question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>Simplified version of my model:</p>
<pre><code>glm(cbind(young, adults) ~ as.factor(month) + effort, family = "binomial")
</code></pre>
<p>i.e., I study proportion of young as a dependent variable on month (or season), taking into account observer effort. However, the observer effort is dependent on the month:</p>... | 71,815 |
<p>Recently I have learned about <a href="http://en.wikipedia.org/wiki/Sequential_analysis" rel="nofollow">sequential analysis</a> especially <a href="http://en.wikipedia.org/wiki/Sequential_probability_ratio_test" rel="nofollow">sequential probability ratio tests</a> (after I have struggled a lot with cumulation of al... | 71,816 |
<p>Say I have eaten hamburgers every Tuesday for years. You could say that I eat hamburgers 14% of the time, or that the probability of me eating a hamburger in a given week is 14%.</p>
<p>What are the main differences between probabilities and proportions?</p>
<p>Is a probability an expected proportion?</p>
<p>Are ... | 71,817 |
<p>I would like to quantify the amount of uncertainty in a given message, but the signal I work with is non-stationary and non-linear.</p>
<p>Is it possible to apply Shannon entropy for such signal?</p> | 33,504 |
<p>I have two historical price lists with the following columns</p>
<blockquote>
<p><strong>data - price</strong></p>
</blockquote>
<p>Now i have to create the ratio between the prices of these lists:</p>
<blockquote>
<p><strong>list A:</strong> 01/01/2011 10.50</p>
<p><strong>list B:</strong> 01/01/2011 23... | 71,818 |
<p>I'd like to know if there is a boxplot variant adapted to Poisson distributed data (or possibly other distributions)?</p>
<p>With a Gaussian distribution, whiskers placed at L = Q1 - 1.5 IQR and U = Q3 + 1.5 IQR, the boxplot has the property that there will be roughly as many low outliers (points below L) as there ... | 71,819 |
<p>Following Hofert et al.'s paper "Likelihood inference for Archimedean copulas in high dimensions under known margins," (<a href="http://dl.acm.org/citation.cfm?id=2263953" rel="nofollow">http://dl.acm.org/citation.cfm?id=2263953</a>) I wrote a script in Matlab to produce estimates of Archimidean copulas in high dime... | 71,820 |
<p>I understand how EM is used in the sense of estimating the Gaussian model that underlies a set of data, but its unclear how this is applicable. </p>
<p>I am trying to understand how EM might be used to perform data mining on any sort of computer vision/image processing task. This is the domain I am most familiar w... | 71,821 |
<p>I am doing a project work in sentiment analysis (on Twitter data) using machine learning approach. In order to find the 'best' way to this I have experimented with naive Bayesian and maximum entropy classifier by using unigrams, bigrams and unigram and bigrams together. I'm using the <a href="http://sharpnlp.codeple... | 33,505 |
<p>My data (n > 4000) contains the results of two separate tests (instruments). I have a profile made from likert scales for one of the instruments (S1, S2, ... S20). I want to find the corresponding profile for the 2nd instrument that would correlate perfectly (or near perfectly) with the first instrument. It seems th... | 71,822 |
<p>I have following variables in my dataset:</p>
<ol>
<li>Working hours (numerical:ordinal)</li>
<li>Effectiveness (categorical:ordinal ; 4 values-> (poor,average,good,best))</li>
<li>Satisfaction (categorical:ordinal ; 4 values-> (poor,average,good,best))</li>
</ol>
<p>I want to cluster the data on the basis of how... | 71,823 |
