You are here

The 2009 TSI Bi-annual Revision

The 2009 TSI Bi-annual Revision

The 2009 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 2007 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

The 2009 Bi-annual Revision includes two methodological changes and one change in the source data. The first methodological change is the modification of the models used to seasonally adjust individual modal series as a result of our on-gong efforts to improve the seasonal adjustment process. Documentation for the current seasonal adjustment models can be found at http://www.bts.gov/programs/economics_and_finance/transportation_services_index/methodology/. The second methodological change and the change in the source data are both in regard to petroleum pipeline services: Alaskan production of crude oil has been added to petroleum pipeline services and an unnecessary daily-to-monthly conversion of petroleum pipeline services has been eliminated. Previously, petroleum pipeline services were measured by monthly PADD (Petroleum Administration for Defense Districts) to PADD movements among the five PADD districts in the United States. Alaskan production1, takes place on the North Slope of Alaska and is then transported via the Trans-Alaska (a.k.a. Alyeksa) pipeline to the port of Valdez where it is loaded onto tankers2. The services provided by Trans-Alaska are a major component of all U.S. petroleum pipeline services but were not captured in our previous measure because all the movement was within PADD 5. The addition of Trans-Alaska petroleum pipeline is done to better achieve our goal of measuring all U.S. commercial transportation services.

Methodological or Source Data Changes to the TSI

Excel | CSV

Year of Implementation Change
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 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 2008 were initially released in February 2009 and were revised with the June 2009 release of the TSI (Original) and then were revised again with the July 2009 Bi-annual revision (Final). The analysis in this section with respect to the December 2008 TSIs refers to changes to the December 2008 TSIs from the June 2009 release.

The basic model for analysis is given below:

Let t = 1,.., 228 index the months between January, 1990 and December 2008.

Let uppercase t superscirpt{0} subscript{lowercase t}  be the TSI index published in June 2009, without the Bi-annual Revision.

Let uppercase t superscript {uppercase a uppercase r} subscript {lowercase t}  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 uppercase t superscirpt{0} subscript{lowercase t}in the monthly releases following the 4-month but before the annual revision.)

Let uppercase t superscript {uppercase f uppercase s uppercase d} subscript {lowercase t}  be the TSI index compiled using the final source data, but the same seasonal factors and weights/methodology as in uppercase t superscirpt{0} subscript{lowercase t}.

Let uppercase t superscript {uppercase f uppercase s  uppercase f} subscript {lowercase t}  be the TSI index compiled using both the final source data and the final seasonal factors, but the weights/methodology as in uppercase t superscirpt{0} subscript{lowercase t}.

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:

lowercase delta subscript {lowercase t} is equal to uppercase t superscript {uppercase f uppercase s uppercase d} subscript {lowercase t} over uppercase t superscript {0} subscript {lowercase t}

lowercase psi subscript {lowercase t} is equal to uppercase t superscript {uppercase f uppercase s uppercase f} subscript {lowercase t} over uppercase t superscript {uppercase f uppercase s uppercase d} subscript {lowercase t}

lowercase omega subscript {lowercase t} is equal to uppercase t superscript {uppercase a uppercase r} subscript {lowercase t} over uppercase t superscript {uppercase f uppercase s uppercase f} subscript {lowercase t}

uppercase t superscript {uppercase a uppercase r} subscript {lowercase t} is equal to lowercase delta subscript {lowercase t} dot lowercase psi subscript {lowercase t} dot lowercase omega subscript {lowercase t} dot uppercase t superscript {0} subscript {lowercase t}

 

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: 1.19 percent for Freight in March 2008, 3.23 percent for Passenger in May 2007, and 0.88 percent for the combined TSI in July 1993. The largest downward revisions were: 1.48 percent for Freight in July 1990, 1.40 percent for Passenger in March 2008, and 1.11 percent for the Combined TSI in July 1990. The large upward revision for the Passenger TSI in May 2007 was part of a substantial historical revision for the last two years of data for one of the component modes. Averages over the last two years for percentage changes due to source data revision were a downward revision of 0.16 percent for Freight, an upward revision of 0.16 percent for Passenger, and a downward revision of 0.08 percent for the combined TSI.

