how to fit it with <code>R</code>. I have come up with a tentative model, but my understanding of the math is so superficial that I cannot tell whether my... | 71,811 |
<p>I'm trying to analyze an experiment, in which every subject is asked the same question in different conditions. I then describe each of their answers into categories describing their answers in detail.</p>
<p>I'm trying to find relations between different categories. For example, several users whose answers can be ... | 71,812 |
<p>I am trying to fit an HMM to a dataset resembling:</p>
<pre><code>id0: A, A, A, C, B, A, C, B
id1: C, B, A, A, C, C
id2: B, A, A, C, B, B, A
</code></pre>
<p>In total there are three characters (A, B, C) and about 40k of such rows. I'm using R's <code>HMMFit</code> from the <code>RHmm</code> package.</p>
<p>As in... | 37,915 |
<p>Why do we analyze residual plot in regression analysis and NOT between two individual variables?</p>
<p>For example when checking for normality, heteroscedasticity etc. we don't analyze two individual variables but residual plot, why so?</p> | 33,498 |
<p>I used regular logistic regression on my dataset and got a few significant hits. However, since the data is 1:1 case-control matched data I decided to try using conditional logistic regression (<code>clogit()</code> in the <code>survival</code> package of <code>R</code>). </p>
<p>However, none of the results are si... | 33,499 |
<p>I have fit a mixed model with <code>lmer()</code> and am left with 4 significant interaction terms. </p>
<p>There were found by removing the interaction term and comparing with the full model using <code>anova(fm1, fm2)</code>. I have also left the single terms in the model. </p>
<p>When I come to report the chi-s... | 33,500 |
<p>I am working my way through Chapter 4 (Tests) in Davison & Hinkley's (D&H's) book "Bootstrap Methods and their Applications", and have a question about one of their examples. </p>
<h2>Davison & Hinkley's proposed test</h2>
<p>Example 4.1 proposes a permutation test for the (alternative) hypothesis of n... | 71,813 |
<p>Say I have a bunch of weighted coins that should show heads 90% of the time. I take a bunch of them, throw them in a box, and calculate the percentage of coins that landed on heads. I do this a bunch of times and calculate a standard deviation of 5% and a mean of 90%.</p>
<p>Assuming a normal distribution, I then (... | 71,814 |
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