Seasonally adjusted flow from BEA, NIPA, Table 1.5.5, line 49, Imports. Prior to 2007, unadjusted flow from BEA, NIPA, Table 8.1, line 17, Imports. Seasonal factors are calculated as the seasonally adjusted flow at an annual rate, divided by four, less the unadjusted quarterly flow. Beginning in 2007, unadjusted flow is equal to the seasonally adjusted flow divided by four and seasonal factors are zero. Series has no levels.