Table 1. Percentage Changes in the TSIs due to Revisions in the Source Data

Excel | CSV

Date Freight Passenger Combined
Dec-08 -0.98 -0.57 -0.87
Nov-08 -1.00 -0.56 -0.89
Oct-08 -0.61 -0.52 -0.58
Sep-08 -0.61 -0.16 -0.50
Aug-08 -0.79 -0.19 -0.64
Jul-08 -0.82 -0.25 -0.67
Jun-08 -0.30 -0.34 -0.30
May-08 0.06 -0.15 0.02
Apr-08 0.50 -0.05 0.37
Mar-08 1.19 -1.40 0.56
Feb-08 -0.48 -1.34 -0.68
Jan-08 0.16 -0.61 -0.03
Dec-07 1.13 -0.13 0.83
Nov-07 -0.11 -0.52 -0.21
Oct-07 -0.21 -0.55 -0.29
Sep-07 -0.23 1.44 0.19
Aug-07 -0.42 1.14 -0.03
Jul-07 -0.23 1.32 0.15
Jun-07 -0.01 0.89 0.21
May-07 -0.13 3.23 0.69
Apr-07 -0.01 1.04 0.24
Mar-07 -0.18 1.25 0.16
Feb-07 0.20 0.73 0.32
Jan-07 0.12 0.02 0.10
Summary January 2005-December 2006      
Average -0.16 0.16 -0.08
Minimum -1.00 -1.40 -0.89
Date of Min Nov-08 Mar-08 Nov-08
Maximum 1.19 3.23 0.83
Date of Max Mar-08 May-07 Dec-07
Summary of Prior Years:      
January 2002-December 2004      
Average -0.09 -0.09 -0.09
Minimum -0.75 -0.79 -0.55
Date of Min Jul-06 Jan-06 Jul-06
Maximum 0.90 0.19 0.52
Date of Max Sep-06 May-06 Sep-06
January 1990-December 2003      
Average 0.01 0.00 0.00
Minimum -1.48 0.00 -1.11
Date of Min Jul-90 Aug-03 Jul-90
Maximum 1.16 0.00 0.88
Date of Max Jul-93 Dec-96 Jul-93

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-added3 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. 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 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 weights/methodology tended to move the TSI upward in the most recent years, and downward in the earlier years with positive average revisions for all three indexes in both the 2004-2006 and 2007-2008 periods and negative average revisions for all three indexes for the 1990-2003 period.

Table 2. Percentage Changes in the TSIs due to Changes in Weights/Methodology

Excel | CSV

Date Freight Passenger Combined
Dec-08 -0.87 -0.98 -0.57
Nov-08 -0.89 -1.00 -0.56
Oct-08 -0.58 -0.61 -0.52
Sep-08 -0.50 -0.61 -0.16
Aug-08 -0.64 -0.79 -0.19
Jul-08 -0.67 -0.82 -0.25
Jun-08 -0.30 -0.30 -0.34
May-08 0.02 0.06 -0.15
Apr-08 0.37 0.50 -0.05
Mar-08 0.56 1.19 -1.40
Feb-08 -0.68 -0.48 -1.34
Jan-08 -0.03 0.16 -0.61
Dec-07 0.83 1.13 -0.13
Nov-07 -0.21 -0.11 -0.52
Oct-07 -0.29 -0.21 -0.55
Sep-07 0.19 -0.23 1.44
Aug-07 -0.03 -0.42 1.14
Jul-07 0.15 -0.23 1.32
Jun-07 0.21 -0.01 0.89
May-07 0.69 -0.13 3.23
Apr-07 0.24 -0.01 1.04
Mar-07 0.16 -0.18 1.25
Feb-07 0.32 0.20 0.73
Jan-07 0.10 0.12 0.02
Summary January 2007-December 2008      
Average -0.08 -0.16 0.16
Minimum -0.89 -1.00 -1.40
Date of Min Nov-08 Nov-08 Mar-08
Maximum 0.83 1.19 3.23
Date of Max Jul-93 Jul-93 Dec-96
Summary of Prior Years:      
January 2004-December 2006      
Average -0.09 -0.09 -0.09
Minimum -0.55 -0.75 -0.79
Date of Min Jul-06 Jul-06 Jan-06
Maximum 0.52 0.90 0.19
Date of Max Sep-06 Sep-06 May-06
January 1990-December 2003      
Average 0.00 0.01 0.00
Minimum -1.11 -1.48 0.00
Date of Min Jul-90 Jul-90 Aug-03
Maximum 0.88 1.16 0.00
Date of Max Jul-93 Jul-93 Dec-96

Source: Bureau of Transportation Statistics

Impact of Changes in Seasonal Adjustment Factors on the TSIs

The 2009 Bi-annual Revision incorporates changes in both the methodology for estimating seasonal adjustment factors and the effects on estimated seasonal factors due to revisions in the source data4.

