An autoregressive distributed lag (ARDL) model was
developed and used with OLS regression analysis. Traffic
was regressed onto similar explanatory variables as in prior
models, but also onto lagged values of traffic. The inclusion
of lagged values of the dependent variable (traffic) is
done to account for the slow adjustment of supply (in the
form of capacity) to changes in the explanatory variables.
The applicability of this assumption is less reasonable for
the U.S. domestic market as the barriers to expanding
capacity are fewer than on international routes; the U.S.
domestic market was therefore excluded from ARDL
estimation16