<p>I have created a model of American cities with a dichotomous Y variable using logistic regression. I have theoretical reasons to believe that the model will differ significantly between larger and smaller cities. I have shown this using arbitrary breakpoints, but wanted to know if a segmented (piecewise) regression ... | 71,824 |
<p>First picture is the question and its answer key: </p>
<p><img src="http://i.stack.imgur.com/3qWCe.jpg" alt="enter image description here"></p>
<p>The second picture is my solution: </p>
<p><img src="http://i.stack.imgur.com/cIlt5.jpg" alt="enter image description here"></p>
<p>I know that $S^2=\frac{\sum(x_i-\b... | 71,825 |
<p>I am confused and struggling to read this simple crosstabs. </p>
<p><img src="http://i.imgur.com/NNdbMsP.jpg" alt="Crosstabs"></p>
<p>I am trying to create a profile of downloaders. One of the demographics I am looking at is age. Should I be looking at the percentage within Age or percentage within Type of downloa... | 33,512 |
<p>I want to analyze functional MRI (<a href="http://en.wikipedia.org/wiki/Functional_magnetic_resonance_imaging" rel="nofollow">fMRI</a>) data as follows:</p>
<ol>
<li><p>I am comparing the brain networks of two groups of subjects (patients and matched).</p></li>
<li><p>For each subject I have a correlation (Pearson)... | 37,539 |
<p>When should I use quadratic weighted kappa or linear weighted kappa?</p>
<p>I have two observers evaluating the classes of a number of objects. The classes are fail, pass1, pass2, and excellent (ordinal scale). The errors in classification between "fail" or "excellent" and the different degrees of "pass" are more s... | 71,826 |
<p>I'm trying to calculate a single breakpoint on $x$ from several thousand $(x,y)$ points. Due to the density distribution as per the 2D histogram below, the least squares method is proving unsuitable. An orthogonal regression is a much better fit for the lower $x$-axis, but is it possible to conduct a piecewise ortho... | 33,515 |
<blockquote>
<p><strong>Possible Duplicate:</strong><br>
<a href="http://stats.stackexchange.com/questions/12386/machine-learning-cookbook-reference-card-cheatsheet">Machine learning cookbook / reference card / cheatsheet?</a> </p>
</blockquote>
<p>Each classifier has it's own advantages and disadvantages. </p>... | 49,363 |
<p>Wikipedia says that the name of concept comes from physics, but I cannot find any similarity between these two concepts.</p> | 49,723 |
<p>I have a set of sessions and urls that have been accessed in each of these sessions and frequencies with which they have been accessed. I've put them in a matrix-like representation.</p>
<p>Imagine I have the following "Pageview matrix":</p>
<pre><code>COLUMN HEADINGS
books placement resources br aca
</code></pre... | 71,827 |
<p>It is said that if the plots of the hypothetical responses are not parallel, but crossed, there is interaction. Suppose we have two factors. Is it possible that the plots cross but we do not have interaction? That is more reasonable when the plots are close to each other.<br>
I noticed the converse is true. We may h... | 33,518 |
<p>My original question was going to be : How do you estimate the proportion of species in a population from count data of their individual body parts, provided that you can identify each part as belonging to a specific species. </p>
<p><strong>Is it just enough to take the average number of body parts found per speci... | 71,828 |
<p>I recently happend to read about empirical Bayes (some introduction by Cassella?)
