In a 30-30 state House like Oregon’s, with an election coming up, every seat matters. A lot. So who’s sitting on the hot seats?

You can look at this from various directions, not all of them strictly statistical. Such matters as quality of candidates, gaffes and other negatives and the strength of a challenge matter. And, of year, money too. But party identification, in these very partisan times, matters a whole lot, and one useful place to start may be a look at what legislators are representing the most politically divided districts – or districts in which the other party has a registration advantage. (The registration numbers are those for February, posted by the Oregon Secretary of State’s office.)

Based on material from the upcoming Oregon Political Field Guide

In that last category, of legislators who have partisan minorities in their districts, there are six, all Republicans.

By this standard, the single most endangered Republican should be Katie Eyre Brewer of Hillsboro, in District 29. The district has a Democratic edge of 6.62%, and Brewer won with 53% in a relatively low-turnout year. She pulled a record Republican vote in this district, but Democrats exceeded her raw totals both in 2008 and 2004; and this year, like those, is a presidential. She’s at high risk.

The second most endangered Republican on this list would be Patrick Sheehan, of Clackamas, in House District 51. This district (well, its analogue before redistricting) was Republican a decade ago, and decisively into 2006, but clearly Democratic in the last two cycles – presently by a margin of 6.47%. Sheehan won his first term in 2010 with a respectable 54.57%, but his vote total was lower than the last Republican there, Linda Flores, had two years before that when she lost the seat. If turnout is up this year, Sheehan could be at big risk.

Brewer and Sheehan both represent districts with higher Democratic edge than the district held by the top-ranking House Democrat, Arnie Roblan of Coos Bay.

The other four Republicans in tough terrain are Shawn Lindsay of Hillsboro (District 30), Mark Johnson of Hood River (District 52), Jason Conger of Bend (District 54) and Julie Parrish of West Linn (District 37). All but Parrish unseated Democrats in the Republican tide year of 2010.

And it should be noted that the comparisons aren’t totally apples and apples, since the districts have been redistricted. But in most cases that doesn’t seem likely to make a big difference.

If that sounds like the makings of a Democratic target list, who should be the Democrats on the Republican short list?

There are no Democrats representing Oregon House districts with Republican registration leads. The closest would be District 9 – the Coos Bay district Roblan, the current House co-speaker, is leaving to run for the Senate. That district could have the makings of a serious contest.

After that, the going gets tougher. The Democrat in the next most marginal district is Deborah Boone (of Cannon Beach) in District 32 (Democratic edge: 8.8%), based in Clatsop County. She had a close race in 2010 (winning with 52.31%), but won easily earlier; and her new district should be more helpful to her than the old one was.

The next three districts in relatively small Democratic advantage are districts 40 (an open seat, with Dave Hunt‘s departure for a county race), 50 (Greg Matthews of Gresham) and 22 (Betty Komp of Woodburn). None look like easy catches.

In a race where such large results can turn on small conditions, the future of the Oregon House is far from settled. Based on party registration, Democrats have an early advantage.

What about other measure?