These findings should remind us that basically every assessment of the popularity of a major public figure should include some reference to the economy. Sadly, very few of these do.
Try this as an experiment. Ask a group of students, or political reporters, or pretty much anyone why Reagan was a popular president. You'll probably get a range of answers talking about his charm, his charisma, his folksy story-telling, his deftness in dealing with the Soviets, etc. But, of course, the actual answer is that the economy was growing pretty strongly during much of his tenure. Furthermore, he wasn't always popular:
Reagan was actually pretty unpopular for much of his first term. Why? Wasn't he still charming and charismatic? Wasn't he telling his folksy stories? Well, sure, but the economy was tanking. Once it started growing steadily, so did his approval ratings, until the big drop in the second term as a result of the Iran-Contra scandal. Which makes you think -- what if that scandal had happened during a recession, when Reagan's approval ratings were already in the low 40s. If he'd dropped into the 20s, would he have been impeached?