Why is the TRAC data in index form instead of actual numbers?
Since our data is based on surveys, we do not attempt to say how many loads were transported by all for-hire carriers. Instead, the data should be used to look at trends and percent changes. Several government economic indicators are also in index form, like the Federal Reserve’s Industrial Production. ATA’s monthly truck tonnage indicator is also an index. What is seasonally adjusted data? Our seasonally adjusted indexes have been “adjusted” to remove effects of changes that normally occur around the same time every year (holidays, the fall freight season) as well as the days of the month, which can increase or decrease freight volumes simply because there are more or less days compared to the previous month. Seasonally adjusted data should isolate trends or changes due to the business cycle and not due to reoccurring annual events. How does ATA seasonally adjust the data? An adjusted index is obtained by applying statistical seasonal coefficients to the unadjusted index. Those coeffi
