The Availability Bias

When we think about if the world is getting more violent, we can easily recall many horrific examples of violent crime.  We think of the terrible things we have seen on the news and online.  However, the real question is - 'how likely is a person to be a victim of violence or war?'  Is it more or less likely than 50 years ago?  Our brains are not equipped to handle that question!  How can we make sense of the number 7 Billion (people on the planet) versus the incidence of violent crime?  We can't!  What we can do is recall the many terrible events we learned about on the nightly news.  So our brain substitutes something that is Available (easily recalled examples) for something that is not.  This is now a well understood flaw.  It is referred to as the 'Availability Heuristic' or the 'Availability Bias'. 
Daniel Kahneman and Amos Tversky won a Nobel Prize for this (and other discoveries) in 2002!

The Negativity Bias

From Brecht Vandenbroucke's excellent article in Wired.
When we hear negative statements, we think they’re inherently more intelligent than positive ones. Teresa Amabile, director of research for Harvard Business School, began exploring this back in the 1980s. She took a group of 55 students, roughly half men, half women, and showed them excerpts from two book reviews printed in an issue of The New York Times. The same reviewer wrote both, but Amabile anonymized them and tweaked the language to produce two versions of each—one positive, one negative. Then she asked the students to evaluate the reviewer’s intelligence.
The verdict was clear: The students thought the negative author was smarter than the positive one—“by a lot,” Amabile tells me. Most said the nastier critic was “more competent.” Granted, being negative wasn’t all upside—they also rated the harsh reviewer as “less warm and more cruel, not as nice,” she says. “But definitely smarter.” Like my mordant tweets, presumably.
This so-called negativity bias works both ways, it seems. Other studies show that when we seek to impress someone with our massive gray matter, we spout sour and negative opinions. In a follow-up experiment, Bryan Gibson, a psychologist at Central Michigan University, took a group of 117 students (about two-thirds female) and had them watch a short movie and write a review that they would then show to a partner. Gibson’s team told some of the reviewers to try to make their partner feel warmly toward them; others were told to try to appear smart. You guessed it: Those who were trying to seem brainy went significantly more negative than those trying to be endearing.