Cross Validated Weekly Newsletter - Monday, September 28, 2015

Top new questions this week: Will the fact that my Italian son is going to attend a primary school change the expected number of Italian children to be present in his class? This is a question stemming from a real-life situation, for which I have been genuinely puzzled about its answer. My son is due to start primary school in London. As we are Italian, I was curious to ... probability self-study average   asked by user90213 27 votes answered by Erik 22 votes Why is there no closed form lasso solution? The lasso problem $$\beta^{\text{lasso}}= \operatorname*{argmin}_\beta \| y-X\beta\|^2_2 + \alpha \| \beta\|_1$$ has the closed form solution: $$ \beta_j^{\text{lasso}}= ... regression lasso regularization   asked by Norbert 17 votes answered by Guðmundur Einarsson 11 votes How to predict outcome with only positive cases as training? Computational biologist with limited machine learning experience looking for advice here. To make things easier, let's say I'm working on the classic example of spam/not-spam emails. I have a set of ... machine-learning predictive-models unsupervised-learning supervised-learning semi-supervised   asked by enricoferrero 15 votes answered by Marc Claesen 14 votes Textbooks/readings on what to do when you can't create an ideal experiment? My statistical training is rooted in mathematical statistics, and taking these methods classes in my M.S. are a bit of a shock at the moment; it is currently difficult for me to be able to understand ... references experiment-design   asked by Clarinetist 11 votes answered by forecaster 10 votes What are the merits of different approaches to detecting collinearity? I want to detect whether collinearity is a problem in my OLS regression. I understand that variance inflation factors and the condition index are two commonly used measures, but am finding it ... multiple-regression references least-squares multicollinearity vif   asked by kyrenia 10 votes answered by Stephan Kolassa 9 votes An example of a consistent and biased estimator? Really stumped on this one. I would really like an example or situation where a time series regression has an estimator would be both consistent and biased. time-series econometrics bias consistency   asked by Jimmy Wiggles 8 votes answered by JohnK 18 votes What does the formula y ~ x + 0 in R actually calculate? What is the statistical difference between doing a linear regression in R with the formula set to y ~ x + 0 instead of y ~ x? How do I interpret those two different results? multiple-regression generalized-linear-model intercept   asked by JimBoy 7 votes answered by gung 9 votes Greatest hits from previous weeks: Is chi-squared always a one-sided test? A published article (pdf) contains these 2 sentences: Moreover, misreporting may be caused by the application of incorrect rules or by a lack of knowledge of the statistical test. For example, the ... hypothesis-testing chi-squared   asked by Joel W. 30 votes answered by gung 33 votes Bottom to top explanation of the Mahalanobis distance? I'm studying pattern recognition and statistics and almost every book I open on the subject I bump into the concept of Mahalanobis distance. The books give sort of intuitive explanations, but still ... normal-distribution mathematical-statistics distance pattern-recognition intuition   asked by jjepsuomi 53 votes answered by whuber 84 votes Can you answer these? What to do when LDA over-fits I'm looking for guidance on ways to improve my test set prediction accuracy when using Linear Discriminant Analysis (LDA). I have a matrix of ~10K rows x 24K columns. Of the 24K features, 4 represent ... time-series machine-learning predictive-models   asked by Eric C. 2 votes What are the computational limitations of neural networks in FEM? I started to think the computational power of neural networks and why they have not been applied widely in non-adaptive finite element methods (FEM). In industry, I have noticed that most systems use ... neural-networks   asked by Masi 2 votes How can I understand and visualize the distribution implied by a series of sieves? I have data that defines a number of grit sizes in terms of sieve tests. I wish to understand and visualize the implied particle size distribution of these grits as well as possible. The data looks ... distributions data-visualization   asked by Mr.Wizard 3 votes

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