question stringlengths 37 38.8k | group_id int64 0 74.5k |
|---|---|
<p>I need to compute quartiles (Q1,median and Q3) in real-time on a large set of data without storing the observations. I first tried the P square algorithm (Jain/Chlamtac) but I was no satisfied with it (a bit too much cpu use and not convinced by the precision at least on my dataset).</p>
<p>I use now the FAME... | 70,791 |
<p>If one is testing assumption of homoscedasticity, parametric (Bartlett Test of Homogeneity of Variances, <code>bartlett.test</code>) and non-parametric (Figner-Killeen Test of Homogeneity of Variances, <code>fligner.test</code>) tests are available. How to tell which kind to use? Should this depend on e.g. normality... | 70,792 |
<p>I have two sets of results from an experiment that produces distributions with extremely heavily stacked sides and mostly uniform elsewhere. The aim of my analysis is to answer a the question roughly put like this : "With what degree of certainty can I say that the difference between Results A and Results B are not ... | 70,793 |
<p>I am applying a clustering algorithm (K-means) to a huge set of high dimensional data points (SIFT descriptors).
The algorithm is not deterministic and its results depend on the initialization of the centroids.</p>
<p>I am measuring the final performance of my system with Average Precision, and I am noticing that t... | 30,439 |
<p>I am trying to understand the level of a test better and was wondering if the level of a hypothesis is essentially equal to the probability that the null hypothesis is true. I have been trying to think of a counter example but haven't been able to confirm nor deny this association. Could anyone be kind enough to she... | 49,294 |
<p>I am working in a BPO with lots of projects coming in. I would like to know whether is there any book (statistical) through which I can tell whether the incoming project is viable and the company should take it.</p> | 70,794 |
<p>I'm trying to do rolling regression for the nonlinear equation (exponential). My functional form (stata form) for nonlinear equation is:</p>
<p><code>nl(weeklygrowth=({alpha1}+{alpha2}*day+{alpha3}*day2+{alpha4}*day3+{alpha5}*day4{a1}*m1+ {a2}*m2+ {a3}*m3+{a4}*m4+{a5}*m5+{a6}*m6+{a7}*m7+{a8}*m8+{a9}*m9+{a10}*m10+{a... | 70,795 |
<p>Suppose a theory claims that a random variable $R$ (of unknown distribution $F$) must satisfy a certian upper bound $R < c$ (where $c$ is known constant). Suppose I perform a set of measurements $X_1,...,X_n$ which are iid~$F$, but because of errors, I observe $X_1+E_1,...,X_n+E_n$ where $E_1,...,E_n$ are indepen... | 70,796 |
<p>Assume that I have a discrete set $L$ and a transformation $\phi: L \rightarrow [0,1]$ that normalizes set $L$ such that now values belonging $L$ are uniformly distributed among the unit interval.</p>
<p>How do I mathematically state that $\phi(L)$ adheres to uniform distribution?</p> | 27,044 |
<p>How can I define correlation between two set x and y:</p>
<p>{$(x_1,y_1),(x_2,y_2),(x_3,y_3),...(x_n,y_n)$}</p>
<p>Is this definition correct:</p>
<p>Correlation=$\frac{\sum\limits_{i=1}^{n}(Covarianc(x_i,y_i))}{\sqrt{\sum\limits_{i=1}^{n}(Variance(x_i)Variance(y_i))}}$</p> | 4,133 |
<p>I hope this is the right section for this kind of questions.</p>
<p>I am trying to simulate, with MATLAB, a diffusion model starting from a Random Walk.
I am using a Random Walk with information increment X normally distributed ($\mu, \sigma$ ).
