The 2011 TSI Bi-annual Revision
The 2011 Bi-annual Revision is performed in order to incorporate changes in methodology, revisions to the raw data (including changes in data sources), and changes in estimated weights and seasonal adjustment parameters. The Transportation Services Index (TSI) revision policy was adopted in November 2004 to balance the goals of providing the most accurate and up-to-date measure and month-to-month stability. Prior to November 2004, all data points were revised with each monthly release- in a process characterized by small but frequent changes to previously published values of the indexes. The new policy achieves greater stability by limiting changes in each data point between Bi-annual Revisions to one revision in the fourth month after its initial release. The Bi-annual Revision allows for the latest methodological research and improvements in source data to be incorporated in a systematic way and also ensures that historical data reflects recent revisions to both the raw data and to the estimated weights and seasonal adjustment parameters. This document identifies the methodological changes that have occurred since the 2009 Bi-annual Revision, serves as a reference for those changes, and conducts a detailed analysis of the effects on the TSIs of changes in the raw data, seasonal adjustment factors and weights.
METHODOLOGICAL CHANGES
Methodological changes typically consist of changes to seasonal adjustment models or to formulas underlying the calculation of the TSIs. The 2011 Bi-annual Revision does not include any significant methodological changes. Documentation for the current seasonal adjustment models can be found at http://www.bts.gov/programs/economics_and_finance/transportation_services_index/methodology/.
Methodological or Source Data Changes to the TSI
| Year of Implementation | Change |
|---|---|
| 2011, March release of January 2011 data. | No significant changes. |
| 2009 | Seasonal Adjustment models: Documentation for the current models
is available at http://www.bts.gov/programs/economics_and_finance/transportation_services_index/methodology/. |
| 2009 | Coverage for petroleum pipeline services has been expanded to capture movements for the Trans-Alaska pipeline using Alaskan field production (http://tonto.eia.doe.gov/dnav/pet/pet_sum_crdsnd_adc_mbbl_m.htm). An incorrect daily-to-monthly conversion has been eliminated. |
| 2007 | Seasonal Adjustment models: (i.e., models specified in http://www.bts.gov/programs/economics_and_finance/transportation_services_index/methodology/) Rail Freight – Intermodal: added Trading Days Waterborne: added Labor Day effects Transit: added Trading Days. Aviation – Passenger: added Trading Days. |
| 2007 | Formula for conversion of BEA value-added annual values to monthly values. |
| 2007 | Change BLS PPI for natural gas from PCU221210221210P to PCU22121022121012 |
| 2006, March release of January 2006 data. | Advancement by one month of most recent index data published with each release. |
| 2005 | Changed base year to 2000 from 1996. |
DETAILED ANALYSIS OF
CHANGES IN THE TSIs DUE TO THE BI-ANNUAL REVISION
Overview
The analysis of the effects of the Bi-annual Revision decomposes changes in each TSI index (Freight, Passenger, and Combined) into changes in the source data, changes in seasonal adjustment factors, and changes in weighting factors/methodology. The reference points used for the analysis are the TSI numbers that were revised 4 months after their initial release, but a summary of changes to the TSIs between the initial release and the 4-month revision is provided in the appendix. In what follows, we use “final” to refer to the latest data, seasonal factors, and methodology as of the Bi-annual Revision and “original” to refer to these components as of the 4-month revision for each TSI release. For example, the preliminary TSIs for December 2009 were initially released in February 2010 and were revised with the June 2010 release of the TSI (Original) and then were revised again with the March 2011 Bi-annual revision (Final). The analysis in this section with respect to the December 2009 TSIs refers to changes to the December 2009 TSIs from the June 2010 release that occurred with the bi-annual revision.
The basic model for analysis is given below:
Let t = 1,.., 228 index the months between January, 1990 and December 2008.
Let 
be the TSI index published in June 2009, without the Bi-annual Revision.
Let 
be the TSI index following the Bi-annual Revision. (Note that changes in the source data after the 4-month revision will not be reflected in in the monthly releases following the 4-month but before the annual revision.)
