question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I'm familiar with the use of auto-regressive models when it comes to forecasting a single vector of time-series data. Is anybody familiar with a more traditional modeling approach, i.e. - creating sets of features such as indicators for day of the week, time of the day, day of the month, holiday, and then running a ... | 31,608 |
<p>I am working on problems in the field of medical imaging where the need for a simple and interpretable model is important from a clinical perspective. This means that I have to explain the algorithm's prediction to non-experts (well non-experts in Mathematics).</p>
<p>My questions is twofold:</p>
<ol>
<li><p>As fa... | 70,561 |
<p>Could someone explain to me the difference between a periodogram and spectral density diagram?</p>
<p><img src="http://i.stack.imgur.com/0Z3SB.png" alt="enter image description here"></p>
<p>The first diagram is produced with this block of code:</p>
<pre><code>FF = abs(fft(datalist)/sqrt(128))^2
f = (0:63)/128
pl... | 31,610 |
<p>Assuming I observe, in a unit square, $n_1$ circles of area $A_1$ (non-overlapping amongst themselves) and $n_2$ circles of area $A_2$ (again, non-overlapping) and that each of the centres is uniformly distributed across the square (well, I guess that can't be precisely true given the non-overlapping constraint), is... | 70,562 |
<p>I'm looking to the different methods of representing a text into a machine-readable format.
However, until now, I only found "Bag of Words" approachs with a lot of variations (boolean BoW, weighted BoW, Bag of Topics...).</p>
<p>What is troubling me is that these methods don't take context into account (some approa... | 31,611 |
<p>Kindly recommend some teaching material for "design and analysis of experiments" for the students of biostatistics and epidemiolody. Pls note that the students have only little knowledge on statistics. It will be useful if the book contains many applications rather than theory.</p> | 70,563 |
<p>A quick recap for what I want to do, I want to determine if a text is written by the same author or not. Thus I use one-class classification.
<br>In my training set (18 samples), it looks like this (for simplifying, I used x as data value):</p>
<pre><code>1 1:x 2:x "until" 200:x
1 1:x 2:x "until" 200:x
</code></pr... | 70,564 |
<p>I have a table where </p>
<pre><code>Field1 = Name {John, Mark, Brian} and
Field2 = Ball Color {Red, Orange, Yellow}
</code></pre>
<p>Each person has 6 balls of different colors so for example here are all the records for John and Mark:</p>
<p><strong>Name</strong> <strong>Ball Color</strong></p>
<p>John Re... | 70,565 |
<p>I am using repeated 10-fold CV to calculate the accuracy of my ordinal regression model. I have 6 predictors, 10 ordered response categories, and a total of 1166 data points. </p>
<p>For the ordinal model, I have defined accuracy as <em>1 - loss</em>, with <em>loss</em> being a simple linear function of the distanc... | 70,566 |
<p>I have some hyperspectral image data similar to <a href="http://www.nature.com/nphoton/journal/v3/n11/images/nphoton.2009.205-f3.jpg" rel="nofollow">this</a>, and I want to do a PCA on it.