and it looked a lot like random effects model; in that both have estimates shrunken to global mean...</p>
<p>But I havent read it throughly...</p>
<p>Does any one has any insight about the similarity and differences between them?</... | 33,520 |
<p>I am unsure which statistical tests I should use in order to follow-up my three-way interaction. I used to split my file and run the analysis twice per group, but as I read in the paper by <a href="http://dx.doi.org/10.3758/BRM.41.3.924" rel="nofollow">Hayes & Matthes, 2009, <em>Behavior Research Methods</em></a... | 37,703 |
<p>Classic agglomerative hierarchical clustering methods are based on a <a href="http://en.wikipedia.org/wiki/Greedy_algorithm" rel="nofollow">greedy algorithm</a>. This means that they (many of them) are prone to give sub-optimal solutions instead of the global optimum result, especially on later steps of agglomeratio... | 71,829 |
<p>Assume the sample ${(x_i)}_{i=1}^{n_1} \sim_{\text{iid}} {\cal N}(\mu, \sigma_1^2)$ is independent of the sample ${(y_i)}_{i=1}^{n_2} \sim_{\text{iid}} {\cal N}(\mu, \sigma_2^2)$. What are the available methods to get a confidence interval about the common mean $\mu$ ? In my case I have $n_1=n_2$. I would be satisfi... | 71,830 |
<p>In many papers I see data representing a rate of success (i.e a number between 0 and 1) modeled as a gaussian. This is clearly a sin (the range of variation of the gaussian is all of R),
but how bad is that sin? Under what assumptions would you say it is tolerable?</p> | 71,831 |
<p>Joshua Epstein wrote a paper titled "Why Model?" available at <a href="http://www.santafe.edu/media/workingpapers/08-09-040.pdf">http://www.santafe.edu/media/workingpapers/08-09-040.pdf</a> in which gives 16 reasons:</p>
<ol>
<li>Explain (very distinct from predict)</li>
<li>Guide data collection</li>
<li>Illuminat... | 33,528 |
<p>I have a question about using R to fit an AR model. If we want fit a AR(p) model, the equation will be $Y_t = φ_1Y_{t-1} + φ_2Y_{t-2} + ... + φ_pY_{t-p} + Z_t$.<br>
What about I only want to fit the model like $Y_t = φ_1Y_{t-1} + φ_{11}Y_{t-11} + Z_t$? ($Z_t$ is white noise).<br>
Does anyone know how to fit this mod... | 71,832 |
<p>We are building a system that helps a university and its potential students choose the right field of study.(excuse my study-related-vocabulary! I am not a native English speaker).</p>
<p>Applicants have many fields to choose from(not the same number of fields for every student).
Access to some fields is based on s... | 966 |
<p>Should one always expect the central tendency (i.e., mean and/or median) of a bootstrapped sample to be similar to the observed value? </p>
<p>In this particular case I have responses that are distributed exponentially for subjects across two conditions (I didn't run the experiment, I only have the data). I have ... | 71,833 |
<p>I have seen many papers using 10-fold CV ("10-pool" CV),
but I think the accuracy obtained this way can be,
sometimes, optimistically incorrect
since at any given time step <strong>t</strong> the sum of distinct queries of all folds
might be greater than <strong>t</strong>.</p>
<p><strong>t</strong> is normally use... | 71,834 |
<p>I have a two-dimensional data set that I would like to model as the outer product of two vectors (or two unit vectors times a constant). I need to find a way to a) figure out what these two vectors are and b) how well the data fits the model. The caveat is that I need to do this in the presence of possible missing v... | 71,835 |
<p>The response variable I'm dealing with is the proportion of a total area that is suitable habitat for a species of interest. So although the response variable is bounded between 0 and 1, my intuition is that it wouldn't be appropriate to call it binomial since the numerator and denominator of the proportion are non-... | 71,836 |
<p>Is it reasonable to use <strong>forward sampling</strong> to compute the probability of P(X_1=x_1, ..., X_N=x_n) in an HMM where is the observation variable?</p>
<p>Is the forward sampling algorithm related to the forward-algorithm for HMM?</p> | 33,530 |
<p>I don't have a strong math background, so I am kind of stuck trying to understand how RBMs work. On wikipedia page about RBMs, I am able to understand the formulas in isolation, however, I'm not sure how these formulas are connected together.</p>
<p>More specifically, isn't there cyclic dependency between energy f... | 33,531 |
<p>In
<a href="http://stats.stackexchange.com/questions/104780/required-method-of-moments-fitting-routine-for-the-two-parameter-generalized-pa">this thread</a>
the first two moments of the two-parameter GPD are given, where the distribution might be defined as</p>
<p>$G(y)= \begin{cases} 1-\left(1+ \frac{\xi y}{\beta... | 33,532 |
<p>I'm a beginner in statistics and I have to run multilevel logistic regressions. I am confused with the results as they differ from logistic regression with just one level. </p>
<p>I don't know how to interpret the variance and correlation of the random variables. And I wonder how to compute the ICC.</p>
<p>For exa... | 71,837 |
<p>I am interested in the way in which data are analysed in education. In England, pupils' reported test results are compared to national test results using z-tests. These results are then used to judge the effectiveness of schools. My hypothesis is that students in a school are not IID, and that therefore analyses usi... | 71,838 |
<p>I am by no means good in statistics, but I think I have come to the right place.