Let 
be the TSI index compiled using the final source data, but the same seasonal factors and weights/methodology as in .
Let 
be the TSI index compiled using both the final source data and the final seasonal factors, but the weights/methodology as in .
Then the following measures decompose the proportional changes in the TSI due to changes in the source data, seasonal adjustment factors, and weighting factors:
δt (delta) measure data changes,
ψt (psi) measure seasonal adjustment factor changes,
ωt (omega) measure weighting factor changes.
Where the following relations hold:
The Impact of Source Data Revisions on the TSIs
Data revisions received during the calendar year for each TSI component change the individual index numbers as well as the overall index. First, these revisions change the index numbers of the individual months for which source data were revised. Second, the source data revisions change index numbers for other months through their effects on the estimation of the seasonal adjustment factors, which potentially affects all numbers in the index. Third, revisions to the source data also affect the weights due to the influence on adjusted value-added. In this section we look at the effects of the first of these changes.
Table 1 shows the impact of data source revisions before seasonal adjustment. Revisions in the source data generally have a greater impact on the TSI for recent years. The largest upward revisions in the TSI indexes were: 2.39 percent for Freight in February 1991, 0.71 percent for Passenger in November 2009, and 1.75 percent for the Combined TSI in February 1991. The largest downward revisions were: 2.62 percent for Freight in April 2009, 1.70 percent for Passenger in April 2008, and 1.91 percent for the Combined TSI in April 2009. Changes in the Combined TSI tend to coincide with changes to the Freight TSI because Freight is its largest component. Averages over the last two years for percentage changes due to source data revision were an upward revision of 0.77 percent for Freight, an upward revision of 0.23 percent for Passenger, and an upward revision of 0.61 percent for the Combined TSI.
Table 1. Percentage Changes in the TSIs due to Revisions in the Source Data
| Date | Freight | Passenger | Combined |
|---|---|---|---|
| Sep-10 | 1.03 | 0.11 | 0.77 |
| Aug-10 | 0.87 | 0.12 | 0.65 |
| Jul-10 | 0.88 | 0.32 | 0.71 |
| Jun-10 | 0.70 | 0.36 | 0.58 |
| May-10 | 1.28 | 0.32 | 1.01 |
| Apr-10 | 1.18 | 0.33 | 0.94 |
| Mar-10 | 1.45 | 0.30 | 1.13 |
| Feb-10 | 1.83 | 0.35 | 1.43 |
| Jan-10 | 0.73 | 0.30 | 0.59 |
| Dec-09 | 1.12 | 0.20 | 0.86 |
| Nov-09 | 1.23 | 0.71 | 1.07 |
| Oct-09 | 1.46 | 0.14 | 1.10 |
| Sep-09 | 1.48 | 0.23 | 1.14 |
| Aug-09 | 1.41 | 0.10 | 1.05 |
| Jul-09 | 0.90 | -0.02 | 0.64 |
| Jun-09 | 0.68 | 0.17 | 0.53 |
| May-09 | 1.09 | 0.15 | 0.83 |
| Apr-09 | -2.62 | 0.22 | -1.91 |
| Mar-09 | 1.05 | 0.47 | 0.88 |
| Feb-09 | 1.31 | 0.33 | 1.04 |
| Jan-09 | -0.68 | -0.02 | -0.55 |
| Dec-08 | -0.09 | 0.37 | -0.01 |
| Nov-08 | 0.01 | -0.13 | -0.05 |
| Oct-08 | 0.23 | 0.17 | 0.18 |
| Summary October 2008-September 2010 | |||
| Average | 0.77 | 0.23 | 0.61 |
| Minimum | -2.62 | -0.13 | -1.91 |
| Date of Min | Apr-09 | Nov-08 | Apr-09 |
| Maximum | 1.83 | 0.71 | 1.43 |
| Date of Max | Feb-10 | Nov-09 | Feb-10 |
| Summary of Prior Years: | |||
| October 2005- September 2008 | |||
| Average | 0.07 | -0.09 | 0.00 |
| Minimum | -0.47 | -1.70 | -0.46 |
| Date of Min | Aug-06 | Apr-08 | Jul-08 |
| Maximum | 0.97 | 0.51 | 0.57 |
| Date of Max | Sep-08 | Aug-07 | Feb-07 |
| October 1990-September 2005 | |||
| Average | 0.15 | -0.10 | 0.08 |
| Minimum | -0.87 | -0.78 | -0.65 |
| Date of Min | Jun-03 | Apr-91 | Jun-03 |
| Maximum | 2.39 | 0.30 | 1.75 |
| Date of Max | Feb-91 | Dec-04 | Feb-91 |
Note: The first nine months of 1990 were excluded so that each group consists of 12-month years.
