Main question, how exactly does one match "a healthy economy" with a presidential election result? When you say, "healthy economy" what do you mean exactly?
Well, GDP and overall economic growth is a better indicator than the unemployment rate, but more than that, "a healthy economy" correlates most closely to psychological mood of the people in general. That mood can be, and often is (especially in an election year) manipulated, as all thing psychological are wont to be. But in particular, economic "experts" can proclaim the economy is bad, or certainly will be soon, and that consumer confidence is down, or will be soon, and little by little it becomes a self-fulfilling prophecy, thanks to businesses and consumers latching onto the fear and uncertainty and suddenly stop spending and/or expanding. This can happen when all of the classic economic indicators show the opposite, and in a good economy. Election years in and of themselves do not have a negative effect on the economy, except for the fact that copious amounts of news reports of doom and gloom suddenly start appearing in an election year, particularly when such reports can hurt the incumbent (or the incumbent of the party). It's fascinating to watch, albeit predictable.
So, by "a healthy economy" I mean the perception of the voters. In polling, if the question asked is "Do you think the economy is on good shape?" or "is headed in the right direction?" If the answer is NO, whoever gets the credit or the blame for that perception will have a very tough time winning the presidency. Couple a NO answer with with "Who is better qualified to handle the economy?" and there's your likely winner.
All throughout the campaign, economists (who are wrong at an astonishing rate) overwhelmingly (two-thirds) preferred Clinton or Johnson to Trump. Yet the voters preferred Trump by the same staggering proportions in polls throughout the campaign. And exit polling by voters showed that the same two-thirds of all voters thought A), the economy was bad, and B) Trump would handle it better than Hillary (90-something for Republicans, 50-something for Democrats).
To have a proper discussion about this, is it not first necessary to define what we mean by "the economy?"
Well, I'm not all that certain I want to have a proper discussion on this topic, because while it is somewhat interesting to me in the psychology of the social science realm, it's mostly boring (both for me and I would imagine nearly everyone reading this thread). And I don't think a proper discussion will end with any kind of agreement, as the entire topic is more one of an ongoing intellectual pursuit of study than anything.
But since you asked, as with most intangible things, particularly opinions, it can mean whatever you want it to mean. I look at the perception of the populace, and at the newspaper headlines during the campaign, and draw my conclusions accordingly. If the populace perceives the economy to be good or bad, then that's what it is. And people vote their psychological perceptions.
There are, as I said, plenty of exceptions to this. For example, even if the economy at the time was the bestest of the best, both in reality and in perception, there was no way Jimmy Carter was going to be re-elected.
Between Trump and Hillary, Trump clearly has more (perceived) experience in handling an economy, so between those two it seemed like it would be, and was, a slam dunk. Having said that, both Hillary and Trump were perhaps the two luckiest major party presidential candidates in history, as each was running against the only person they could have beaten. <snort>
Excerpt: "The first thing to notice is that no individual economic variable has an r-squared higher than .46, meaning that none [of the economic indicators] can explain more than half of election results in the post-war period."
Excellent example of the aforementioned studies that go to great tortured lengths to dispel the conventional wisdom, in the quest to academia-ize it with some magical mathematical formula that can be a quantifiable predictor.
