Can you have causation without correlation? (Surprisingly, yes)

March 14, 2022

Usually, when X causes Y that means that X is correlated with Y. This may seem obvious simply because correlation is simply a measure of the extent to which Y goes up, on average, when X goes up. But, fascinatingly, there are some special cases where you can have causation WITHOUT correlation. Here are five ways causation without correlation can occur: 1. Averaging: increasing A sometimes causes increasing B, but other times, it causes B to decrease. The two balance out. Since correlation...

It can be shockingly hard just to understand three variables

April 19, 2021

In science (and when developing hypotheses more generally), it is very common to come across situations where a variable of interest (let’s call this the dependent variable, “Y”) is strongly correlated with at least two other variables (let’s call them “A” and “B”). Here are some examples: If you’re a psychology researcher investigating possible causes of depression (Y), you may have trouble disentangling the effects of poor sleep quality (A) and anxiety (B), both of which tend to be corre...

What’s the link between depression and anxiety?

January 10, 2021

This image is from my colleague Amanda Metskas’ post on the Clearer Thinking blog, “Understanding the two most common mental health problems in the world:” https://www.clearerthinking.org/post/understanding-the-two-most-common-mental-health-problems-in-the-world

If you study depression and anxiety (in the U.S.), you find that they are correlated to a shockingly high degree (e.g., in one of my studies, when I correlated PHQ-9 depression scale scores with GAD-7 anxiety scale scores, I found that r = 0.82 ). Additionally, many studies have found that SSRIs (and other medications) help people with both depression and anxiety, as do certain therapeutic modalities such as Cognitive Behavioral Therapy, suggesting further linkage. Fin...

The Relationship Between Personality and Life Satisfaction

November 16, 2018

What's the relationship between personality and life satisfaction? We took a stab at figuring it out! We conducted a study of 999 people in the United States; recruited through our study platform at Positly.com. We looked for a correlation between 18 different personality traits (each trait being assessed with two questions) and life satisfaction. We examined the association each trait had with scores on the Satisfaction With Life Scale (a 5 question scale by Diener, Emmons, Larsen, Griffi...

What is a large correlation? Looking at the sizes of 166 correlations.

January 13, 2018

How large is a "large" correlation when it comes to studying people? Below are 166 (rather interesting!) size-ordered correlations that I calculated on 870 people in the United States, who were recruited using our study recruitment platform, Positly. All responses are self-reported by the study participants, mostly measured on a scale of 1-4 or 1-5, except those that suggest a different scale (e.g., number of minutes doing something, age, symptom scores, etc.) Keep in mind that if A an...

Correlation Coefficient as a Gateway to Skepticism

June 14, 2017

The correlation coefficient as a gateway to radical skepticism:Suppose you calculate that two variables are moderately correlated. For instance, you find that self-reported happiness has a correlation r=0.32 with self-reported willpower, as I found in one of my studies. What are the possible explanations for (or causes of) this? A Causes B - Increasing A is a cause of increasing B but not the reverse. [e.g., more happiness causes more willpower] (2) B Causes A - Increasing B is a cause ...

How Journalism Distorts Reality

April 7, 2012

Journalism provides us with important information about what's going on in the world. But when you consider the incentives that journalists have, combine that with their usual lack of scientific training, and add in the constraints of the medium in which they work, serious distortions of reality can result. Many journalists produce excellent work. But others leave you less informed after reading their articles than before you began. What causes journalistic distortion? 1. Equal time to eac...