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 even say who wrote them. If you have more recent summaries to add to this collection, send them my way I guess. Sorry for the ads; they cover the costs of keeping this online.
Hicken. 2005. Engineering aggregation? Institutional reform and party aggregation in Thailand. unpublished.
Hicken must have read Cox (1999)--wherein Cox laments the dearth of studies of linkage--and decided to run with it. He modifies Cox's model slightly (though I'm not sure he improved on it).
Incentives (expected utility) for linkage/aggregation (Y) depend on the expected payoffs of aggregation. This has three components (two payoffs, one probability):
Hicken decides to split Cox's variable (centralization of power) into two variables, vertical and horizontal centralization. Vertical centralization is a fancy way of saying "federal or unitary?". Horizontal centralization is the rest: presidentialism, bicameralism, and other veto players. Hicken claims that nobody else has ever considered horizontal centralization, which is untrue (Cox 1999). Why he split centralization into two dimensions escapes me. He should have just used one variable: the number of elected veto players (checks and balances) in the governmental structure. If there are more checks on the governments (more veto players), then the potential payoffs of aggregating/linkage are diminished.
Hicken is vague on presidentialism/parliamentarism (p 7-8). He starts by calling presidentialism less attractive, but then says that the stronger the president is, the stronger the incentives for linkage. Presumably, then, there is a point at which a strong president creates better incentives for linkage than a parliamentary system. (Makes sense, I suppose: The strongest presidents/dictators have no checks on their power.)
Institutional rules affect the probability that the largest power will gain control of government. Some countries automatically give the largest party the first chance to form a coalition. In other countries, the first coalition to pass an investiture vote gets the premiership. These rules affect the probability that becoming the largest party is worth it. After all, if you can form a coalition later, why aggregate now?
He tests his theory in Thailand, where there is less linkage than we might expect by looking at federalism alone (Thailand is unitary). He attributes this to a few factors: checks on the government (low payoffs) and no guarantee that the largest party will get the premiership (in fact, non-politicians were awarded the premiership several times in the 1980s and 1970s).
Then, in 2001 elections, a new constitution was in place. For the first time, a single party won almost a majority of the legislative seats; ENPP fell dramatically. Why? The new constitution decreased district magnitude (thus fewer parties at the district level), increased the prime minister's powers (thus greater incentives for aggregation), replaced the appointed (by military and bureaucracy) Senate with an elected one (thus Senate was less of a check to a strong party in the House), and decentralized political and economic power (should make aggregation less likely, but hadn't taken effect yet in 2001).
Research on similar subjects