Bayes' theorem lets you flip a probability around to find the cause from the effect

science & techWikipedia18th century

Bayes' theorem lets you flip a probability around to find the cause from the effect

the gist

Bayes' theorem is a rule for reversing conditional probabilities. It lets you work out the chance of a cause from the effect you observed. A medical example: if a test is positive for a disease, the theorem combines how accurate the test is with how common the disease is, to show how likely the patient really has it. Thomas Bayes developed it in the 18th century, and Pierre-Simon Laplace independently developed the same idea.

how it works

The theorem multiplies the prior chance of a cause by how likely the effect is if that cause is present, then divides by the overall chance of the effect. Starting from how common something is in the population, new evidence updates the estimate step by step.

so what

The theorem underpins modern statistics, spam filters, medical diagnosis and machine learning. It explains why a very accurate test can still give mostly false alarms when a disease is rare.

the bigger pattern

Bayesian reasoning is used to revise beliefs in fields from forensics to weather forecasting. The same base-rate logic explains why rare conditions produce many false positives.

Hampi was once one of the world's largest cities, until its Vijayanagara capital was destroyed in 1565

the gist

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.

how it works

The city was built around a fortified core with temples, markets and water structures along the river, supplied by an extensive network of roads and waterworks. When the empire fell, the city was not rebuilt, so its stone monuments were left standing.

so what

Hampi shows how quickly a great city can vanish after a military defeat, and how a ruined capital can remain sacred. Its ruins give historians a view of medieval South Asia that few other sites can match.

fun fact

The name Hampi comes from Pampa, an old name for the Tungabhadra River.

From Wikipedia, the free encyclopedia · text CC BY-SA 4.0

Image: Wikimedia Commons

source: Wikipedia ↗

2 min

politicsshortCNA2:01

False allegations about Singapore’s hand in Indonesia’s markets and a made-up meeting

from CNA

CNA Verify has found close to 400 posts pushing falsehoods tying Singapore to Indonesia’s stock market rout and to a secret meeting that never took place. Together, they drew nearly 12 million views, and some were circulated by accounts that appeared to be working in concert, across multiple social media platforms.

Here’s how the disinformation campaign targeting Singapore was uncovered.

on YouTube: CNA ↗