In astronomy, one of the most important things we have to keep in mind when we look at observational data is the possibility of “selection effects.” Sometimes we can be fooled by drawing conclusions about what we see, if we don’t factor in what’s EASY to see. (1/5)
One famous selection effect is in the search for exoplanets — planets around other stars. At first, we saw mostly “hot Jupiters” (large planets close in). If we’d assumed we had a fair sampling of all exoplanets, we’d have thought most are hot Jupiters (pic: ESA/C. Carreau) (2/5) 
Turns out, hot Jupiters were just particularly easy to spot, using techniques like the radial velocity method. That’s where we see from changes in a star’s light that a planet is tugging its star around as it orbits. Big planet close in = stronger effect. (Gif: @AstroAlysa) (3/5)
There are selection effects all over astronomy, like in the fact that we see very massive galaxies far away (the distant small ones are too dim to see). You probably see stuff like this yourself & correct for it, knowing you’re more likely to notice more noticeable things. (4/5)
It’s good to keep selection effects in mind when looking at human behavior too. Polls (& other data) show that right now, most people are safety conscious, social distancing, using masks. When you see pics of big parties, keep in mind you don’t see everyone who stays home. (5/5)