The problem: I've never done a PCA, and its specially difficult for me to do it on 3D data. </p>
<p>How can I do it in MATLAB ... | 70,567 |
<p>I'm working with count data (ticket sales, to be specific) and I'm having trouble fitting a model to it. I've tried a linear one and a transformed linear one, but the residuals end up being non-normal and having a non-constant variance. I've been trying to play around with other models (negative binomial, poisson, e... | 1,027 |
<p>When training my algorithm, if I can get some i.e. data my future test data that has no labels can it improve my algorithm's efficiency, is there any mathematical proof for it?</p>
<p>PS: I think semi-supervised methods and transductive learning are something similar to what I look for.</p> | 70,568 |
<p>Suppose I have a set of points $Y$, $X$ and I model them by using a Gaussian process $\mathcal{GP}(m,K)$. Let the noisy observations be given by</p>
<p>$$y^i = f^i + \sigma^2$$</p>
<p>$p(f)$ gives the prior on the Gaussian process. Then what will be the posterior $p(f|Y,Z)$ which is again a Gaussian process with a... | 31,618 |
<p>Suppose I have two scientific approaches to measuring the same physical quantity taking values between $[0,1]$. One (say method A) is generally accepted to be more accurate under certain conditions, but it is more of a gross measure (low spatial resolution). The other method is newer in the field, has the a higher r... | 70,569 |
<p>This question came up in an archaeology class, and it seems like it should be something very basic.</p>
<p>Suppose I want to count the number of marbles in a large bucket of sediment. I only have the manpower to process 20 liters of sediment in total.</p>
<p>Is it better to take:<br>
20 samples of 1 liter each<br>... | 70,570 |
<p>It seems quite common to see scientific researches using a summated score to represent an overall scale that consists of many individual scale items (ex. Likert scale items). I assume that regular statistical tools (ex. ANOVA, linear regression, etc.) can be used on these data, which are treated as quantitative dat... | 31,620 |
<p>Does a high LL value imply that the model has a high R^2? I'm a very beginner to statistics so please excuse my naivete.</p> | 70,571 |
<p>What does it mean to "condition on the margin of ____"? I lack statistical/mathematical training and phrases like these leave me bewildered and unsure where to look.</p>
<p>In this post (<a href="http://stats.stackexchange.com/questions/51028/which-are-differences-between-the-hypergeometric-distribution-and-chi-squ... | 70,572 |
<p>I've run a 2-way ANOVA on growth rate data (grams/day) with the factors of year type (good and poor) and site (A and B). Though the data themselves are non-normal and do not have homogeneous variances, the residuals fall pretty nicely along the qq plot, and they are not heteroskedastic. Running the test shows that t... | 70,573 |
<p>I am attempting to use a significant autocorrelation (where it lies outside a 95% interval around 0) indicating periodicity of a signal and use it as predictive variable in a regression.</p>
<p>If, for example, there's a significant autocorrelation at frequency 3, does this mean that I can use the time series as pr... | 70,574 |
<p>I have been exploring the use of neural networks to identify relationships between large numbers of differing species and the presence of a specific bacteria in the environment. Previously I had been using mixed effects models, as I could account for spatial autocorrelation in my data.</p>
<p>I was wondering howeve... | 31,624 |
<p>According to <a href="http://www.guttmacher.org/pubs/fb_contr_use.html" rel="nofollow">multiple</a> <a href="http://www.cdc.gov/reproductivehealth/unintendedpregnancy/contraception.htm" rel="nofollow">sources</a>, the probability that, after one year of typical use, a woman who uses male condoms will get pregnant is... | 70,575 |
<p>I am using RJAGS to simulate the posterior distribution of event that a certain candidate will win the presidential election. I need to find the actual percentage that one of the candidates will have. What I do have is the values of each iteration for each of my three chains for both the proportion of the first cand... | 18,210 |
<p>My question concerns estimation of “peer effects“ or “neighborhood effects” in a multilevel framework. The idea of such an effect is that the behavior of a household (on level-1) is influenced by the behavior of others in the same cluster/neighborhood (level-2) who are perceived as peers. Manski (1995:127) termed th... | 70,576 |
<p>I was hoping to get some help. In understand how to compute an exact numerical solution (<a href="http://www.cs.berkeley.edu/~jordan/courses/260-spring10/lectures/lecture5.pdf" rel="nofollow">http://www.cs.berkeley.edu/~jordan/courses/260-spring10/lectures/lecture5.pdf</a>) for the following Bayesian model:
$$ \tau ... | 36,462 |
<p>I asked a question similar to this previously:</p>
<p><a href="http://stats.stackexchange.com/questions/99282/check-that-state-space-model-implemented-correctly">Check that state space model implemented correctly</a></p>
<p>However I think I have a better handle on it now and want to re-ask it:</p>
<p>I simply wa... | 31,628 |
<p>I'm trying to use a LASSO model for prediction, and I need to estimate standard errors. Surely someone has already written a package to do this. But as far as I can see, none of the packages on CRAN that do predictions using a LASSO will return standard errors for those predictions.</p>
<p>So my question is: Is th... | 70,577 |
<p>There is a normality assumption when it comes to consider OLS models and that is that the errors be normally distributed. I have been browsing through Cross Validated and it sounds like Y and X don't have to be normal in-order for errors to be normal. My question is why when we have non-normally distributed errors i... | 70,578 |
