WaPo fact checker Michelle Ye Hee Lee had this article Thursday on President Obama's various statements after mass shootings, which are not fully consistent with each other or with the facts.  The article also has a cautionary nugget about what "experts say" and what "studies show."

Mr. Obama gets the maximum Four Pinocchios (reserved for "whoppers") for his December 1 statement in Paris, "I say this every time we've got one of these mass shootings: This just doesn't happen in other countries."  Wow.

The President's other, more nuanced statements about the relative frequency of such incidents get the milder Two Pinocchio rating ("significant omissions and/or exaggerations").  To check the facts, Ms. Lee consults experts Adam Lankford and John Lott and gets very different answers.

Astute readers might notice how Lankford and Lott both compared the United States to grouped European countries, but their conclusions are vastly different. Lott says the rate is about the same, while Lankford says the rate is five times higher in the United States. How is this possible? The researchers are looking at different sets of years and different sets of countries. (Lott looked at Europe as a whole; Lankford at the European Union.) Lott uses a broader measure of mass shootings than Lankford does. Lankford looks at the number of shooters; Lott uses fatalities and shooting incidents. This is an example of how the data and definition can be adjusted to show different findings about mass shootings, even using a per capita rate.

Lots and lots of choices have to be made in setting up a study, many seemingly benign in themselves.  If a person wants to reach a particular result, it is easy as pie to run the numbers 16 different ways, pick the way that best supports your agenda, and throw the others in the trash.

This is why the viewpoint one-sidedness of American academia and the well-funded nonprofits is so very dangerous.  The truth comes out much more clearly when there are people on both sides doing these kinds of studies, but academic conservatives are an endangered species, and those who do "come out" are targeted by neo-McCarthyists determined to achieve ideological purity.

Be very, very skeptical about what "studies show" and "experts say."