I also have a boundary $\alpha $, and $\alpha > \mu$. The startin... | 31,911 |
<p>A colleague has collected data on plant root gene expression. Gene expression is expected to change over time, and be dependent upon the environment that each plant is grown in (i.e fertilizer mix). Measuring gene expression kills the plant, so each plant can only be sampled once. My colleague has two groups (hig... | 70,797 |
<p>I'm trying to come up with a metric for measuring non-uniformity of a distribution for an experiment I'm running. I have a random variable that should be uniformly distributed in most cases, and I'd like to be able to identify (and possibly measure the degree of) examples of data sets where the variable is not unif... | 70,798 |
<p>I think I have already answered my question, but am not completely sure and would like some input. Please feel free to correct my terminology or misconceptions, I learned stats by osmosis rather than formal courses so my knowledge is somewhat patchy and I often seem to use the wrong terminology.</p>
<p>We need to p... | 70,799 |
<p>I saw a comment by mpiktas that <a href="http://stats.stackexchange.com/questions/10856/what-is-the-distribution-of-the-difference-of-two-t-distributions">"The sum of two independent t-distributed random variables is not t-distributed"</a>. Is it then of any known distribution?</p>
<p>Actually, I am using piece-wis... | 31,915 |
<p>I am studying LDA, but have very weak statistical knowledge. I have a question regarding Gibbs sampling, one of the methods for inferring the distribution of topics and words-topic given a document, which basically iterates and computes the probability of words from being assigned to each topic after removing the sp... | 42,529 |
<p>For a particular application I'm trying to specify a model for the level of contact between two communities, similar to modeling migration. I have no data on contact rates between communities, so there's no parameter estimation here - I'm just trying to posit a reasonable model. </p>
<p>The information I have at ha... | 70,800 |
<p>I want to fit lognormal distribution to my data, using python <code>scipy.stats.lognormal.fit</code>. According to the <a href="http://docs.scipy.org/doc/scipy-0.7.x/reference/generated/scipy.stats.lognorm.html" rel="nofollow">manual</a>, <code>fit</code> returns <em>shape, loc, scale</em> parameters. But, lognormal... | 70,801 |
<p>Suppose one has 2 placebo-controlled clinical drug trials (drug X vs placebo; and drug Y vs placebo).</p>
<p>And suppose one creates a Kaplan-Meier plot for time to some event (eg, disease progression) for drug X vs placebo, and one creates another similar K-M plot for drug Y vs placebo.</p>
<p>Would it then be va... | 31,918 |
<p>If A, B and C are independent events with $P(A) = 0.3$, $P(B) = 0.2$ and $P(C) = 0.4$,
compute $P(A \cap B|B \cup C)$.</p>
<p>$$P(A \cap B|B \cup C) = P((A \cap B) \cap (B \cup C))/P(B \cup C) = P(A \cap B)/P(B \cup C)$$</p>
<p>I can't really understand how the statement in numerator $P((A \cap B) \cap (B \cup C))... | 70,802 |
<p>If two variables are related in this way,</p>
<p>$y=a+bx$</p>
<p>How to prove that these variables are perfectly correlated(correlation coefficient of 1) using covariance?</p>
<p>Need some guidance to start..</p> | 70,803 |
<p>Assume we now have a sequence of numbers $a_{i}$, $1\le i\le n$. We random pick up a sample of size $m,1<m<n$. What is the expectation value for the average of the sample? Is there any quick way to find a rough bound on this?</p> | 70,804 |
<p>I am trying to derive the ordinary kriging equations when I want to estimate the underlying value at $T(x_0)$ from the noisy observations at its neighbors $Z(x_1),....Z(x_n)$.</p>
<p>$Z(x_0) = T(x_0) + \epsilon$ where $\epsilon$ ~ $N(0,1)$</p>
<p>I was following the wikipedia article <a href="http://en.wikipedia.o... | 70,805 |
<p>I'm reading <em>"The Role of Chess in Artificial Intelligence Research"</em> (<a href="http://www.ijcai.org/Past%20Proceedings/IJCAI-91-VOL1/PDF/084.pdf" rel="nofollow">pdf</a>) and interestingly, it says:</p>
<blockquote>
<p>Experience [...] suggests that inputs from chess experts, while generally useful, canno... | 70,806 |