<p>I am building a predictive model for the growth of the amount of users of a new p2p protocol inspired by bitcoin and I would like to use historical data collected from the growth of major social networks in my model. My specific questions are the following:</p>
<ol>
<li>Does a public database exist containing growt... | 30,130 |
<p>I apologize if this question has been done to death, but as a non-statistician I really don't know what is the bottom line takeaway. I am looking at a sample of 30,000 individuals who were the subject of an economic intervention. This intervention produces a mean increase in the annual income of the subjects of $200... | 31,630 |
<p>Any recommendations for choice of a constrained optimization library suitable for my optimization function? I am minimizing a i) non-linear function with linear equality and inequality constraints, and ii) have available the gradient and the hessian of the function. </p>
<p>If it helps, the function I am minimizing... | 70,579 |
<p>I have 4 data sets, each with thousands of records/instances. There are 2 factors. One factor has 3 instances at each factor level (there are thousands of levels in the data set). The other factor also has thousands of levels, but with varying numbers of instances at each level. For each factor, I would like to ... | 70,580 |
<p>What is the Likelihood function of a linear probability model?</p>
<p>I know the likelihood function is the joint probability density, but how to construct the likelihood function when we only have the probability $P(Y_i=1|X_i)$ and $P(Y_i=0|X_i)$?</p> | 42,182 |
<p>I am having difficulty finding information on the assumptions for the intraclass correlation. Can someone please tell me what they are?</p> | 42,184 |
<p>I have a sample that consists of 50 observations. The base model of the OLS-Regression with three control variables, two of them significant, has a $R^2=0.50$ and its F-Value is 7. Both <code>–ovtest</code> and <code>–linktest</code> (Stata 10.0) indicate no model misspecification. </p>
<p>I am testing four Hypothe... | 70,581 |
<ul>
<li>When dichotomising variables, what information is lost in the process? </li>
<li>How does a dichotomisation help in the analyses?</li>
</ul> | 31,637 |
<p>I have studied some of these <a href="http://stats.stackexchange.com/questions/3294/resources-for-learning-markov-chain-and-hidden-markov-models">resources</a> and I know that there is an R package called <a href="http://cran.r-project.org/web/packages/HMM/index.html" rel="nofollow">HMM</a>. Could anybody explain th... | 70,582 |
<p>I have been trying to interpret the results below, but I am finding it difficult. I wonder if someone could help me. All answers highly appreciated.</p>
<blockquote>
<p>Number of obs = 30<br>
F( 2, 27) = 19.73<br>
Prob > F = 0.0000<br>
R-squared = 0.5937<br>
Adj R-squared = 0.5637</p>
</blockquote> | 49,756 |
<p>I have questions about a study I was reading. In this study about children and money, the relationship between the age of the children and their weekly pocket money was assessed. The researchers studied the relationship between age and pocket money on a scatter plot and added a linear regression model. </p>
<ul>
<l... | 70,583 |
<p>I want to calculate the percentage of workers getting wages between $22$ and $58.$ I don't know what to use. Please help me.
I've learned central tendency and interpolation.</p>
<p>$$\begin{cases}Wages&&No~of~Workers\\0-10&&20\\10-20&&45\\20-30&&85\\30-40&&160\\40-50&&am... | 70,584 |
<p>I'm trying to run a tree-way repeated measures ANOVA on the following data: I have a completely balanced design with three within-subject factors (type, form and ch - channel) and one dependent variable amp (amplitude).</p>
<p>I'm inclined to believe the results I got using <code>aov</code> function:</p>
<pre><cod... | 70,585 |
<p>I have heard that larger sample sizes in randomised trials lead to a smaller possibility of confounding. </p>
<ul>
<li>Why is this true in the case of <strong>randomised trials</strong>?</li>
<li>Also, how does sample size of an <strong>observational study</strong> affect confounding?</li>
</ul> | 37,990 |
<p>I was trying to understand MDP's in the context of reinforcement learning, specifically I was trying to understand what the reward function explicitly depends on.</p>
<p>I have seen a formulation of the reward function as defined by Andrew Ng in his <a href="http://cs229.stanford.edu/notes/cs229-notes12.pdf" rel="n... | 70,586 |
<p>I'm working on a R data frame, such as:</p>
<pre><code>- column 1 : ID
- column 2 : count of event 1
- column 3 : count of event 2
</code></pre>
<p>(1 unique ID per row)</p>
<p>I try to compare the proportion of events 2 among events (1+2) across all IDs.</p>
<p>For now, I am just plotting the proportion e... | 70,587 |
<p>I implore the good people to quickly glance through this thread over at <a href="http://stackoverflow.com/questions/22060675/r-monte-carlo-integration-using-importance-sampling">StackOverflow</a> to get a better idea of my question if the following isn't clear.</p>
<p>I have these integrals to evaluate using Import... | 31,641 |
<p>I used R to estimate a regression with both numeric and categorical variables, and obtained coefficient estimates. </p>
<p>However, when I try to make predictions using new data, there appear to be some problems with dimensions. </p>
<p>Is there anything that must be done to the code so that R handles both types o... | 31,642 |
<p>I have a pdf that I need to sample from, but I'm having numerical issues and was hoping someone could provide some insight. My pdf is a product of gaussians</p>
<p>$$ P(\theta |d ) = \prod_{i=1}^{N} C_{i} e^{-\frac{1}{2 \sigma_{i}^{2}}(d_{i} - y_{i}(\theta) )^{2} } \,. $$ </p>
<p>Lets say for instance that $\t... | 2,489 |
<p>I would like to calculate the following conditional probability:
I know that the probability of a BLUE ball being drawn is 0.3.
