Data Science Decoded

Data Science #32 - A Markovian Decision Process, Richard Bellman (1957)

We reviewed Richard Bellman’s “A Markovian Decision Process” (1957), which introduced a mathematical framework for sequential decision-making under uncertainty. By connecting recurrence relations to Markov processes, Bellman showed how current choices shape future outcomes and formalized the principle of optimality, laying the groundwork for dynamic programming and the Bellman equationThis paper is directly relevant to reinforcement learning and modern AI: it defines the structure of Markov Decision Processes (MDPs), which underpin algorithms like value iteration, policy iteration, and Q-learning. From robotics to large-scale systems like AlphaGo, nearly all of RL traces back to the foundations Bellman set in 1957

Data Science #31 - Correlation and causation (1921), Wright Sewall

On the 31st episode of the podcast, we add Liron to the team, we review a gem from 1921, where Sewall Wright introduced path analysis, mapping hypothesized causal arrows into simple diagrams and proving that any sample correlation can be written as the sum of products of “path coefficients.” By treating each arrow as a standardised regression weight, he showed how to split the variance of an outcome into direct, indirect, and joint pieces, then solve for unknown paths from an ordinary correlation matrix—turning the slogan “correlation ≠ causation” into a workable calculus for observational data.Wright’s algebra and diagrams became the blueprint for modern graphical causal models, structural‑equation modelling, and DAG‑based inference that power libraries such as DoWhy, Pyro and CausalNex. The same logic underlies feature‑importance decompositions, counterfactual A/B testing, fairness audits, and explainable‑AI tooling, making a century‑old livestock‑breeding study a foundation stone of present‑day data‑science and AI practice.

Data Science #30 - The Bootstrap Method (1977)

In the 30th episode we review the the bootstrap, method which was introduced by Bradley Efron in 1979, is a non-parametric resampling technique that approximates a statistic’s sampling distribution by repeatedly drawing with replacement from the observed data, allowing estimation of standard errors, confidence intervals, and bias without relying on strong distributional assumptions. Its ability to quantify uncertainty cheaply and flexibly underlies many staples of modern data science and AI, powering model evaluation and feature stability analysis, inspiring ensemble methods like bagging and random forests, and informing uncertainty calibration for deep-learning predictions—thereby making contemporary models more reliable and robust.Efron, B. "Bootstrap methods: Another look at the bootstrap." The Annals of Statistics 7 (1977): 1-26.

Data Science #29 - The Chi-square automatic interaction detection(CHAID) algorithm (1979)

In the 29th episode, we go over the 1979 paper by Gordon Vivian Kass that introduced the CHAID algorithm.CHAID (Chi-squared Automatic Interaction Detection) is a tree-based partitioning method introduced by G. V. Kass for exploring large categorical data sets by iteratively splitting records into mutually exclusive, exhaustive subsets based on the most statistically significant predictors rather than maximal explanatory power. Unlike its predecessor, AID, CHAID embeds each split in a chi-squared significance test (with Bonferroni‐corrected thresholds), allows multi-way divisions, and handles missing or “floating” categories gracefully.In practice, CHAID proceeds by merging predictor categories that are least distinguishable (stepwise grouping) and then testing whether any compound categories merit a further split, ensuring parsimonious, stable groupings without overfitting. Through its significance‐driven, multi-way splitting and built-in bias correction against predictors with many levels, CHAID yields intuitive decision trees that highlight the strongest associations in high-dimensional categorical data In modern data science, CHAID’s core ideas underpin contemporary decision‐tree algorithms (e.g., CART, C4.5) and ensemble methods like random forests, where statistical rigor in splitting criteria and robust handling of missing data remain critical. Its emphasis on automated, hypothesis‐driven partitioning has influenced automated feature selection, interpretable machine learning, and scalable analytics workflows that transform raw categorical variables into actionable insights.

Data Science #28 - The Bloom filter algorithm

In the 28th episode, we go over Burton Bloom's Bloom filter from 1970, a groundbreaking data structure that enables fast, space-efficient set membership checks by allowing a small, controllable rate of false positives.Unlike traditional methods that store full data, Bloom filters use a compact bit array and multiple hash functions, trading exactness for speed and memory savings. This idea transformed modern data science and big data systems, powering tools like Apache Spark, Cassandra, and Kafka, where fast filtering and memory efficiency are critical for performance at scale.