<p>In the mid 1960s, researchers have famously referred to chess as the "drosophila of AI": like the fruit fly, the game of chess was accessible and relatively simple problem to experiment on, which yet produced important knowledge more complex problems.</p>
<p>Now, people seem to say "chess is just a search problem" ... | 70,807 |
<p>I have access to a very large dataset. The data is from <a href="http://en.wikipedia.org/wiki/Magnetoencephalography">MEG</a> recordings of people listening to musical excerpts, from one of four genres. The data is as follows:</p>
<ul>
<li>6 Subjects</li>
<li>3 Experimental repetitions (epochs)</li>
<li>120 Trials ... | 70,808 |
<p>For a while, it seemed like <a href="http://en.wikipedia.org/wiki/Fisher_kernel">Fisher Kernels</a> might become popular, as they seemed to be a way to construct kernels from probabilistic models. However, I've rarely seen them used in practice, and I have it on good authority that they tend not to work very well. T... | 42,540 |
<p>I have some data I want to analyze, for which I was curious whether one or more conditions lead to measurements significantly different from the rest. I started out by making a table of t-test p-values comparing the condition which looked different in my graphic plot with all the others.</p>
<p>I was told by people... | 31,933 |
<p>I am using the gbm package to fit a binary variable using several attributes, some numeric and some categorical. Since the output varible was defined as factor I initially did</p>
<pre><code>boostFit <- gbm(output ~ ., data = df3[folds != k, ],
n.trees = 1000, shrinkage = 0.01,
... | 70,809 |
<p>I would like to regress total energy expenditure on age, gender, height and weight.But how do I check whether this relationship is linear?</p> | 70,810 |
<p>I have been searching for several days for a method that fits this description, though cannot find one. I'm pretty sure it must exist. </p>
<p>The problem (short version):</p>
<p>I'd like to run something like a CART, though instead of making splits to improve information/purity, it would make splits to maximise t... | 31,934 |
<p>For a single ROC curve (with relevant AUC score), how can you calculate the confidence interval? (The data used to generate this ROC/AUC is available)</p>
<p>Given my relatively limited background in this area, this would be a case of 'the easier, the better'.</p>
<p>PS: please also inform me of any conditions th... | 70,811 |
<p>I have tried reading up on different sources, but I am still not clear what test would be the appropriate in my case. There are three different questions I am asking about my dataset: </p>
<ol>
<li><p>The subjects are tested for infections from X at different times. I want to know if the proportions of positive ... | 70,812 |
<p>I am using a computer simulation to produce experimental results. The simulation has a pseudo-random element and so is ran multiple times in order to investigate general behaviour. </p>
<p>Are there any methods which look at the distribution of the samples taken and predict (with a given certainty) whether they ar... | 70,813 |
<p>I'm working my way through a simple dynamic pricing model, and I'm having trouble figuring out how to optimize what I'm working on.<br/>
I want to maximize $\Sigma_{t=1}^TR(D_t) - h_tI_t$
for the constraints:<br/>
$I_{t+1} = I_t - D_t$<br/>
$I_1=1500$<br/>
$I_t, D_t integers\ge 0$<br/>
where $R(D_t)$ is revenue as a... | 70,814 |
<p>I'd like to perform an ANOVA with a normally distributed response variables and several explanatory variables. Some of the explanatory variables are continuous and some are categorical (factor(..)).</p>
<pre><code>aov(a~numeric(b) + factor(c ) + numeric(d) + factor(e))
</code></pre>
<p>The residuals of this model ... | 31,937 |
<p>I want to test statistical methods for model selection in binary classification problems. In order to do so, I plan to generate data and then use some specific model (i.e. fix parameters for my model) to assign labels for each sample. Finally, I will try to retrieve the right parameters by choosing among several mod... | 70,815 |
<p>I am trying to fit my data to the one of the continuous PDF (I suggest it to be gamma- or lognormal-distributed). The data consists of about 6000 positive floats.