Source: Bureau of Transportation Statistics
Impact of Revisions to Weights and Methodology on the TSIs
The weights for the TSI are used to combine the output indexes of the nine component transportation services into aggregated indexes, namely the Freight TSI, the Passenger TSI and the Combined TSI. The weights for each service are based on the “adjusted” value-added[1] for the service and determine the relative importance of the individual modes that comprise each TSI. The relative importance of the individual modal freight services, from highest to lowest, was: Trucking, Rail, Aviation, Inland Water, Pipeline-Petroleum, and Pipeline-Liquefied Natural Gas. The relative importance of individual modal passenger services, also from highest to lowest, was: Aviation, Public Transit, and Rail Passenger. Freight comprises about three-fourths of the combined TSI, or about three times the weight of Passenger. The primary data sources for the TSI weights are the estimates of Gross Domestic Product (GDP) by industry produced by the Bureau of Economic Analysis (BEA). Weights are also estimated for splits of modal GDP among different services for aviation, rail, and pipelines (in particular, aviation freight service versus passenger service, railroad carload service versus intermodal service, and petroleum products versus natural gas). Revisions in weights are due to updates and revisions to the BEA and to revisions in the modal source data. Holding constant the component services, the TSI will tend to increase when the estimated weight of a faster-growing service increases, and vice versa.
Table 2 shows changes in the TSIs due to changes in weights/methodology tended to be small relative to changes due to source data revisions. There were no changes in any of the TSIs due to changes in weights/methodology of more than one percent up or down and virtually all changes were less than one-half percent. The largest upward changes due to changes in weights/methodology were 0.35 percent increase in the Freight TSI for May 2010, a 0.61 percent increase in the Passenger TSI for December 1993, and a 0.82 percent increase in the Combined TSI for April 2009. The largest downward changes due to changes in weights/methodology were a 0.45 percent decrease in the Freight TSI in January 2000, a 0.23 percent decrease in the Passenger TSI for July 2010 and a 0.27 percent decrease in the Combined TSI for February 1994.