My question is simple:</p>
<p>My problem consists of comparing the population of several states in a small country, but some states have a population of 3000,000 and some a population of 2,000.<br>
I am painting it on a map, and the "i... | 33,535 |
<p>Positive stable distributions are described by four parameters: the skewness parameter $\beta\in[-1,1]$, the scale parameter $\sigma>0$, the location parameter $\mu\in(-\infty,\infty)$, and the so-called index parameter $\alpha\in(0,2]$. When $\beta$ is zero the distribution is symmetric around $\mu$, when it is ... | 44,520 |
<p>Suppose I have some stochastic process $X_t$. At each time $t$, I receive an estimated probability distribution for $x_t$, followed by an observation $x_t$. After receiving a set of observations ${x_1, \ldots, x_n}$, I want to go back and re-estimate the probability distribution for each $x_t$, $1 \le t \le n$. What... | 44,521 |
<p>Let's say $y$ is a linear function of $x$ and a dummy $d$. My hypothesis is that $d$ itself is like a hedonistic index of a vector of other variables, $Z$. I have support for this in a $MANOVA$ of $Z$ (i.e. $z_1$, $z_2$, ..., $z_n$) on $d$. Is there any way to test the <em>equivalence</em> of these two models:</p>
... | 33,536 |
<p>Christopher Manning's <a href="http://nlp.stanford.edu/~manning/courses/ling289/logistic.pdf">writeup on logistic regression in R</a> shows a logistic regression in R as follows:</p>
<pre><code>ced.logr <- glm(ced.del ~ cat + follows + factor(class),
family=binomial)
</code></pre>
<p>Some output:</p>
<pre><... | 71,839 |
<p>I read from my textbook that $\text{cov}(X,Y)=0$ does not guarantee X and Y are independent. But if they are independent, their covariance must be 0. I could not think of any proper example yet; could someone provide one?</p> | 71,840 |
<p>I am trying to generate random samples from a custom pdf using R. My pdf is:
$$f_{X}(x) = \frac{3}{2} (1-x^2), 0 \le x \le 1$$</p>
<p>I generated uniform samples and then tried to transform it to my custom distribution. I did this by finding the cdf of my distribution ($F_{X}(x)$) and setting it to the uniform samp... | 33,541 |
<p>This will sound weird, but I'm trying to calculate something that I don't know the name.</p>
<p>I want to calculate how big/low a variable is in relation to the others. Like Google webmaster tools says "your site loads in 3s, this is slower than 59% of sites". How can I calculate this?</p>
<p>For example, the poin... | 71,841 |
<p>In the "Regression to the Mean" chapter of "Thinking, Fast and Slow" by Daniel Kahneman, an example is given and the reader is asked to forecast the sales of individual stores given the overall sales forecast and the sales numbers from the previous year. For instance(the book's example has 4 stores, I use 2 here for... | 44,526 |
<p>I have a set of measurement with 95% Poisson confidence intervals, and I would like to subtract and multiply them and propagate the error. For example, I measured the copy number of a piece of DNA in a biological sample as 0.0268, 95% CI = 0.308-0.227. I know there are systematic biases in my measurement, ie issues... | 71,842 |
<p>This is the next step from a question I asked earlier. I've got two data frames: one focused on birth data, and one focused on winter weather events. The aim of my project is to discover whether there exists a simple correlation between extreme winter weather events (i.e. winter storms) and a spike in births nine ... | 71,843 |
<p>OK so I have a working code to do what I want but I am new to R and feel like my solution is very clunky and there is likely a more efficient way to get the same result.</p>
<p>I have a set of data that contain records with a date, city, and quality score. For each city and each date, I want to create an exponenti... | 71,844 |
<p>Suppose I've a random variable $X$ and a sample of it with size $N$. I count how many element of the sample fall in a specific range $a<x<b$ and I found $n$ entries, so if I use Poisson statistics I can say that the error on $n$ is $\sqrt{n}$.</p>
<p>Now suppose I've a function $f$, quite close to the unit fu... | 71,845 |
<p>What is a dimensionless indicator? I assume it refers to the fact that it is consistent in the way that it doesn't vary disproportionately at the variation of its factors.</p> | 24,672 |