But the results of the Kolmogorov-Smirnov test completely refute my expectations providing the very low p-values. </p>
<p>Data empirical distribution</p>... | 70,816 |
<p>I read an interesting statement: running the same data through multiple tests no longer counts as multiple comparisons. </p>
<p>I am fairly confident this is incorrect if you are testing different hypotheses e.g. testing for hundreds of different lags on the same data will yield some false significant results (if y... | 70,817 |
<p>The <em><a href="http://en.wikipedia.org/wiki/Iris_flower_data_set">"Iris"</a></em> dataset is probably familiar to most people here - it's one of the canonical test data sets and a go-to example dataset for everything from data visualization to machine learning. For example, everyone in <a href="http://stats.stacke... | 30,451 |
<p>I calculated the quantiles for an Epanechnikov kernel which I'm using to estimate the density of a sample. What I need is to find the sample quantiles knowing that it is composed of many Epanechnikov kernels. Is there a way to calculate at wich data points the different quantiles are using the kernel inverse CDF for... | 42,558 |
<p>Consider the general regression model
$$Y=X\beta+\epsilon$$
where,</p>
<p>$Y$ is an $(n\times 1)$ vector of observations,</p>
<p>$X$ is an $(n\times p)$ matrix of known form,</p>
<p>$\beta$ is a $(p\times 1)$ vector of parameters,</p>
<p>$\epsilon$ is an $(n\times 1)$ vector of errors.</p>
<p>The fitted values... | 70,818 |
<p>as question, since we can do the conversion from odds ratio <code>(p1/q1)/(p2/q2)</code> to relative risk <code>(p1/(p1+q1))/(p2/(p2+q2))</code> fairly easily, I wonder if there is anything that I need to pay attention before doing this?</p>
<p>It is obvious that if I am doing a case-control study, I shouldn't do a... | 42,559 |
<p>I have serial hematological measurements data and I have plotted their means and SE in Stata. On the y-axis I have for example hemoglobin and time (visit days) on the x-axis hence I can visualize hemoglobin levels with time (whether it is decreasing or in increasing). The level decreases up to sometime and increases... | 42,561 |
<p>In the Albert book on Bayesian computation with R, exercise 4.8.5 (p.83), it is suggested to use</p>
<p>$$
p(a, b) \sim (a \times b)^{-2}
$$</p>
<p>as the non-informative prior for the Poisson/Gamma model:</p>
<p>$$
f(y\,|\, a,b) = \frac{\Gamma(y+a)}{\Gamma(a) \times y!}\frac{b^{a}}{(b+1)^{y+a}}
$$</p>
<p>It do... | 70,819 |
<p>I have a sample composed by 2500 count data values. I've plotted in R the corresponding histogram and ecdf. I've run the One-Sample Kolmogorov-Smirnov test to check if the distribution is either exponential or poisson, but I got negative results.</p>
<p>Is it possible that the One-Sample Kolmogorov-Smirnov test, it... | 49,373 |
<p>I am trying to implement and learn a Dirichlet Process to cluster my data (or as machine learning people speak, estimate the density). </p>
<p>I read a lot of paper in the topic and sort of got the idea. But I am still confused; here are a series of question,</p>
<p>1) What is the different between Chinese Restaur... | 31,952 |
<p>Suppose that we have different evidences $e_1, e_2, \ldots$, and we know the conditional probability of event $t$ over each of them, say $P(t|e_i)$.</p>
<p>Now I have a set of observed evidences $e_i$, and want to know the probability of $t$ happening. Does it make sense to use $P(t|e_1) + P(t|e_2)$? Or is there an... | 31,953 |
<p>Can I use some part of the real time dataset for getting an overview about the dataset before applying an algorithm? Can I use <code>ELKI</code> or <code>R</code> software for this?</p> | 70,820 |
<p>I am currently doing spectral analysis on a bivariate time series, and I have a little problem when trying to plot the phase :<img src="http://i.stack.imgur.com/HGZd3.png" alt="Cross-spectra"></p>
<p>When the phase is higher than pi, the value is taken modulo 2pi. The problem is not the plot in itself, but the way ... | 70,821 |
<p>I am using the glmnet package in R. When I set the alpha value = 0,
I would expect that no variables are selected. When I look at the coefficients some of them are set to zero.
