Disclaimer. Don't rely on these old notes in lieu of reading the literature, but they can jog your memory. As a grad student long ago, my peers and I collaborated to write and exchange summaries of political science research. I posted them to a wiki-style website. "Wikisum" is now dead but archived here. I cannot vouch for these notes' accuracy, nor can I say who wrote them.
Arriola. 2005. Where there is no alternative: Explaining weak opposition weakness in sub-saharan Africa. APSA convention.
Though scholars typically cite the failure of African oppositions to coordinate as the cause of long-lasting incumbencies, Arriola notes that there is actually considerable variation among African states concerning the opposition parties' ability to coordinate, and in many (44%) elections the opposition does coordinate to a degree. What determines the opposition's ability to coordinate?
Y: The probability of opposition coordination (dichotomous)
X1: Government's control of the economy. Measured as "government consumption as a percentage of GDP."
X2: Uncertainty within the opposition of each party's relative strength. Measured as "the difference in size between a country's two largest ethnic groups."
Research on similar subjects