In an October 2012 report titled “Primary Elections and the Quality of Elected Officials,” Columbia and Harvard University professors Shigeo Hirano and James M. Snyder assert that primary elections have been historically underestimated in value.
According to the report, “those skeptical of the value of primary elections often point to the fact that few incumbents are even contested in their primary, let alone fiercely challenged.”
The overall level of competition in incumbent-contested primaries has steadily declined since the 1930s. In fact, the degree of competition in incumbent-contested primaries is so minimal on average that many conclude that primaries matter “little or not at all.” In the 2000s, the overall level of competition was “dismally low,” with only 31 percent of incumbents contested in strong party primaries and only 6 percent in weak party primaries.Credit: Shigeo Hirano and James Snyder
However, Hirano and Snyder argue that it is not clear that the lack of competition should be a major concern, explaining that, since incumbents appear to be of higher quality than the “pool” of candidates, it is possible few incumbents deserve to be removed or even strongly challenged in their parties’ primaries:
Why should we think that, under normal circumstances, there are candidates available to a party who clearly dominate the incumbent? Incumbents have experience and seniority, and track records that prove they can win elections. Given the large incumbency advantage that exists in general elections, a party would be reluctant, especially in competitive districts, to give up this electoral advantage unless the alternative was clearly superior on some dimension of value to the party. Such challengers may be rare. Given the costs associated with competitive primaries - borne by candidates, government and voters... it is probably more efficient to allocate scarce ‘primary election resources’ to open seat races and incumbent-contested races in the rare case where incumbents are low quality.
Although they acknowledge that it is “extremely difficult to measure either the quality or performance of politicians,” they claim that open-seat races tend to result in higher-quality winners: “If open-seat winners are high-quality, then most incumbents will be high-quality as well, since most incumbents were, at some point in the past, open-seat winners.”
Consequently, Hirano and Snyder express particular care about how well the electoral system works in open-seat races where there's increased competition leading to higher quality politicians.