What could be the explanation for this behaviour?</p> | 31,954 |
<p>I am trying to replicate the "C3 Contrast" (Output 66.3.7) at the bottom of:</p>
<p><a href="http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_phreg_sect048.htm" rel="nofollow">http://support.sas.com/documentation/cdl/en/statug/63962/HTML/default/viewer.htm#statug_phreg_sect048... | 70,822 |
<p>I have a covariance function $f(x)$, where $x = (x_1, x_2, x_3)$ is a point in three-dimensional space. I need to generate a Gaussian field with given covariance function on a 3D grid of points, that is very large (the storage of full covariance matrix is impossible, so a Cholesky decomposition is fail). What is the... | 70,823 |
<p>The statistical analysis of experimental data that I have to perform could be described as follows. Three drug treatments $D_1$, $D_2$ and $D_3$ were tested across three groups $G_1$, $G_2$ and $G_3$. For each group and treatment combination $D_i, G_k$ the data are exposure (no of patients being treated with drug) a... | 30,459 |
<p>I want to use the Local Outlier Factor (LOF) algorithm for outlier detection but it simply finds outliers on unlabed data as whole and you do not need to have a training and test set. However in my case I expect to get some knowledge from the training set and test this knowledge on test data (it seems like an ordina... | 31,961 |
<p>The title sums up my question, but for clarity consider the following simple example. Let $X_i \overset{iid}{\backsim} \mathcal{N}(0, 1)$, $i = 1, ..., n$. Define:
\begin{equation}
S_n = \frac{1}{n} \sum_{i=1}^n X_i
\end{equation}
and
\begin{equation}
T_n = \frac{1}{n} \sum_{i=1}^n (X_i^2 - 1)
\end{equation}
<strong... | 31,962 |
<p>I've been researching the use of Bayesian linear regression, but I've come to an example that I'm confused about.</p>
<p>Given the model:</p>
<p>$${\bf y} = {\bf \beta}{\bf X} + \bf{\epsilon} $$</p>
<p>Assuming that ${\bf \epsilon} \sim N(0, \phi I)$ and a $p(\beta, \phi) \propto \frac{1}{\phi}$,</p>
<p>How is $... | 42,581 |
<p>I have a series of discrete, purportedly random whole numbers like this:</p>
<pre>
v1 v2 v3 v4 v5 v6
42 23 10 07 01 35
05 02 26 25 49 18
35 18 43 29 26 28
36 59 26 15 34 35
</pre>
<p>I want to identify if there are any values that co-occcur (in a row) more frequently than one would expe... | 70,824 |
<p>Is it logical to name low correlated features as valuable and choosing the low corelated ones for classification? Or it depends on the algorithm used for the purpose? How do I need to interpret a correlation matrix,then?</p> | 42,582 |
<p>I am fitting a Case-Cohort Proportional Harzards (CCH) model using the Survival (version 2.37-4) package in R 2.15.3. Normally with a Cox Proportional Harzards (coxPH) model, I can use the survfit function to predict the probability of a new patient being survival free at a specific time point; however, there is no ... | 70,825 |
<p>I'm trying to analyse, whether the effect of answer correctness ($X$, binary) on confidence ratings ($Y$, continuous) in some psychological task is mediated by another rating ($M$, continuous). In order to do so I created two LMER models (I use LMER to account for random effect for stimuli and subjects), <code>Y~X</... | 70,826 |
<p>I checked all the books and on-line materials I could find for the proof, but found all of them have a derivation problem, which I cannot understand. To prove the least squares estimator is the BLUE for the linear model y = X*b + v, one assumes c = C*y is any linear unbiased estimator of b. Using the fact that c is ... | 70,827 |
<p>I'm confused about how to interpret coefficients in relation to the reference categories. I have two variables, A and M. A is a 3-level variable and M is a 4-level variable. The reference category for A is level 3, and the reference category for M is level 4. Can someone show me how to interpret the relationships to... | 6,125 |