Table 2. Percentage Changes in the TSIs due to Changes in Weights/Methodology
| Date | Freight | Passenger | Combined |
|---|---|---|---|
| Sep-10 | 0.32 | -0.19 | 0.63 |
| Aug-10 | 0.25 | -0.18 | 0.58 |
| Jul-10 | 0.18 | -0.23 | 0.49 |
| Jun-10 | 0.32 | -0.21 | 0.62 |
| May-10 | 0.35 | -0.20 | 0.61 |
| Apr-10 | 0.04 | -0.19 | 0.37 |
| Mar-10 | 0.15 | -0.20 | 0.45 |
| Feb-10 | 0.32 | -0.21 | 0.55 |
| Jan-10 | 0.11 | -0.17 | 0.51 |
| Dec-09 | 0.16 | -0.17 | 0.54 |
| Nov-09 | 0.26 | -0.14 | 0.63 |
| Oct-09 | -0.01 | -0.14 | 0.52 |
| Sep-09 | 0.11 | -0.15 | 0.58 |
| Aug-09 | 0.29 | -0.20 | 0.70 |
| Jul-09 | 0.21 | -0.14 | 0.70 |
| Jun-09 | 0.34 | -0.11 | 0.81 |
| May-09 | 0.14 | -0.07 | 0.69 |
| Apr-09 | 0.26 | -0.10 | 0.82 |
| Mar-09 | 0.11 | -0.02 | 0.65 |
| Feb-09 | 0.18 | -0.02 | 0.63 |
| Jan-09 | -0.08 | -0.05 | 0.49 |
| Dec-08 | -0.05 | -0.03 | 0.48 |
| Nov-08 | -0.08 | -0.02 | 0.36 |
| Oct-08 | -0.10 | -0.04 | 0.31 |
| Summary October 2008-September 2010 | |||
| Average | 0.16 | -0.13 | 0.57 |
| Minimum | -0.10 | -0.23 | 0.31 |
| Date of Min | Oct-08 | Jul-10 | Oct-08 |
| Maximum | 0.35 | -0.02 | 0.82 |
| Date of Max | May-10 | Feb-09 | Apr-09 |
| Summary of Prior Years: | |||
| October 2005- September 2008 | |||
| Average | 0.10 | -0.05 | 0.05 |
| Minimum | -0.31 | -0.14 | -0.01 |
| Date of Min | Jun-08 | May-08 | Jan-06 |
| Maximum | 0.06 | 0.05 | 0.56 |
| Date of Max | Mar-07 | May-07 | May-07 |
| October 1990-September 2005 | |||
| Average | -0.05 | -0.01 | -0.02 |
| Minimum | -0.45 | -0.06 | -0.27 |
| Date of Min | Jan-00 | May-05 | Feb-94 |
| Maximum | 0.04 | 0.61 | 0.15 |
| Date of Max | Jun-05 | Dec-93 | Sep-05 |
Note: The first nine months of 1990 were excluded so that each group consists of 12-month years.
Source: Bureau of Transportation Statistics
Impact of Changes in Seasonal Adjustment Factors on the TSIs
Changes in the TSIs due to changes in seasonal adjustment factors are caused by changes in the underlying source data and the addition of new data points for the 2011 Bi-annual Revision.
The impact of changes in the estimated factors is presented in Table 3. The greatest upward revisions due to changes in the estimated seasonal factors were: 0.22 percent for Freight in June, 0.28 percent for Passenger in January, and 0.12 percent for the Combined TSI in May. The greatest downward revisions were: 0.65 percent for Freight in February, 0.89 percent for Passenger in February, and 0.49 percent for the Combined TSI in October.
Table 3. Average Percentage Change in TSI due to Changes in Seasonal Factors by Month (1990-2010)
| Month | Freight | Passenger | Combined |
|---|---|---|---|
| January | 0.08 | 0.28 | -0.38 |
| February | -0.65 | -0.89 | 0.09 |
| March | -0.09 | -0.10 | -0.01 |
| April | -0.19 | -0.27 | 0.07 |
| May | -0.07 | -0.13 | 0.12 |
| June | 0.22 | 0.27 | 0.11 |
| July | 0.09 | 0.18 | -0.12 |
| August | 0.09 | 0.17 | -0.12 |
| September | -0.19 | -0.15 | -0.27 |
| October | -0.04 | 0.14 | -0.49 |
| November | -0.29 | -0.25 | -0.34 |
| December | -0.13 | 0.01 | -0.43 |
Note: The first nine months of 1990 were excluded so that each month is the average over the most recent 20 years.
Source: Bureau of Transportation Statistics
Impact of Changes in Source Data, Seasonal Adjustment Factors, and Weights/Methodology by Type of Service on the TSI.
The previous three tables are organized by the components of change while this section gives the components of change by type of transportation service. The organization in this section highlights the relative contributions of each component of change. The pattern is dissimilar across the two sub-indexes both with respect to time and the largest components of change. The Freight TSI had relatively large upward changes for the October 2008 to September 2010 period and these were predominantly associated with changes in source data. In contrast, the Passenger TSI was characterized by downward changes in the most recent years and these changes were smaller.