<p>I have data on the first to fourth moments of a continuous random variable and I am trying to find what distribution best fits the data. Wikipedia has a list of about 20 distributions that could fit the data and I would like to try each of them to see which is the best. Some of these distributions have one parameter... | 71,846 |
<p>Here's a series of data I'm observing:</p>
<pre><code>1, 1, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1, 1, 1
</code></pre>
<p>How do I use math to predict whether the next number in the series will be a 1 or a 0?</p> | 71,847 |
<p>In a multivariate context, that is with at least X or Y being a random vector, are there formulae or theorems that link (even remotely) the forward and inverse regression, $\text{E}(X|Y)$ and $\text{E}(Y|X)$ ?
Or alternatively $\text{E}(X_i|Y)$ and $\text{E}(Y|X_i)$, where $X_i$ is a given component of $X$.</p>
<p>... | 71,848 |
<p>Emerson, J. D. (1991) Graphical Display as an Aid to Analysis, in <em>Fundamentals of Exploratory Analysis of Variance</em> (eds D. C. Hoaglin, F. Mosteller and J. W. Tukey), John Wiley & Sons, Inc., Hoboken, NJ, USA. <a href="http://dx.doi.org/10.1002/9780470316832.ch8" rel="nofollow">doi: 10.1002/9780470316832... | 33,546 |
<p>I'm looking at a time series which has a very strong daily cycle in it. However, on top of having a daily cycle in the actual values of the time series, it also has a very strong daily variance cycle.</p>
<p>I am wondering if I can meaningfully remove the 'variance trend' from my time series. I can calculate the 'a... | 33,551 |
<p>I am working on the following two models.</p>
<p>Logit: Binary outcome $y$ ($y=1$ if paid more than the item value to win the item, $y=0$ otherwise)
$$
y=b_0+x_1b_1+x_2b_2+x_3b_3.
$$</p>
<p>OLS: Continuous dependent variable $z$ (amount of overpayment)
$$
z=b_0+x_1b_1+x_2b_2+x_3b_3+e.
$$</p>
<p>My questions:</p>
... | 33,552 |
<p>I was doing some NLP related stuff which involves training a hidden Markov model, and use the model to segment sentences. For every sentence, I translate the tokens into feature vectors. The features are manually picked by me, and I can only think of 20 features temporarily. All of the features are binary. So an exa... | 71,849 |
<p>I want to test a series of hypotheses on linear combinations of coefficients for logistic regression on categorical count data implemented as a GLM model. I know how to do linear combinations under normality, and I know how to do basic confidence intervals and significance tests for logistic models. But I just real... | 71,850 |
<p>Working with a 2D sensor. A row consists of 4096 samples, of which there are 16 <em>reference</em> samples (the rest are <em>active</em>). The reference samples do not measure the signal, but are used to estimate the unique measurement offset that affects the entire row. The measurements must be corrected by this ... | 33,554 |
<p>I <a href="http://stats.stackexchange.com/a/22511/2921">read on this site</a> that apparently the Kinect uses the <a href="https://en.wikipedia.org/wiki/Random_forests">random forests algorithm</a> for machine learning in some way. Can anyone explain what it uses random forests for, and how their approach works?</p... | 71,851 |
<p>I am a beginner to time-series analysis. I have the model below; y is sales of product and x is tweet-rate:</p>
<p>$y_t=ay_{t-1}+by_{t-2}+...+cy_{t-m}+dx_t+ex_{t-1}+...+fx_{t-n}$</p>
<ol>
<li>What is this model called? I guess it's called an AR model but I am not
sure since the dependent variable y is on R.H.S as ... | 33,557 |
<p>At my college I am doing a lot of testing, such as testing for autocorrelation, White , DW, $t$, $F$ etc.</p>
<p>However, I always have to look up, when to reject and when to accept for example $H_0$</p>
<p>Hence, I was wondering if there is a generalization for interpreting a statistical test such as:
When $value... | 71,852 |
<p>Say you have a random variable $X$ (e.g., kilometers driven). Getting its variance is straightforward. But what if you want to say, $A$ percent of the variance in $X$ is due to $\text{Var}(X)$ for female drivers and $B$ percent is the rest, that is, $\text{Var}(X)$ for male drivers? $A + B$ should be 100 percent.</p... | 71,853 |
<p><strong>Background:</strong> I read one article where authors report Pearson correlation 0.754 from sample size 878. Resulting p-value for correlation test is "two star" significant (i.e. p < 0.01).