<p>Let $X_i \sim^{iid} F$ for $i=1,...,n$, where $F$ is a continuous distribution.</p>
<p>I want to find the pdf for $X_{(1)},X_{(2)},..., X_{(r)}$, with $r\leq n$.</p>
<p>We know that $f_{X_{(1)},X_{(2)},..., X_{(n)}}=n!\prod^n_{i=1}f(x_{(i)})$, when $x_{(1)}\leq x_{(2)}\leq \cdots\leq x_{(n)}$; $f_{X_{(1)},X_{(2)},... | 70,828 |
<p>Why would a polynomial SVM have better performance than a linear SVM but the same performance as a radial SVM? </p> | 70,829 |
<p><code>ggplot2</code> seems to, by default, select very nice, comprehensible breaks for continuous data. I would like to plot the data according to one scale (logistic) by having the axis labels in an easier-to-explain scale (percentage). I can make this plot by selecting breaks on the one scale and assigning label... | 26,735 |
<p>When minimizing a function by general Metropolis-Hastings algorithms, the function is viewed as an unnormalized density of some distribution. </p>
<p>(1) As density functions are required to be nonnegative, I was wondering if there is some restriction on functions that can be minimized by Metropolis-Hastings algori... | 25 |
<p>I am having a little difficulty understanding my results - could someone help me understand how to interpret, and if my process is sensible? Here is an example of what I am doing</p>
<p>I am trying to determine if drug_a, which is a synthetic hormone_a has an affect on hormone_b. First, I have log-transformed the d... | 31,978 |
<p>this is my first question on this site, so please be patient with me. I am doing a random walk, where I build a timeseries curve. I do that a preset number of times ( let's say 100 times ). Now I was wondering what should I do with all the generated curves. Eventually I want to have 1 curve that is the best represen... | 70,830 |
<p>Say I have a set of sample points generated by a multivariate normal distribution D whose parameters I don't know.</p>
<p>I want to be able to measure the distance from an arbitrary point to the distribution D.</p>
<p>One way of doing this would be to get an estimate of the parameters of D, and use it to get the m... | 31,980 |
<p>this is our code with latent class model</p>
<pre><code>model { # Marginal tabulations of Latent Diagnosis against Observed Items
for (i in 1:n) { for (j in 1:K) { for (k in 1:2) {M1[j,k,i] <- equals(T[i],j)*equals(Y[i,1],k-1)}}}
for (j in 1:K) {for (k in 1:2) {Tab1[j,k] <- sum(M1[j,k,1:n])}}
for (i in 1:n)... | 70,831 |
<p>I have records of census data comprised of complex data types including distributions, such as these two fields from a record, both of which are distributions.</p>
<p>The first is an income distribution:</p>
<pre><code>No income: 1110.0
$1 to $9,999 or loss: 13840.0 ######
$10,000 to $14,999: 9490... | 70,832 |
<p>I am asking for a book reference to further my studies in machine learning with the R programming language. Feel free to reference multiple books that are just machine learning or just R programming. I understand some basic concepts, but I think I am having trouble applying my knowledge to get real results.</p>
<p>... | 31,983 |
<p>I have two independent Poisson processes $A$ and $B$ with arrival rates $\lambda_A$ and $\lambda_B$, respectively. Now, the expected time for the arrival of the next item for the merged process should be $\frac {1}{\lambda_A+\lambda_B}$.</p>
<p>Assuming $T_{A+B}$ to be the arrival time for the next item of the comb... | 70,833 |
<p>I want to compare 2 independent variables, but the problem is that the first variable is normally distributed, while the second variable is not. What is the appropriate test in this case? Can I use an independent-samples t-test or the nonparametric Mann-Whitney test?</p> | 70,834 |
<p>I want to write some MATLAB code for the bandit problem, but I don't know what the exact algorithm is for this problem.