Table 4. Freight TSI - Percentage Changes Due to:
| Date | Changes in Source Data | Changes in Seasonal Factors | Changes in Weights/Methodology | All Changes |
|---|---|---|---|---|
| Sep-10 | 1.03 | -0.06 | 0.32 | 1.30 |
| Aug-10 | 0.87 | 0.18 | 0.25 | 1.30 |
| Jul-10 | 0.88 | 0.12 | 0.18 | 1.19 |
| Jun-10 | 0.70 | 0.32 | 0.32 | 1.34 |
| May-10 | 1.28 | -0.08 | 0.35 | 1.55 |
| Apr-10 | 1.18 | -0.34 | 0.04 | 0.87 |
| Mar-10 | 1.45 | -0.26 | 0.15 | 1.33 |
| Feb-10 | 1.83 | -0.72 | 0.32 | 1.42 |
| Jan-10 | 0.73 | -0.10 | 0.11 | 0.74 |
| Dec-09 | 1.12 | -0.13 | 0.16 | 1.15 |
| Nov-09 | 1.23 | 0.24 | 0.26 | 1.74 |
| Oct-09 | 1.46 | 0.15 | -0.01 | 1.60 |
| Sep-09 | 1.48 | -0.18 | 0.11 | 1.41 |
| Aug-09 | 1.41 | 0.37 | 0.29 | 2.08 |
| Jul-09 | 0.90 | 0.21 | 0.21 | 1.32 |
| Jun-09 | 0.68 | 0.53 | 0.34 | 1.55 |
| May-09 | 1.09 | -0.13 | 0.14 | 1.10 |
| Apr-09 | -2.62 | 3.20 | 0.26 | 0.76 |
| Mar-09 | 1.05 | -0.52 | 0.11 | 0.63 |
| Feb-09 | 1.31 | -0.51 | 0.18 | 0.98 |
| Jan-09 | -0.68 | -0.01 | -0.08 | -0.78 |
| Dec-08 | -0.09 | -0.76 | -0.05 | -0.90 |
| Nov-08 | 0.01 | -0.02 | -0.08 | -0.09 |
| Oct-08 | 0.23 | 0.04 | -0.10 | 0.17 |
| Summary October 2008-September 2010 | ||||
| Average | 0.77 | 0.06 | 0.16 | 0.99 |
| Minimum | -2.62 | -0.76 | -0.10 | -0.90 |
| Date of Min | Apr-09 | Dec-08 | Oct-08 | Dec-08 |
| Maximum | 1.83 | 3.20 | 0.35 | 2.08 |
| Date of Max | Feb-10 | Apr-09 | May-10 | Aug-09 |
| Prior Years: | ||||
| October 2005- September 2008 | ||||
| Average | 0.07 | -0.05 | 0.10 | 0.06 |
| Minimum | -0.47 | -1.02 | -0.31 | -0.90 |
| Date of Min | Aug-06 | Nov-06 | Jun-08 | May-06 |
| Maximum | 0.97 | 0.77 | 0.06 | 0.70 |
| Date of Max | Sep-08 | Jun-07 | Mar-07 | Sep-08 |
| October 1990-September 2005 | ||||
| Average | 0.15 | -0.08 | -0.05 | -0.06 |
| Minimum | -0.87 | -1.99 | -0.45 | -1.07 |
| Date of Min | Jun-03 | Feb-91 | Jan-00 | Jun-98 |
| Maximum | 2.39 | 1.02 | 0.04 | 1.43 |
| Date of Max | Feb-91 | Jan-99 | Jun-05 | Feb-98 |
Table 5. Passenger TSI - Percentage Changes Due to:
| Date | Changes in Source Data | Changes in Seasonal Factors | Changes in Weights/Methodology | All Changes |
|---|---|---|---|---|
| Sep-10 | 0.11 | -0.17 | -0.19 | -0.25 |
| Aug-10 | 0.12 | -0.19 | -0.18 | -0.25 |
| Jul-10 | 0.32 | -0.42 | -0.23 | -0.33 |
| Jun-10 | 0.36 | -0.31 | -0.21 | -0.16 |
| May-10 | 0.32 | -0.25 | -0.20 | -0.13 |
| Apr-10 | 0.33 | -0.17 | -0.19 | -0.04 |
| Mar-10 | 0.30 | -0.12 | -0.20 | -0.03 |
| Feb-10 | 0.35 | -0.10 | -0.21 | 0.04 |
| Jan-10 | 0.30 | -0.20 | -0.17 | -0.08 |
| Dec-09 | 0.20 | 0.06 | -0.17 | 0.09 |