I receive a message from A or B who saw the ball that has been drawn.
This person tells me that the ball drawn is BLUE.
I know the probabilities:</p>
<p>A observing BLUE and sending BLUE- ... | 70,588 |
<p>I have been reading <a href="http://www.powells.com/biblio/61-9780387848570-1" rel="nofollow">Elements of Statistical Learning</a>. And I saw some example R codes written online. </p>
<p>I realise that very often the explanatory variables $X$ (the data of the predictors) are standardised to '<em>zero mean and unit ... | 31,644 |
<p>I had a discussion recently in which it was stated that Scotland <a href="http://www.bbc.co.uk/news/uk-scotland-24370331" rel="nofollow">having more universities in the top 200 per capita</a> than any other country is a good indication of the intelligence of the population of Scotland:</p>
<p><strong>NOTE: I am not... | 31,645 |
<h3>Context</h3>
<p>Let $\mathbf{x}_i \in \mathbb{R}^{100}$ and $\mathbf{z}_i \in \mathbb{R}^{20}$ be input vectors with the same corresponding target $\mathbf{y}_i \in \mathbb{R}^{25}$. </p>
<p>Using ridge regression we obtain two separate mappings, $\mathbf{A}_\mathbf{x}$ and $\mathbf{A}_\mathbf{z}$, such that</p>
... | 70,589 |
<p>My name is Hugh, and I'm a PhD student using generalised additive models to
do some exploratory analysis. </p>
<p>I'm not sure how to interpret the p-values that come from the MGCV package
and wanted to check my understanding (I'm using version 1.7-29, and have
consulted some of Simon Wood's documentation). I look... | 70,590 |
<p>I have a dataset from a cohort of 500 children under
15 years of age that were screened for measles antibody
titre. Each row in the dataset represents an individual
child. Covariates included in the dataset for each individual are: age, sex,
whether a child ever suffered from measles before (a binary outcome,
yes/no... | 70,591 |
<p>I'm reading in a paper "<em>the goal is to cluster data in a way that is meaningful and at the same time as orthogonal as possible to the given classification</em>"</p>
<p>Could someone have any idea how the notion of orthogonality is used in this case?</p> | 70,592 |
<p>EDIT: The <a href="http://cran.r-project.org/web/views/WebTechnologies.html">Web Technologies and Services</a> CRAN <a href="http://cran.r-project.org/web/views/">task view</a> contains a much more comprehensive list of data sources and APIs available in R. You can <a href="https://github.com/ropensci/webservices">... | 70,593 |
<p>This wiki page <a href="http://en.wikipedia.org/wiki/Simple_linear_regression" rel="nofollow">Simple linear regression</a> has formulas to calculate $\alpha$ and $\beta$. Could anyone tell me how to derive the formulas in weighted case?</p> | 70,594 |
<p>I have a predictive classification task and the end users want to
get <strong>initial</strong> understanding of:</p>
<ul>
<li>the quality (not specified further) of each data point in a data set</li>
<li>whether there are systematic patterns between data quality problems
(e.g. rows with missings values have also hi... | 70,595 |
<p>I just have 1500 data points in excel. However, I want to do a chi squared test to prove if the data is normaly distributed. </p>
<p>My question is: How to calculate the expected range for such a large data set?</p>
<p><strong>UPDATE</strong></p>
<p>How to calculate the relative frequencies for such a large data ... | 70,596 |
<p>Trying to learn some Python and SKLearn, but for my work I need to run regressions that use error distributions from the Poisson, Gamma, and especially Tweedie families. </p>
<p>I don't see anything in the documentation about them, but they are in several parts of the R distribution, so I was wondering if anyone ha... | 70,597 |
<p>Say I have outcome variable $Y_i$ and predictors $X_{i1}$ and $X_{i2}$ for some data point $i$. Wikipedia says that a model is linear when:</p>
<blockquote>
<p>the mean of the response variable is a linear combination of the parameters (regression coefficients) and the predictor variables.</p>
</blockquote>
<p>I... | 31,649 |
<p>What is the purpose of the ANOVA table? I once learned that you can only interpret the significance (p-value) of a multi-level discrete variable, or an interaction effect using the ANOVA table. Why? Why can't you use the p-value outputs of the regression? Why do people look at the ANOVA table in practice? </p>
