big data - Eran Raviv

AI models are NOT biased

Blog, Statistics and EconometricsPosted on 06/11/2024

The issue of bias in AI has become a focal point in recent discussions, both in the academia and amongst practitioners and policymakers. I observe a lot of confusion and diffusion in those discussions. At the risk of seeming patronizing, my advice is to engage only with the understanding of the specific jargon which is used, and particularly how it’s used in this context. Misunderstandings create confusion and blur the path forward.

Here is a negative, yet typical example:

In artificial intelligence (AI)-based predictive models, bias – defined as unfair systematic error – is a growing source of concern¹.

This post tries to direct those important discussions to the right avenues, providing some clarifications, examples for common pitfalls, and some qualified advice from experts in the field on how to approach this topic. If nothing else, I hope you find this piece thought-provoking.

Matrix Multiplication as a Linear Transformation

Blog, Statistics and EconometricsPosted on 01/17/2024

AI algorithms are in the air. The success of those algorithms is largely attributed to dimension expansions, which makes it important for us to consider that aspect.

Matrix multiplication can be beneficially perceived as a way to expand the dimension. We begin with a brief discussion on PCA. Since PCA is predominantly used for reducing dimensions, and since you are familiar with PCA already, it serves as a good springboard by way of a contrasting example for dimension expansion. Afterwards we show some basic algebra via code, and conclude with a citation that provides the intuition for the reason dimension expansion is so essential.

Randomized Matrix Multiplication

Blog, Finance and Trading, Statistics and EconometricsPosted on 12/14/2023

Matrix multiplication is a fundamental computation in modern statistics. It’s at the heart of all concurrent serious AI applications. The size of the matrices nowadays is gigantic. On a good system it takes around 30 seconds to estimate the covariance of a data matrix with dimensions $X_{10000 \times 2500}$, a small data today’s standards mind you. Need to do it 10000 times? wait for roughly 80 hours. Have larger data? running time grows exponentially. Want a more complex operation than covariance estimate? forget it, or get ready to dig deep into your pockets.

We, mere minions who are unable to splurge thousands of dollars for high-end G/TPUs, are left unable to work with large matrices due to the massive computational requirements needed; because who wants to wait few weeks to discover their bug.

This post offers a solution by way of approximation, using randomization. I start with the idea, followed by a short proof, and conclude with some code and few run-time results.

Random forest importance measures are NOT important

Blog, Statistics and EconometricsPosted on 05/16/2021

Random Forests (RF from here onwards) is a widely used pure-prediction algorithm. This post assumes good familiarity with RF. If you are not familiar with this algorithm, stop here and see the first reference below for an easy tutorial. If you used RF before and you are familiar with it, then you probably encountered those “importance of the variables” plots. We start with a brief explanation of those plots, and the concept of importance scores calculation. Main takeaway from the post: don’t use those importance scores plots, because they are simply misleading. Those importance plots are simply a wrong turn taken by our human tendency to look for reason, whether it’s there or it’s not there.

Why complex models are data-hungry?

Blog, Statistics and EconometricsPosted on 11/19/2020

If you regularly read this blog then you know I am not one to jump on the “AI Bandwagon”, being quickly weary of anyone flashing the “It’s Artificial Intelligence” joker card. Don’t get me wrong, I understand it is a sexy term I, but to me it always feels a bit like a sales pitch.

If the machine does anything (artificially) intelligent it means that the model at the back is complex, and complex models need massive (massive I say) amounts of data. This is because of the infamous Curse of dimensionality.

I know it. You know it. Complex models need a lot of data. You have read this fact, even wrote it at some point. But why is it the case? “So we get a good estimate of the parameter, and a good forecast thereafter”, you reply. I accept. But.. what is it about simple models that they could suffice themselves with much less data compared to complex models? Why do I always recommend to start simple? and why the literature around shrinkage and overfitting is as prolific as it is?

Human significance, economic significance and statistical significance

Blog, Statistics and EconometricsPosted on 07/03/2016

We are now collecting a lot of data. This is a good thing in general. But data collection and data storage capabilities have evolved fast. Much faster than statistical methods to go along with those voluminous numbers. We are still using good ole fashioned Fisherian statistics. Back then, when you had not too many observations, statistical significance actually meant something.