"regional factor" is a correct and usable phrase in written English.
You can use it when you are referring to an influence or element that is specific to a region or location. For example: Many people in the area take into account the regional factor when making decisions about where to live.
Incorporating host species (peach or apple) rather than geographic region as the "regional" factor revealed that host species did not account for any of the variation in the data set, while variation within and between populations accounted for 70% and 30% of the variation, respectively (P < 0.001).
Volcanic activity was another regional factor influencing different landscape components.
The World Trade Model with Bilateral Trade (WTMBT) (Strømman and Duchin 2006) is a linear program that minimizes global factor use to satisfy consumption requirements while respecting regional factor constraints.
Such assumptions seem reasonable when separate sites some distance apart show the same chronology of events, or at least clusters of events, suggesting that some kind of regional factor influenced the behaviour of TCs at different times during the past.
This regional factor accounts for the increase of the Earth's main magnetic field with latitude and is given by (see for example Love and Constable 2003, their Equation 48): F_{latitude}=1+3sin(lat)^{2}, (18).
Figure 5 shows regional factor loading profiles for TSR1.
Marieestelle and Facchini (2013) finds Okun's Law holds for fourteen French regions but breakdowns for eight regions and identifies regional factors to explain the disparities.
Differences between the regions imply that there are regional factors that are responsible for the variation.
To account for differences in exposure and other unmeasured regional factors, we also controlled for U.S. geographic region of residence (Northeast, South, Midwest, West).
Regional factors help explain this disparity.
Regional factors must also be taken into account.