<p>G... | 923 |
<p>I am doing a robust regression to predicted a left-skewed outcome. Do I still need to do a transform on my data before doing robust regression, or will that issue be taken care of by the robust method? If so, what transform would you recommend? When I plot my residuals after doing robust regression, they still look... | 70,598 |
<p>Trying to minimize the error from a probabilistic regression model which is composed of hierarchical KDE estimated PDFs. The top level is the result of 2-4 separate meta-PDFs from different data fields the combination of many of their own KDE estimated PDFs.</p>
<p>I'm trying to train weights affecting how much eac... | 70,599 |
<p>I have a data set which consists of binomial proportions, let's say the success rate of converting a customer depending on the advertisement, the customer age, and various other factors.</p>
<p>For some common combinations of covariates, I have a lot of data, and therefore the binomial proportion of successes has l... | 31,652 |
<p>This question is more to do with interpretation than calculation. I have a model which predicts the probability of a detector 'firing' under a certain intensity of signal, or actually in this case lack of a signal. The detector is made of a number of sub-pixels so the probability of none of the sub-pixels firing in ... | 70,600 |
<p>This is my first question on stats, just trying to learn the basics of time series analysis with <code>R</code>. So any good suggestions about learning resources will be highly appreciated as well as the answer to the question.</p>
<p>For the data below, let's say it represents number of website visits per day, I w... | 70,601 |
<p>What are the maximum-likelihood estimators for the parameters of Student's t-distribution? Do they exist in closed form? A quick Google search didn't give me any results.</p>
<p>Today I am interested in the univariate case, but probably I will have to extend the model to multiple dimensions.</p>
<p>EDIT: I am actu... | 49,740 |
<p>Let's say you have a jointly gaussian vector random variable $\mathbf{x}$, with mean $\mathbf{M}$ and covariance $\mathbf{S}$. I now transform each scalar element of $\mathbf{x}$ , say $x_j$, with a sigmoid:</p>
<p>$$y_j = 1/(1+\exp(-x_j))$$</p>
<p>I am interested in the expectation between two variables $y_j$ an... | 31,656 |
<p>I am quite new to <code>lmer</code> and quite confused about how to select the random effects part of the model.</p>
<p>The data I am working on is divided into dependent and independent variables. Each variable has two grouping factors. 1). sampling time (sample 1:7) and sampling column (1:24, where 1:3, 4:6 and s... | 70,602 |
<p>I conducted a survey, in which participants ranked themselves depending on how often they did something and how good they were at doing that thing. The input were integer values on the survey and <em>deliberately</em> did not have a maximum (or minimum) range. </p>
<p>Now I'm running some analysis and calculations ... | 456 |
<p>To understand my question, can anyone to evaluate if the statistical analysis in the below research (from the 2011 year) was performed correctly? I must to analyze a similar research and I am interested in the correct method. Initially I supposed that in this kind of research must be used the Wilcoxon test, but now... | 2,553 |
<p>I have trained a model that predicts a multinomial output. Would anyone know how the accuracy can be measured. </p>
<p>The target takes on the following values: "Yellow","Red,"Green","Blue".</p>
<p>I know that for binomial targets, ROC/AUC provide a good solution. But I haven't found anything for my problem. Would... | 70,603 |
<p>I am new in statistics so sorry about my elementary question. I have a data set and simple linear regression equation calculated from this data:</p>
<pre><code>f(x) = ax + b
</code></pre>
<p>I would like to know if I can (and if so how) use slope (<code>a</code>) from this linear regression to determine strength o... | 70,604 |
<p>I have some data points for which I would like to show the density using Python, but the package SciPy is not working for Python 3.3. </p>
