Forget Romeo and Juliet or Cleopatra and Marc Antony. At least when it comes to politics, one of the great love affairs of all time may have been between Lyndon Johnson and… himself.

Johnson leads the list of 42 presidents on measures of “grandiose narcissism,” according to a new study by a team of psychologists published online by the journal Psychological Science.

Also near the top of presidents grandly infatuated with themselves were Teddy Roosevelt, Andrew Jackson, Franklin D. Roosevelt and John F. Kennedy. Bringing up the rear: Millard Fillmore, James Monroe, Grover Cleveland and Ulysses S. Grant.

Finishing squarely in the middle—not too humble, not too bigheaded, just about right—were some of America’s nice-guy presidents: Dwight Eisenhower, Jimmy Carter and George Washington. (Barack Obama was not rated.)

These researchers also found that, on average, presidents are more narcissistic than the average American. Moreover, the level of grandiose narcissism in presidents has increased in recent decades.

First, how do you measure narcissism? Grandiose narcissism is a distinctive type of narcissism characterized by exhibitionism, attention-seeking, inflated demands of entitlement and denial of weaknesses.

To compile their rankings of most and least grandiosely narcissistic presidents, these researchers assembled data from three major sources. The heart of their analysis is data collected as part of an earlier study of the personality characteristics of all U.S. presidents through Bill Clinton, which they supplemented with data on George W. Bush. 

For this earlier study, 120 “expert raters” evaluated presidents by filling out standardized personality tests, using their knowledge of the presidents to inform their answers. The raters included historians, presidential biographers and other scholars. For each president that fell within their area of expertise, these raters answered nearly 600 questions on the personality and behavior of their president or presidents. The questionnaire included measures that are used to diagnose various psychological conditions, including grandiose narcissism. Separate questions assessed other aspects of presidential character including unethical behavior.

A caveat:  Comparing one president’s ranking with another should be done cautiously because raters only evaluated presidents they were knowledgeable about and not all first executives. Beyond that, these ratings are based, in part, on personal opinions, albeit the judgments of well-informed experts—another reason for caution.

The research team supplemented these data with historical surveys of presidential performance. They included a 2009 C-SPAN survey of 64 historians who rated the presidents on 10 dimensions, including overall job performance, persuasiveness and crisis management. They also analyzed a 2010 Siena College survey of 238 historians who ranked the presidents on 20 dimensions of performance and an academic study summarizing a dozen rankings of the presidents.

Finally they added object measures of presidential performance to this statistical stew.  These included overall share of the vote, number of terms and total years served, scandals in office and whether the president was subject of one or more congressional impeachment resolutions.

The research team found that a generous helping of inflated self-worth is a “double-edged sword” for presidents.

On the one hand, Ashley L. Watts and her colleagues found grandiose narcissism was associated with “superior overall greatness” as measured by historians’ rankings of presidential stature and “positively associated with public persuasiveness, crisis management, agenda setting and allied behaviors.” And when they looked at objective measures of presidential performance, researchers found that grandly narcissistic presidents won a larger share of the vote and initiated more legislation than less self-infatuated first executives.

But there’s also a dark side to grandiose narcissism—the painful cutting edge of Watts’ double-edged sword. Leaders ranking higher on this narcissism measure also were more likely to be the targets of impeachment resolutions (Richard Nixon stood sixth on the list, just behind Kennedy) and engage in unethical behavior (Bill Clinton ranked seventh).

The researchers also examined another type of narcissism called “vulnerable narcissism” and duplicated the index used to clinically diagnose narcissistic personality disorder (NPD). That measure is based on a combination of markers of grandiose and vulnerable narcissism.

No matter. Johnson still leads the presidential pack, again finishing first on the NPD index and fifth on the measure of vulnerable narcissism.

Members of the study team included Ashley L. Watts, Scott O. Lilienfeld, Sarah Francis Smith and Irwin D. Waldman of Emory University; Joshua D. Miller and W. Keith Campbell of the University of Georgia; Steven J. Rubenzer of Concord, New Hampshire and Thomas J. Faschingbauer of the Foundation for the Study of Personality in History, Houston, Texas.

Rich Morin  is a former senior editor focusing on social and demographic trends at Pew Research Center.