| Nov-09 | 0.71 | -0.83 | -0.14 | -0.27 |
| Oct-09 | 0.14 | -0.72 | -0.14 | -0.72 |
| Sep-09 | 0.23 | -0.72 | -0.15 | -0.63 |
| Aug-09 | 0.10 | -0.18 | -0.20 | -0.28 |
| Jul-09 | -0.02 | -0.05 | -0.14 | -0.21 |
| Jun-09 | 0.17 | -0.48 | -0.11 | -0.41 |
| May-09 | 0.15 | -0.52 | -0.07 | -0.44 |
| Apr-09 | 0.22 | -0.02 | -0.10 | 0.11 |
| Mar-09 | 0.47 | -0.36 | -0.02 | 0.08 |
| Feb-09 | 0.33 | 0.31 | -0.02 | 0.62 |
| Jan-09 | -0.02 | -0.21 | -0.05 | -0.27 |
| Dec-08 | 0.37 | -0.32 | -0.03 | 0.01 |
| Nov-08 | -0.13 | -0.86 | -0.02 | -1.01 |
| Oct-08 | 0.17 | -1.28 | -0.04 | -1.16 |
| Summary October 2008-September 2010 | ||||
| Average | 0.23 | -0.34 | -0.13 | -0.24 |
| Minimum | -0.13 | -1.28 | -0.23 | -1.16 |
| Date of Min | Nov-08 | Oct-08 | Jul-10 | Oct-08 |
| Maximum | 0.71 | 0.31 | -0.02 | 0.62 |
| Date of Max | Nov-09 | Feb-09 | Feb-09 | Feb-09 |
| Prior Years: | ||||
| October 2005- September 2008 | ||||
| Average | -0.09 | -0.17 | -0.05 | -0.18 |
| Minimum | -1.70 | -1.41 | -0.14 | -1.75 |
| Date of Min | Apr-08 | Oct-07 | May-08 | Sep-08 |
| Maximum | 0.51 | 1.48 | 0.05 | 1.37 |
| Date of Max | Aug-07 | Feb-08 | May-07 | Feb-08 |
| October 1990-September 2005 | ||||
| Average | -0.10 | -0.12 | -0.01 | -0.08 |
| Minimum | -0.78 | -2.28 | -0.06 | -2.28 |
| Date of Min | Apr-91 | Dec-00 | May-05 | Dec-00 |
| Maximum | 0.30 | 2.03 | 0.61 | 1.89 |
| Date of Max | Dec-04 | Feb-04 | Dec-93 | Feb-04 |
Table 6. Combined TSI - Percentage Changes Due to:
| Date | Changes in Source Data | Changes in Seasonal Factors | Changes in Weights/Methodology | All Changes |
|---|---|---|---|---|
| Sep-10 | 0.77 | -0.09 | 0.63 | 1.31 |
| Aug-10 | 0.65 | 0.08 | 0.58 | 1.31 |
| Jul-10 | 0.71 | -0.02 | 0.49 | 1.19 |
| Jun-10 | 0.58 | 0.15 | 0.62 | 1.36 |
| May-10 | 1.01 | -0.14 | 0.61 | 1.49 |
| Apr-10 | 0.94 | -0.31 | 0.37 | 1.00 |
| Mar-10 | 1.13 | -0.24 | 0.45 | 1.34 |
| Feb-10 | 1.43 | -0.58 | 0.55 | 1.39 |
| Jan-10 | 0.59 | -0.14 | 0.51 | 0.96 |
| Dec-09 | 0.86 | -0.09 | 0.54 | 1.31 |
| Nov-09 | 1.07 | -0.03 | 0.63 | 1.68 |
| Oct-09 | 1.10 | -0.08 | 0.52 | 1.54 |
| Sep-09 | 1.14 | -0.33 | 0.58 | 1.39 |
| Aug-09 | 1.05 | 0.22 | 0.70 | 1.99 |
| Jul-09 | 0.64 | 0.13 | 0.70 | 1.48 |
| Jun-09 | 0.53 | 0.26 | 0.81 | 1.60 |
| May-09 | 0.83 | -0.24 | 0.69 | 1.27 |
| Apr-09 | -1.91 | 2.34 | 0.82 | 1.21 |
| Mar-09 | 0.88 | -0.49 | 0.65 | 1.03 |
| Feb-09 | 1.04 | -0.32 | 0.63 | 1.35 |
| Jan-09 | -0.55 | -0.07 | 0.49 | -0.13 |
| Dec-08 | -0.01 | -0.66 | 0.48 | -0.19 |
| Nov-08 | -0.05 | -0.24 | 0.36 | 0.07 |