Is the Epsilon-Greedy algorithm right?</p>
<p>I have 5 slot-machines. For example, I should play a lever 1000 times as a task, and then if the mean of one machine's rewards are maximum in comparis... | 70,835 |
<p>I am using a genetic algorithm to search a very complex hypothesis space. Now I want to estimate how much overfitting I can expect in the final resulting hypothesis. The final model will be used for predicting <code>N</code> output variables from <code>M</code> predictors.</p>
<p>One simple test I can do is to repl... | 46,577 |
<p>I am trying to understand the convolution part of convolutional neural networks. Looking at the following figure:</p>
<p><img src="http://i.stack.imgur.com/C6UTY.png" alt="enter image description here"></p>
<p>I have no problems understanding the first convolution layer where we have 4 different kernels (of size $... | 70,836 |
<p>How do you identify the class of an "anonymized attribute" in statistical analysis? (By "anonymized attribute" I mean that I do not know whether the attribute is continuous or categorical).</p>
<p>The attribute takes integer value. I would like to know whether the attribute is continuous or categorical (nominal or ... | 49,571 |
<p>In one of Fisher's classical paper [1] I stumbled over the following:</p>
<blockquote>
<p>If the frequency with which the variate $x$ falls into the range $dx$, be given by $$df = \frac{1}{\pi}\frac{dx}{1+(x-m)^2}$$ where $m$ is the unknown parameter representing the centre of the symmetrical frequency curve of $... | 70,837 |
<p>Pardon if this question is very basic, but I am not able to find any solution for my problem. I am trying to run a feature selection scheme on N features for my classification model, however I want one of these features to always appear in the model. Is there a way to run feature selection on the remaining N-1 varia... | 70,838 |
<p>I have seen two formulas without explanation online:</p>
<p>$$Z_{\beta} = t - Z_{\alpha}$$</p>
<p>and </p>
<p>$$Z_{\beta} = \frac{t - \text{EffectSize}}{\sqrt{1 + t^2 / (2 \text{df})}}$$</p>
<p>Of course the simplicity of the first formula is attractive, but I would be proceeding blindly. I do not have training... | 70,839 |
<p>My seminary paper deals with renewing tourist paths over a certain area. The workers doing the renewing must obviously go through all the paths at least once, but they are limited by a certain distance per day (e.g. 10 km). Where they begin or end is not relevant, they can use the car to get to the start just as wel... | 70,840 |
<p>Trying to: </p>
<ul>
<li>Plot survival function estimates (by arm or treatment) as well as associated point-wise confidence intervals based on the Exponential
distribution </li>
<li>Compare the Kaplan-Meier curves with the survival
curves from the exponential distribution model (for each arm/treatment)</li>
</ul>
... | 70,841 |
<p>Consider three time series x, v, w
The distribution of the values that x,v,w take are zero-mean Gaussian, stationary and independent of time (no temporal colleration) and of each other. We know the population variance of v and w but not x.</p>
<p>If we now consider the sample variances of the time series x+v and o... | 70,842 |
<p>I was conducting a 'recall of negative words' memory experiment with a two-way between-group ANOVA and got no significant main effects and no significant interaction! How can I go about explaining this in the Discussion section? Do I just state that it seems that my 2 between subjects factors have no influence over ... | 70,843 |
<p>I recently learned about the use of the Kernel trick, which maps data into higher dimensional spaces in an attempt to linearize the data in those dimensions. Are there any cases where I should avoid using this technique? Is it just a matter of finding the right kernel function?</p>
<p>For linear data this is of cou... | 32,003 |
<p>I attended a meeting of the <a href="http://www.spsp.org/">Society for Personality and Social Psychology</a> last week where I saw a talk by Uri Simonsohn with the premise that using an a priori power analysis to determine sample size was essentially useless because its results are so sensitive to assumptions.</p>