However, I think that with such a large sample size, corresponding p-value should be less than 0.001 (i.e. three s... | 71,854 |
<p>I've been reading about the <a href="https://en.wikipedia.org/wiki/Star_schema" rel="nofollow">star schema</a> (or dimensional) database structure, which puts all measurements main in 'facts' table, and all context for those measurements in 'dimension' table linked to the facts table (I'm doing a horrible job explai... | 71,855 |
<p>I'm trying to fit a model estimating waiting time using negative binomial regression, but I'm not sure how to assess the goodness of fit for my model. I would like to compare the negative binomial model to a Poisson model. I have approximately $4,000$ data points. Any suggestions?</p>
<p>Thanks!</p> | 71,856 |
<p>I have heard it said that longitudinal and cross-sectional studies are forms of observational studies. </p>
<p><strong>Why can't longitudinal and cross-sectional studies be considered "controlled studies"?</strong></p>
<p>By their definitions, I think they can.</p> | 33,560 |
<p>Is $||Y-X\beta||_2^2 + \lambda\beta^T K\beta$ , the standard loss-function in kernel ridge regression, or is it different? Also, is the gaussian kernel a standard choice used for the kernel, in practice? If not, which kernels are used more often than not? Also, is $\lambda$ the only parameter to be tuned via cross-v... | 71,857 |
<p>I am trying to find a way to merge data that correspond to users and have the form</p>
<p>$user_i, property_1, property_2, .\dots, property_n$, where $n\geq50$, $i\geq 10^6$</p>
<p>We might have missing data in some cases (i.e. $property_k$ might be missing for some users), or we might have two or more users (line... | 71,858 |
<p>I’m trying to find a way to measure how much a single variable ‘summarizes’ a full set of continuous variables. For instance, in a PCA the first principal component will explain a certain percentage of the total variability in a multivariate set. So, how can I obtain a similar measurement for a pre-existing (untran... | 71,859 |
<p>Why is the test statistic of a likelihood ratio test distributed chi-squared?</p>
<p>$2(\ln \text{ L}_{\rm alt\ model} - \ln \text{ L}_{\rm null\ model} ) \sim \chi^{2}_{df_{\rm alt}-df_{\rm null}}$</p> | 33,563 |
<p>"Bootstrap validation"/"resampling cross-validation" is new to me, but was discussed by the answer to <a href="http://stats.stackexchange.com/questions/11602">this question</a>. I gather it involves 2 types of data: the real data and simulated data, where a given set of simulated data is generated from the real data... | 44,541 |
<p>I have a general, presumably simple, question, but I couldn't find a conclusive answer so far. </p>
<p>Assume I have a simple case of a General Linear Model with one categorical predictor variable, that has 3 levels. This corresponds to a one-way ANOVA with 3 groups. </p>
<p>The Linear Model would then be: $Y_i = ... | 36,772 |