| Oct-08 | 0.18 | -0.29 | 0.31 | 0.20 |
| Summary October 2008-September 2010 | ||||
| Average | 0.61 | -0.05 | 0.57 | 1.13 |
| Minimum | -1.91 | -0.66 | 0.31 | -0.19 |
| Date of Min | Apr-09 | Dec-08 | Oct-08 | Dec-08 |
| Maximum | 1.43 | 2.34 | 0.82 | 1.99 |
| Date of Max | Feb-10 | Apr-09 | Apr-09 | Aug-09 |
| Prior Years: | ||||
| October 2005- September 2008 | ||||
| Average | 0.00 | -0.09 | 0.05 | -0.06 |
| Minimum | -0.46 | -0.90 | -0.01 | -0.50 |
| Date of Min | Jul-08 | Nov-06 | Jan-06 | May-06 |
| Maximum | 0.57 | 0.67 | 0.56 | 0.87 |
| Date of Max | Feb-07 | Jun-07 | May-07 | Feb-08 |
| October 1990-September 2005 | ||||
| Average | 0.08 | -0.11 | -0.02 | -0.07 |
| Minimum | -0.65 | -1.64 | -0.27 | -0.78 |
| Date of Min | Jun-03 | Feb-91 | Feb-94 | Jun-98 |
| Maximum | 1.75 | 0.64 | 0.15 | 0.97 |
| Date of Max | Feb-91 | Sep-01 | Sep-05 | Feb-98 |
Note: The first nine months of 1990 were excluded so that each group consists of 12-month years.
Source: Bureau of Transportation Statistics
Appendix
Summary of Changes to the TSIs Between the Initial Release and the Four-Month Revision.
The changes in the TSIs that occur with the 4-month revision are identified in the monthly TSI press release and are summarized here. In addition to the percentage change in the index numbers, the revision to the percentage growth rates are also given. Growth rates give the relative increases or decreases, which are the most used feature of index numbers. While in general the revisions to the growth rates are smaller than the revisions to the index numbers, as indicated by the average revision, this need not be the case when the index is revised in opposite directions in consecutive months. Another phenomenon worth mentioning is that the size of the 4-month revision tends to increase as time elapses since the last comprehensive revision. This is because more changes to source data will take place as time goes on and consequently so will the cumulative effect of changes to source data, particularly if changes to source data have the same direction (either positive revisions or negative revisions). Note that the 2009 Bi-Annual Revision was implemented with the June 2009 release and included data through May 2009. Right before the 2009 Bi-Annual Revision, the sizes of the 4-month revisions were significant. The size of the 4-month revision was considerably reduced following the Annual Revision. However, it increased again as time elapsed from the Bi-Annual Revision. This phenomenon highlights the necessity of these comprehensive revisions.