... | 70,844 |
<p>I have a dataset in which each row belongs to one of 8 categories. I'm running a logistic regrssion on it using R. I created dummy variables for each of these categories. In my logistic regression model I know one of these dummies need to be excluded to not fall for the dummy variable trap. However the model keeps k... | 70,845 |
<p>I've got some data about people in Bristol. I have about 75,000 records. Part of my dataset is each respondants age.</p>
<p>Aside from this, I have also downloaded census data for Bristol, which gives me the number of each in each age category i.e. 25000 people aged 1, 26000 people aged 2.... 916 people aged 100 et... | 32,004 |
<p>I just need a simple yes/no answer (hopefully yes) to confirm I haven't done something stupid here - I'm doing some data analysis and looking at the correlation of 2 variables X and Y over the past 6 years. My correlation over these 6 years comes out in MS Excel as 96% (that is, the usual definition of correlation a... | 148 |
<p>I have the population denominators for high (n = 28137) and low (n = 35167) deprivation areas in a city. I want to be able to compare the # of convenience stores per capita in high and low deprivation areas to see if there are more stores in one area versus another. There are n = 43 stores in high and n = 27 in low ... | 70,846 |
<p>I want to build feature vectors from data of my test set, which contains profiles of people.
I always want to compare two profiles to each other. </p>
<p>Thus my features are:<br>
- Same surname ∈ {undefined, yes, no}<br>
- age delta ∈ {undefined, x | x ∈ Z}<br>
- number of same interests ∈ N<br>
- genders ∈ {(mal... | 70,847 |
<p>Using R and ggplot, I would like to plot my output variable with one of my predictor variables adjusted for the other variables in the model. (I'm asking this question here, because I don't actually know if this is statistically a good idea! Please let me know if not!)</p>
<p>A model using dtcars data (nabbed from ... | 70,848 |
<p>My problem is as follows: I drop 40 equal balls at once from a certain point, a few meters over the floor. The balls roll, and comes to a rest. Using computer vision, I calculate the center of mass in the X-Y plane. I have both large and small balls, heavy and light, dropped in separate experiments. Each 40-ball dr... | 70,849 |
<p>I have a few questions about doing a linear mixed-effects model in R using the package lme4.
I have reaction time data with 3 fixed factors and random effects for subjects and items. I want to have a "maximal" random-effects structure as recommended by <a href="http://www.sciencedirect.com/science/article/pii/S07495... | 70,850 |
<p>Clinical trials are a field I am quite interested in and since I have trouble accepting that every clinical trial's data will follow a normal distribution with sufficient sample size I was curious as to whether there's any <strong>non-parametric test</strong> that's best suited for <strong>ratio independent two-samp... | 32,009 |
<p>I am trying to understand if newspaper ads have an effect on the number of visitors to a museum. There are two main newspaper the museum advertises on. The ads are in different size. What I've done is I have put in a column the visitors count for that month and then created a series of dummy variable, one for each a... | 32,012 |
<p>I've been working through the HW work in the online book <a href="http://a-little-book-of-r-for-time-series.readthedocs.org/en/latest/src/timeseries.html" rel="nofollow"><em>A little book of R for time series analysis</em></a>, and have started testing with some "live" customer data. I have a dataset that looks like... | 4,924 |
<p>Lets say I am regressing Y on X1 and X2, where X1 is a numeric variable and X2 is a factor with four levels (A:D). Is there any way to write the linear regression function <code>lm(Y ~ X1 + as.factor(X2))</code> so that I can choose a particular level of X2 -- say, B -- as the baseline? </p> | 32,014 |
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