The original ensemble method is Bayesian averaging, but more recent algorithms include error-correcting output coding, bagging, and boosting. So how do ensemble methods work and why are they superior to individual models? They average out biases: If you average a bunch of democratic-leaning polls and republican-leaning polls together, you will get an average something that isn't leaning either way. They reduce the variance: The aggregate opinion of a bunch of models is less noisy than the single opinion of one of the models. In finance, this is called diversification -- a mixed portfolio of many stocks will be much less variable than just one of the stocks alone.

Gradient descent is one of the most popular algorithms to perform optimization and by far the most common way to optimize neural networks. At the same time, every state-of-the-art Deep Learning library contains implementations of various algorithms to optimize gradient descent (e.g. These algorithms, however, are often used as black-box optimizers, as practical explanations of their strengths and weaknesses are hard to come by. This blog post aims at providing you with intuitions towards the behaviour of different algorithms for optimizing gradient descent that will help you put them to use. We are first going to look at the different variants of gradient descent.

As Google learned, predicting the spread of influenza, even with mountains of data, is notoriously difficult. Nonetheless, bioinformatician and R user Shirin Glander has created a two-part tutorial about predicting flu deaths with R (part 2 here). The analysis is based on just 136 cases of influenza A H7N9 in China in 2013 (data provided in the outbreaks package) so the intent was not to create a generally predictive model, but by providing all of the R code and graphics Shirin has created a useful example of real-word predictive modeling with R. The tutorial covers loading and cleaning the data (including a nice example of using the mice package to impute missing values) and begins with some exploratory data visualizations. I was particularly impressed by the use of density charts (using the stat_density2d ggplot2 aesthetic) to highlight differences in the scatterplots of flu cases ending in death and recovery. Decision trees (implemented using rpart and visualized using fancyRpartPlot from the rattle package) Random Forests (using caret's "rf" training method) Elastic-Net Regularized Generalized Linear Models (using caret's "glmnet" training method) K-nearest neighbors clustering (using caret's "kknn" training method) Penalized Discriminant Analysis (using caret's "pda" training method) and in Part 2, Extreme gradient boosting using the xgboost package and various preprocessing techniques from the caret package Due to the limited data size, there's not too much difference between the models: in each case, 13-15 of the 23 cases were classified correctly.

From the text mining literature, it appears that practitioners tend to utilize Cosine Distance to compare 2 documents. They have used it with great success. From our previous blog, we also used Cosine Distance and we also found it extremely good and helping us, and our clustering method, get an insight in the UK Exit Referendum. In here, we decided to change our initial conditions and see if we get different outcomes,i.e. We decided to try 4 others distances: Jaccard, Matching, Rogers Tanimoto and Euclidean.

Imagine I show you a book review, on amazon.com, Imagine I hide the number of stars, – all you get to see is the number of stars. And now I'm asking you, that review, is it good or bad? Well, it should be easy, for humans (although depending on the input there can be lots of disagreement between humans, too.) But if you want to do it automatically, it turns out to be surprisingly difficult.

What is normal for a machine (or the System under observation) is environment-dependent and ever-changing in real life!

What will be the impact of machine learning on economics? NEW YORK, NY - MAY 05: Susan Athey speaks at TechCrunch Disrupt NY 2014 - Day 1 on May 5, 2014 in New York City. The short answer is that I think it will have an enormous impact; in the early days, as used "off the shelf," but in the longer run econometricians will modify the methods and tailor them so that they meet the needs of social scientists primarily interested in conducting inference about causal effects and estimating the impact of counterfactual policies (that is, things that haven't been tried yet, or what would have happened if a different policy had been used). Examples of questions economists often study are things like the effects of changing prices, or introducing price discrimination, or changing the minimum wage, or evaluating advertising effectiveness. We want to estimate what would happen in the event of a change, or what would have happened if the change hadn't taken place.

Hi, when evaluating predictions, look at the initial breakdown in the data, because while you can get a good overall hit rate (i use 80% as a simple rule of thumb), looking at the data, what was your sensitivity and specificity. In other words, does your model classify both sets of conditions (outcome a and outcome b) you are modelling well? Having a high percentage in one group, and getting them classified correctly can really make your overall hit rate misleading. I would chek your residuals (the difference between your expected as a probability) and the observed, and see which cases you are misclassifying, and which ones you are misclassifying really badly,and perhaps then try and profile them. Also, remember that statistical significance can be boosted by sample size (power), and if you have a lot of cases, your predictors can be significanct.

I hope you enjoy them, and it would be great if you would leave brief reviews of these books in the comments below – I'm sure all the authors would appreciate your comments and shares. About the Author Lee Baker is an award-winning software creator with a passion for turning data into a story. A proud Yorkshireman, he now lives by the sparkling shores of the East Coast of Scotland. Physicist, statistician and programmer, child of the flower-power psychedelic '60s, it's amazing he turned out so normal! Turning his back on a promising academic career to do something more satisfying, as the CEO and co-founder of Chi-Squared Innovations he now works double the hours for half the pay and 10 times the stress - but 100 times the fun! He also wanted to be rich, famous and good looking.

Deep nonlinear models pose a challenge for fitting parameters due to lack of knowledge of the hidden layer and the potentially non-affine relation of the initial and observed layers. In the present work we investigate the use of information theoretic measures such as mutual information and Kullback-Leibler (KL) divergence as objective functions for fitting such models without knowledge of the hidden layer. We investigate one model as a proof of concept and one application of cogntive performance. We further investigate the use of optimizers with these methods. Mutual information is largely successful as an objective, depending on the parameters. KL divergence is found to be similarly succesful, given some knowledge of the statistics of the hidden layer.