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Estimating Initial Probability: Don’t Forget the Prior!

Overlooking the Initial Probability

One common trap of human intuition is failing to take into account the plausibility of an event before considering the context-specific evidence of the case at hand. Without knowing how plausible a hypothesis is in general, it is easy to fall into the trap (test yourself!) of overestimating the initial probability for inherently unlikely theories. This is known as the Prosecutor’s fallacy, one of the main flaws of human reasoning.

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When Logic Goes Wrong: Survival Guide

Logic Is Dead

As discussed in a previous post, logic fails in the real world. Real-world problems do not lend themselves to logical reasoning since any non-trivial issue involves some uncertainty (Was the report accurate? Is the test result a false-positive?). When the problem is also complex, involving large amounts of information with intricate dependencies, then uncertainty can render the logical argument meaningless.

How Does Anyone Make Decisions?

Given these hurdles, how has humanity managed to make any progress at all? How do we deal with uncertain information in cases of high complexity? Continue reading

Aerophobia: Fighting Heuristics with Probability

Heuristics: Decision-making Shortcuts

What are you more afraid of: boarding a plane, or getting into a car? For many people, flying comes with nervousness or trepidation. Such concerns don’t reflect realistic concerns. Car crashes claim more lives each year by orders of magnitude. But they do reflect something else: a cognitive trap to which almost everyone is susceptible.

Making decisions can be difficult. To help us along, our minds use a number of cognitive shortcuts. These shortcuts, called heuristics, allow us to make more rapid decisions with minimal calculations. Unfortunately, while generally efficient, heuristics can also lead us astray.

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Every Logical Argument You Ever Made Was Wrong

Isn’t Logic Great?

Who doesn’t like logic? We idolize Sherlock Holmes’ ability to solve mysteries by “eliminating the impossible.” In arguments with friends, we try to prove we’re right using logic, rather than intuition or emotions. And we especially enjoy pointing out others’ logical fallacies–preferably using latin terms.

Don’t pat yourself on the back just yet. Finding logical fallacies is actually much less impressive than you might think. That’s because in the real world, all arguments violate the principles of formal logic.

Yes, perhaps every logical argument you have ever encountered was flawed.

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Ghouta Attack: Challenging Conventional Wisdoms

Ghouta Attack

On August 21, 2013, the war in Syria reached a new low. Horrific pictures and stories began to spread about an attack near Damascus. Reports of chemical weapon use in the Ghouta region soon followed.

It was soon confirmed that there had indeed been a chemical attack. Deadly sarin-gas rockets had hit multiple areas within the Ghouta region, causing hundreds of casualties. But while there had clearly been an attack, its origins were less obvious. Syria, Russia, the US, UN, and opposition fighters all argued about who was responsible. These claims often reflected political interests more than truth-seeking. At Rootclaim, we set out to sift through the evidence in search of more objective conclusions.

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MH 17: Weak Evidence Matters

Discounting Weak Evidence

One pitfall to avoid is prematurely discounting seemingly weak evidence. Weak evidence can take many forms. It could be evidence that seems very unlikely under all hypotheses. Or it could be evidence that is non-intuitive and doesn’t seem to fit what we consider “conclusive” evidence.

When evaluating evidence, it’s easy to get distracted looking for “irrefutable” evidence (more on that in an upcoming blog post). However, that’s a mistake. What’s really important is the ratio between how likely evidence is under the hypotheses.

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Evidence in Flight 370: Snowflakes Add Up

Strength in Numbers

How much does a snowflake weigh? How about a drop of water? If you’ve ever shoveled snow, or picked up a large jug of water, you know that the weight adds up. The same principle holds true with evaluating evidence. When starting an analysis, we often find little hints that slightly support one hypothesis over the other. Many people might think that these clues wouldn’t really have an impact. Or they might assume that a piece of evidence with a significant influence on the hypotheses renders other evidence meaningless.

However, just like snow, those little pieces of evidence can add up. It’s hard to shovel up thousands of snowflakes at a time (even though individually they’re almost weightless). Likewise, enough evidence pointing in the same direction can have a weighty influence (even if each individual “proof” is not that strong independently).

 

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Getting to the Essence

On Monday, John went to the mall. John left Green’s Grocery at 7:47 AM and drove home in his 2007 Honda Pilot. John forgot his blue umbrella in the store. That night John’s neighbor Martha, a retired engineer who lives down the block from him, called him. Martha had found the umbrella and was coming to return it. Is that a miracle? Or a largely predictable outcome? The answer depends on which of the many coincidences we consider.

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Calculating Accurate Inputs

Serial: A Game of Numbers

Every analyst has their methods: take a poll, measure social media buzz, weigh various key factors. Rootclaim’s analysis of Serial: Who killed Hae Min Lee provides a good example of how the Rootclaim system uses hard numbers in order to “calculate reality” – to determine mathematically which hypothesis is the most likely.

Rootclaim recently took on one of the most controversial criminal convictions: that of Adnan Syed, sentenced to jail for murdering his ex-girlfriend Hae Min Lee. Syed’s conviction has been featured in the podcasts Serial and Undisclosed, and followers of the case have debated the minutiae on forums such as Reddit. Until now, discussion forums have focused on how a few particular pieces of evidence proved one hypothesis or another. Rootclaim has put together the first concerted effort to gather all the relevant information into one cohesive analysis.

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Innoculate Your Arguments with Data and Reason

The MMR Vaccine Controversy

The controversy over whether and how often to vaccinate children remains a volatile one. But how much does this debate match the empirical data and objective reasoning? The Rootclaim analysis of the MMR vaccine and its alleged ties to autism illustrates the challenges of objective, rational decision-making. Continue reading

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