<p>I am looking for a solution to be able to plot some data in the shape of a normal density. I do not know how to get the nice drawing. When I sort the data points, it would be... | 31,660 |
<p>I have sample data that maps intervals to a number:</p>
<pre><code>[3,7] => 1
[6,8] => 2
[6,13] => 3
[7,10] => 3
[10,13] => 4
</code></pre>
<p>The dependent variable's values will generally increase as the intervals' values increase in a nonlinear fashion (and they're not part of a finite set, so cl... | 70,605 |
<p>I have used <code>lme</code> and <code>ezAnova</code> to analyse data from a 2$\times$3 repeated-measures experiment. Theoretically those are two different ways to perform the same analysis. However, the resulting $F$-statisics and DF differ and I am lost in why.</p>
<p>Here is the exact data and output:
I have a d... | 70,606 |
<p>I'm using the HoltWinters function in R and I'm trying to understand what the "coefficients" represent in the object that is returned by that function. They don't seem to match in any obvious way the values returned when you look at the $</p> | 70,607 |
<p>Using R, what function(s) would I use to obtain the following probabilities? </p>
<ul>
<li>Roll at least one 1 when rolling 2 six-sided dice (2d6) = 11/36</li>
<li>Roll at least one 1 when rolling 3 six-sided dice (3d6) = 91/216</li>
<li>Roll at least one 1 when rolling 1d4, 1d6, 1d8, and 1d8 = 801/1536</li>
</ul>
... | 31,662 |
<p>I'm running a predictive model to predict the probability of winning a certain item based on the price that I bid (other factors also). After running the model (ols) in R, I wanted to account for all the variables in my model and develop a graph highlighting the 'predicted probabilities' regarding the primary variab... | 134 |
<p>Let's say, I have an intelligence test made of 60 questions (items) which produces results for two intelligence constructs on a 0-100 scale (for instance crystallised and fluid intelligence).</p>
<p>I only have respondent's final scores on the two constructs. So, I don't have answers to single items.
In such a scen... | 31,663 |
<p>I'm doing timings of an application which speeds up as we add threads. However, the times vary on repeated runs. What I'd like to have is a speedup chart which shows how many times faster than the baseline the application is, for each thread count I test on. </p>
<p>The data I was planning on gathering was 5-10 ru... | 42,203 |
<p>I have a list of 300 $p$ values selected from all $p$ values obtained in multiple testing such that $p<.05$. I do not know the values of $p>.05$ or their number. The $p$ values are not corrected for multiple testing, and I would like to do so for the 300 raw $p$ values that I have.</p>
<p>Is it OK to apply th... | 31,666 |
<p>I am studying Larry Wasserman's <a href="http://www.stat.cmu.edu/~larry/=stat705/" rel="nofollow">lecture notes</a> on Statistics which uses Casella and Berger as its primary text. I am working through his <a href="http://www.stat.cmu.edu/~larry/=stat705/Lecture2.pdf" rel="nofollow">lecture notes set 2</a> and got s... | 38,215 |
<p>I have some data that I know are related but I can't seem to find the exact relationship. Was hoping someone could help find it. Left column data is related to the right column.</p>
<pre><code>1160786507 E02K
1432646245 Udre
1211119187 H06S
1214345830 HARF
1211117653 H00U
1429221446 U0... | 70,608 |
<p>I'm currently trying to analyze Tweets and classify them as either positive, negative, or neutral using the NLTK library in Python.</p>
<p>I can see that there's potential in the approach that I'm taking, however, I'm having trouble with my feature selection process. </p>
<p>Indeed, input from Twitter isn't exactl... | 31,669 |
<p>I'm testing for difference in a continuous outcome under three different conditions. </p>
<p>Under condition A I take a measurement of the outcome. I do this twice for the same sample. Example values could be 2.2, 2.1. These are "technical" replicates that come from the same biological source</p>
<p>I do the same ... | 70,609 |
<p>Most coefficients (e.g., odd ratios, mean differences, etc.) can be converted into a (Pearson-like) correlation coefficient.</p>
<p>Q: Is there a conversion from probit coefficient --> correlation coefficient?</p> | 70,610 |
