I admit to a belief based on no data: large law departments always have some rainy day cash they can spend. General counsel of big departments steward large budgets and can almost always find funds, if they want to, to pilot a program, hire a consultant, invest in new software, run a study or otherwise invest capital. Over time, the availability in larger departments of discretionary funding of fertilizes improvements, which lowers total legal spending as a percentage of revenue and lawyers per billion (See my post of Aug. 21, 2008: total legal spending as a percentage of revenue (TLS/Rev) with 9 references and one metapost; and Feb. 25, 2009: lawyers per billion with 22 references and one metapost.).
Small law departments, with nowhere to scrounge funds and little fiscal flexibility, can’t innovate as easily. With tiny or no slush funds, they lose the compounding improvements of investment and fall behind in the productivity competition with larger departments.