<p>This is just an example that I have come across several times, so I don't have any sample data. Running a linear regression model in R:</p>
<pre><code>a.lm = lm(Y ~ x1 + x2)
</code></pre>
<p><code>x1</code> is a continuous variable. <code>x2</code> is categorical and has three values e.g. "Low", "Medium" and "High... | 71,860 |
<p>The hellinger distance for a univariate distribution is </p>
<p>$$
\ H(x) = 1 - \int\ \sqrt {f(x)g(x)} dx
$$</p>
<p>I wish to use it for a bivariate distribution, by extending it to this form</p>
<p>$$
\ H(x) = 1 - \int\ \sqrt {f(x, y)g(x, y)} dx dy
$$</p>
<p>Can someone comment on whether this is still a vali... | 33,567 |
<p>I have a set of observations of credit loss data, where the mean is 37% and variance 25%. Now, I have to find the distribution and the base assumption is it will follow a beta distribution. the issue is that my alpha and beta derived from mean and variance is being estimated at -0.025012 and -0.042588. I dont unders... | 33,568 |
<p>I have a logit model that comes up with a number between 0 and 1 for many cases, but how can we interprete this? </p>
<p>Lets take a case with a logit of 0.20</p>
<p>Can we assert that there is 20% probability that a case belongs to group B vs group A? </p>
<p>is that the correct way of interpreting the logit val... | 71,861 |
<p>I'm analyzing the residuals from a regression model fit to a dataset that covers several years worth of data. I want to report the sum of the residuals from that model, by year, as a measure of how the overall error for each year changes over time.</p>
<p>Is this an acceptable way to report residuals?</p>
<p>Here... | 19,860 |
<p>As per gung's advice in <a href="http://stats.stackexchange.com/questions/107520/getting-the-equation-from-rs-lm-when-using-a-product/107521">Getting the equation from R's lm when using a product</a>, I am starting a new thread for this question.</p>
<p>I have a model $\widehat{\log z} = a + bx + cy + dxy$ for ... | 71,862 |
<p>I am performing Box ´s test for equality of covariance matrices and I need to compute log(det(S1)) and log(det(S2)), where S1, S2 are sample covariance matrices with nearly zero determinant. How can I improve S1 and S2 in order to get non-zero determinant? I have 24-dimensional data with 14 observations. </p>
<p>T... | 71,863 |
<p>I am studying a complex system. My goal is to understand the impact of a spreading accident (which saturates the filter (sand and plant) and creates puddles). Puddles decrease the efficiency of the system (depollution of effluent, and moisture content). The impact on the efficiency will decrease with time (more or ... | 71,864 |
<p>Respected Fellows.
I will thankful if someone help me to explain my model results.my model is as follows.
Yit=αPFit+βPSit+δ (PF*PS) it+εit
Where Y is GDP per capita
PF=Political Freedom Index ranges from (0-10)
PS is political stability Index ranges from (0-10)
PF*PS=interaction term
I=country and t represent tim... | 71,865 |
<p>I would appreciate some advise on an a problem I ran into.