<p>I'm trying to reproduce an existing prediction algorithm, handed down by a retired researcher. The first step is to fit some observed data to a Weibull distribution, to obtain a shape and scale which will be used for predicting future values. I'm using R to do this. Here's an example of my code:</p>
<pre><code>x<... | 70,611 |
<p>I am referring to G.S. Maddala: Limited Dependent and Qualitative Variables in Econometrics, pages 257-258. I add the relevant screenshots here:</p>
<p><img src="http://i.stack.imgur.com/fuVav.png" alt="p1">
<img src="http://i.stack.imgur.com/M8F6e.png" alt="p2"></p>
<p>My question is, why is $\sigma_{2u}>\sigm... | 6,051 |
<p>The second peak of the <code>density plot</code> is large in this example. Why does the rug representation of the data--which seems to show few high values--not appear to match the much higher density estimated there?</p>
<p>How can one make rug plots less misleading?</p>
<p><img src="http://i.stack.imgur.com/Zj9... | 70,612 |
<p>How much validity is there in doing external hand hygiene observations in a hospital where another facility observes for a total of 6 hrs. twice a year and reports that data out, when the observed facility already has their own internal hand hygiene observers to obtain there own data monthly?</p> | 70,613 |
<p>Can anybody please explain or point to an online resource that explains the Fourier phase randomization technique? I encountered it in the context of comparing the cross-correlation of two signals before and after Fourier phase randomization. What does it mean when the cross-correlation disappears after Fourier phas... | 31,676 |
<p>My understanding is that with cross validation and model selection we try to address two things:</p>
<p><strong>P1</strong>. Estimate the expected loss on the population when training with our sample</p>
<p><strong>P2</strong>. Measure and report our uncertainty of this estimation (variance, confidence intervals, ... | 70,614 |
<p>I need to optimize parameters of a Gaussian shaped function to best fit my data points using maximum likelihood.</p>
<p>I first make an initial estimate for the parameters (mu, sigma and peak) and apply a gradient descent (fmincon in Matlab) algorithm to optimize these parameters. </p>
<p>The cost function is the ... | 31,678 |
<p>I have three variables, A, B, and C. It seems obvious that if X = A-B and Y = C-B that there should be a correlation between X and Y. When I've done this in matlab with random numbers, this seems to be the case with a mean r of about 0.5. The fact that there is a correlation makes intuitive since because X and Y ... | 268 |
<p>Say there are $m+n$ elements split into two groups ($m$ and $n$). The variance of first group is $\sigma_m^2$ and variance of second group is $\sigma^2_n$.
The elements themselves are assumed to be unknown but I know the means $\mu_m$, $\mu_n$ and $\mu_{(m+n)}$. The variance doesn't have to be unbiased so denominat... | 70,615 |
<p>I have a data set where different measures are taken repeatedly (3) times for multiple samples, like so:</p>
<pre><code> A B C
X ...
Y ...
</code></pre>
<p>So, for people X, Y, etc I have measures A, B, C and so on. Each of A, B, C are measured 3 times for each sample. That is, for each person, I have 3 meas... | 31,680 |
<p>Long post. Question at the bottom.</p>
<p>My data look likes this:</p>
<p><img src="http://i.stack.imgur.com/BSKqG.png" alt="enter image description here"></p>
<p>It consists of the test set accuracies of a series of 50 models formed on training sets. </p>
<p>Using random sampling of the raw observations, I cre... | 31,681 |
<p>I would appreciate another opinion on this simulation approach to estimating power for a within-subjects (or repeated-measures) ANOVA; in this case a 2x2 factorial design. In other words, is there anything WRONG with this method that I've missed? The code below is R.</p>
<hr>
<pre><code>library(ez)
nsub = 30
ncon... | 70,616 |
<p>I've just come across <a href="http://blog.plot.ly/post/68951620673/why-graph-anscombes-quartet">Anscombe's quartet</a> (four datasets that have almost indistinguishable descriptive statistics but look very different when plotted) and I am curious if there are other more or less well-known datasets that have been cr... | 31,682 |
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