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# Cross Validated : Recent Questions and Answers

## Logistic regression model predicts only one outcome, producing a high specificity but very low sensitivity. How do I improve the model?

I'm designing a logistic regression model to predict hospital mortality. Why? To identify 'adjusted' odds ratios for a variable of interest on mortality. Methods: - set up using a training...

## Why does the Lasso provide Variable Selection?

I've been reading Elements of Statistical Learning, and I would like to know why the Lasso provides variable selection and ridge regression doesn't. Both methods minimize the residual sum...

Asked on 11/29/2021 by Zhi Zhao

## Why do increasing regularization weights make objective function not monotonically decrease?

I run modified non-negative matrix factorization (NMF) and tune the regularization weight from 1e5 to 1e13. The table below shows errors from calculating cost function for 25 iterations of...

## Do we need to demean and standardize all variables in a model?

I am analyzing a panel data set with 55 countries. The coefficient of my variable of interest is not naturally interpret able. Hence, I thought of demeaning and standardizing my...

Asked on 11/29/2021 by Ama Perera

## linear causal model

Currently I’m focused on linear causal model expressed as a structural equation like this: $y = beta_1 x_1 + beta_2 x_2 + … + beta_k x_k + u$ ...

## What is the point of test set in ML?

The typical ML process consist of 3 sets:Training, Dev, Test set. But the actual training and tuning only happens in the training and dev sets. And the final result...

Asked on 11/29/2021 by Lelouche Lamperouge

## Proof that Cov(W+Y, Y-V) = 0 given that W, Y, and V are uncorrelated but not independent

$newcommand{Cov}{operatorname{Cov}}$I'm trying to prove the following statement: $Cov(W+Y , Y-V) = 0$, given the following constraints:$W$,$Y$, and $V$ are Uncorrelated but not independent$E(W)=E(Y)=E(V)=mu$...

## Can linear and logistic regression coefficients be combined using an inverse variance weighted average?

Suppose I have coefficients from several studies, some are linear regressions and some are logistic regressions. They measure the same construct, but because of the nature of the experiments (i.e.,...

## How to construct one sided CI for Superiority Randomized Controlled Trial?

I am a Ph.D. student conducting a superiority randomized controlled trial to test the effect of text message reminders on the timeliness of child vaccination. I have considered one-sided alpha...

## Working out expected steps of absorbent Markov Chain with more than one sink

So I've seen answers regarding the relative probabilities of winning given that two people are tossing coins until one wins, with one person winning with HHT and the other with...