I use SPSS for statistical analysis of a study.</p>
<p>The study look into how a blood test predicts mortality with patients followup of 1 year. Patients were divided into quartiles, and using the first quartile as a reference group I used Cox regression to... | 71,866 |
<p>The formula used to compute a confidence interval for the mean of a normal population when n is small is the following. </p>
<p><img src="http://i.stack.imgur.com/Rm63b.gif" alt="http://i.imgur.com/vluLbC3.gif"> </p>
<p>What is the appropriate t critical value for each of the following confidence levels and sample... | 71,867 |
<p>I am currently trying to fit a survival analysis model which has the following survival function:</p>
<p>$S(t) = \lambda_i e^{-\lambda_i t}$</p>
<p>but with </p>
<p>$\lambda_i = e^{\beta_0 +\beta_1 log(1+X_i)}$</p>
<p>where $X_i$ represents each unique observation. </p>
<p>I am trying to use the default surviva... | 71,868 |
<p>I have two sets of hazard ratios (with confidence intervals), one comparing risk of developing a cancer between current smokers and never smokers, and another comparing former smokers to never smokers. I do not have the raw data. Is there a way to use this information to create a hazard ratio comparing current smoke... | 71,869 |
<p>What do the <strong>vertical bars</strong> mean in the first and third formulae?</p>
<p>$$v_i|z_i=k,\mu_k\sim\mathcal{N}(\mu_k, \sigma^2)$$
$$P(z_i=k)=\pi_k$$
$$\pi|\alpha\sim \text{Dir}(\alpha/K1_K)$$
$$\mu_k\sim H(\lambda)$$
This formula is originally from <a href="http://en.wikipedia.org/wiki/Dirichlet_process" ... | 71,870 |
<p>I was wondering if someone could help me regarding the statistical tests I should use. Basically I have the following:</p>
<p>1) I carried out a survey asking teachers and students to rank components in my conceptual framework using the the scale: </p>
<p>(not important) 1 2 3 4 5 (essential)</p>
<p>2) ... | 71,871 |
<p>The empirical process $B_n(x) = \sqrt{n}(F_n(x) − F(x))$ converges weakly to a zero-mean Gaussian process, $B$, with covariance function:</p>
<p>$\mbox{cov}(B(x), B(y)) = F(\min\{x, y\}) − F(x)F(y)$.</p>
<p>How I can prove this assumption (about covariance function)?</p> | 41,132 |
<p>On page 19 of the textbook <a href="http://www-bcf.usc.edu/~gareth/ISL/" rel="nofollow">Introduction to Statistical Learning</a> (by James, Witten, Hastie and Tibshirani--it is freely downloadable on the web, and very good), the following is stated:</p>
<blockquote>
<p>Consider a given estimate $$\hat{Y} = \hat{f... | 71,872 |
<p>I'm trying to understand how to interpret log odds ratios in logistic regression. Let's say I have the following output:</p>
<pre><code>> mod1 = glm(factor(won) ~ bid, data=mydat, family=binomial(link="logit"))
> summary(mod1)
Call:
glm(formula = factor(won) ~ bid, family = binomial(link = "logit"),
dat... | 49,549 |
<p>I am working on a project where I am evaluating software packages. I have got the results of two experiments where only one variable has been changed. Each experiment has been conducted 10 times. I am doing paired-sample t-tests. For some of my metrics, the results are exactly the same for the ten iterations. Theref... | 71,873 |
<p>Maybe the dumbiest question ever posted on CV:</p>
<p>I want to analyze the relationship between proportion data and some covariates in a generalized linear (mixed, but I don't think it matters) model.</p>
<p>The natural distribution to use would be binomial but most of the proportions are close to 0 and their dis... | 71,874 |
<p>I'd like to know if I understood correctly the following. In the <code>fit.variogram</code> method of the gstat library, there is a <code>fit.method</code> argument. In the documentation, it says that:</p>
<blockquote>
<p>The default method uses weights
$N_h/h^2$ with $N_h$ the number of point pairs and $h$ the... | 71,875 |
<p>What are the standard techniques of plotting a statistical ensemble of sequences?</p>
<p>I know the chaos game representation:</p>
<ul>
<li>H. Joel Jeffrey (1992), <a href="http://dx.doi.org/10.1016/0097-8493%2892%2990067-6" rel="nofollow">Chaos game visualization of sequences</a>. Computers & Graphics 16 (1):... | 71,876 |
<p>in my ANCOVA analysis, I have the case that my Y and X show a nonlinear pattern. Transforming either only Y or X does not help to stabilize variance. I did not find any hint that doing an ANCOVA in log-log space is illegal, however, I also did not find any note on that one should try out a transformation of Y AND X... | 33,582 |
<p>I need to do a unit root test with my panel data. I have 1500 firms from 98-2000. I want to examine if my LOGwage variable has unit roots or not. When I xtset my panel Firm and year, stata said that it's strongly balanced. But when I do the test xtunitroot llc wage if FirmID, it gives me "Levin-Lin-Chiu test require... | 71,877 |
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