Table 7. Percentage Change Between the Initial Release and the Four-Month Revision, October 2008 to September 2010
| Date | Freight TSI | Passenger TSI | Combined TSI | |||
|---|---|---|---|---|---|---|
| % Revision to Index | Revision to % Growth Rate | % Revision to Index | Revision to % Growth Rate | % Revision to Index | Revision to % Growth Rate | |
| Sep-10 | 5.04 | 0.01 | 1.26 | 0.06 | 4.09 | 0.02 |
| Aug-10 | 5.04 | 0.12 | 1.20 | -0.17 | 4.07 | 0.05 |
| Jul-10 | 4.91 | 0.06 | 1.37 | 0.00 | 4.02 | 0.04 |
| Jun-10 | 4.85 | -0.17 | 1.37 | 0.91 | 3.98 | 0.09 |
| May-10 | 5.03 | 0.26 | 0.46 | -1.09 | 3.88 | -0.06 |
| Apr-10 | 4.75 | 0.21 | 1.55 | 0.35 | 3.95 | 0.25 |
| Mar-10 | 4.53 | 0.45 | 1.19 | 0.81 | 3.69 | 0.53 |
| Feb-10 | 4.07 | 0.12 | 0.40 | -0.72 | 3.15 | -0.08 |
| Jan-10 | 3.94 | 0.45 | 1.14 | -0.40 | 3.24 | 0.25 |
| Dec-09 | 3.47 | 1.19 | 1.54 | 0.35 | 2.98 | 0.98 |
| Nov-09 | 2.25 | 0.91 | 1.19 | 0.85 | 1.98 | 0.89 |
| Oct-09 | 1.35 | 0.36 | 0.32 | 0.26 | 1.09 | 0.33 |
| Sep-09 | 0.98 | 0.61 | 0.06 | 0.59 | 0.75 | 0.61 |
| Aug-09 | 0.36 | 0.06 | -0.53 | -0.75 | 0.14 | -0.15 |
| Jul-09 | 0.31 | 0.23 | 0.23 | 0.06 | 0.28 | 0.19 |
| Jun-09 | 0.08 | 0.60 | 0.16 | 0.77 | 0.09 | 0.64 |
| May-09 | -0.52 | 6.09 | -0.61 | 2.20 | -0.54 | 5.07 |
| Apr-09 | -6.58 | -0.58 | -2.82 | -0.09 | -5.60 | -0.47 |
| Mar-09 | -6.02 | -0.36 | -2.73 | 0.17 | -5.15 | -0.23 |
| Feb-09 | -5.68 | -0.97 | -2.90 | -0.55 | -4.93 | -0.85 |
| Jan-09 | -4.77 | -1.26 | -2.36 | -1.47 | -4.12 | -1.22 |
| Dec-08 | -3.53 | -0.53 | -0.90 | 0.43 | -2.91 | -0.31 |
| Nov-08 | -3.00 | -0.75 | -1.33 | -1.88 | -2.60 | -1.03 |
| Oct-08 | -2.26 | -1.34 | 0.57 | -0.66 | -1.58 | -1.17 |
| Summary | ||||||
| Average | 0.78 | 0.24 | -0.01 | 0.00 | 0.58 | 0.18 |
| Minimum | -6.58 | -1.34 | -2.90 | -1.88 | -5.60 | -1.22 |
| Date of Min | Apr-09 | Oct-08 | Feb-09 | Nov-08 | Apr-09 | Jan-09 |
| Maximum | 5.04 | 6.09 | 1.55 | 2.20 | 4.09 | 5.07 |
| Date of Max | Sep-10 | May-09 | Apr-10 | May-09 | Sep-10 | May-09 |
[1] Adjusted value-added for each service is calculated for each year by dividing nominal value-added by the average of the TSI quantity index for the year.