Prakash Adhikari has a paper in the AJPS (PDF, gated) that seeks to address this question:

This study investigates circumstances that affect individuals’ decisions of whether or not to flee their homes during civilian conflicts. Building on the “choice-centered” approach to studying forced migration, I test the argument that people make a decision to flee or stay even under highly dangerous circumstances. Using primary data collected through a public opinion survey in Nepal, I test a number of hypotheses regarding the impact of factors such as violence, economic opportunity, physical infrastructure or geographical terrain, and social networks on forced migration, providing an individual-level test of the choice-centered approach to studying forced migration. The empirical results are consistent with the major hypotheses developed in aggregate-level studies and provide better insightsinto the factors that affect individual-level behavior. Beyond conflict, there are a number of significant economic, social, physical, and political factors that affect individuals’ choice to flee.

As expected, the threat of violence and actual experience of violence increases the likelihood that one would flee – by about 8 and 32 percentage points respectively. Economic opportunity, on the other hand, reduces the likelihood of fleeing by 19%. High income individuals are also less likely to flee by about 1-2%. In addition, social ties decrease the likelihood of fleeing, although the effect is not statistically significant in Adhikari’s model.

The paper primarily looks at conflict, but may also apply to cases of overall economic collapse and political turmoil as has plagued Zimbabwe in the last one and a half decades. It is estimated that almost a quarter of Zimbabweans have fled the country. But three quarters remained, through the hyper-inflation and acute restriction of political space and personal freedoms.

In particular, the Zimbabwe case provides a good case for knowing why elites (who presumably can leave if they want) choose to stay in states like Zimbabwe – and thereby continue to provide the means of survival for the regime.

For those who have chosen to stay in Zim it might be that they have a lot to lose by fleeing (they have jobs, own some property, have strong extensive social ties, are too patriotic to leave …..?) or are actually plugged into the patronage system of Robert Mugabe, supported by illicit trade in diamonds, foreign aid, and control of the economy.

H/T Joshua Keating over at War of Ideas