From an interesting psychological profile of Trump in The Atlantic:

Assessing the truthfulness of the 2016 candidates’ campaign statements, PolitiFact recently calculated that only 2 percent of the claims made by Trump are true, 7 percent are mostly true, 15 percent are half true, 15 percent are mostly false, 42 percent are false, and 18 percent are “pants on fire.” Adding up the last three numbers (from mostly false to flagrantly so), Trump scores 75 percent. The corresponding figures for Ted Cruz, John Kasich, Bernie Sanders, and Hillary Clinton, respectively, are 66, 32, 31, and 29 percent.