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: 0.15 percent for Freight in May, August and December, 0.32 percent for Passenger in November, and 0.17 percent for the Combined TSI in December. The greatest downward revisions were: 0.41 percent for Freight in November, 0.22 percent for Passenger in June, and 0.22 percent for the Combined TSI in November.

Table 3. Average Percentage Change in TSI due to Changes in Seasonal Factors by Month (1990-2008)

Excel | CSV

Month Freight Passenger Combined
January 0.12 0.11 0.12
February -0.06 0.17 0.00
March 0.07 -0.06 0.04
April 0.00 -0.11 -0.03
May 0.15 -0.21 0.06
June 0.10 -0.22 0.02
July -0.07 -0.06 -0.07
August 0.15 -0.02 0.10
September -0.04 0.09 0.00
October 0.03 0.19 0.07
November -0.41 0.32 -0.22
December 0.15 0.23 0.17

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 changes in the earliest years, predominantly associated with changes in source data. In contrast, changes in the Passenger TSI were concentrated in the most recent years and are primarily caused by changes in source data and changes in seasonal factors while changes in weights/methodology had less impact.

Table 4. Freight TSI - Percentage Changes Due to:

Excel | CSV

Date Changes in Source Data Changes in Seasonal Factors Changes in Weights/ Methodology All Changes
Dec-08 -0.98 -0.02 0.22 -0.78
Nov-08 -1.00 0.00 0.23 -0.78
Oct-08 -0.61 -0.31 0.30 -0.62
Sep-08 -0.61 -0.01 0.30 -0.33
Aug-08 -0.79 0.04 0.40 -0.34
Jul-08 -0.82 0.07 0.41 -0.34
Jun-08 -0.30 0.18 0.06 -0.06
May-08 0.06 0.43 -0.01 0.48
Apr-08 0.50 0.44 -0.17 0.77
Mar-08 1.19 0.31 -0.29 1.21
Feb-08 -0.48 0.33 0.75 0.60
Jan-08 0.16 0.67 -0.07 0.76
Dec-07 1.13 0.24 0.23 1.60
Nov-07 -0.11 -0.17 0.41 0.13
Oct-07 -0.21 -0.27 0.23 -0.26
Sep-07 -0.23 -0.30 0.26 -0.26
Aug-07 -0.42 -0.06 0.12 -0.36
Jul-07 -0.23 -0.41 0.00 -0.63
Jun-07 -0.01 -0.24 0.06 -0.20
May-07 -0.13 0.16 0.00 0.04
Apr-07 -0.01 0.28 0.11 0.38
Mar-07 -0.18 0.68 0.50 1.00
Feb-07 0.20 -0.45 0.05 -0.20
Jan-07 0.12 0.03 0.06 0.21
January 2007-December 2008        
Average -0.16 0.07 0.17 0.08
Minimum -1.00 -0.45 -0.29 -0.78
Date of Min Nov-08 Feb-07 Mar-08 Dec-08
Maximum 1.19 0.68 0.75 1.60
Date of Max Mar-08 Mar-07 Feb-08 Dec-07
Prior Years:        
January 2004-December 2006        
Average -0.09 0.01 0.08 0.00
Minimum -0.75 -0.45 -0.11 -0.68
Date of Min Jul-06 Feb-04 Jan-06 Jun-06
Maximum 0.90 0.26 0.37 1.44
Date of Max Sep-06 Sep-06 Mar-06 Sep-06
January 1990-December 2003        
Average 0.01 0.01 -0.36 -0.34
Minimum -1.48 -0.79 -1.17 -2.31
Date of Min Jul-90 Feb-90 Apr-91 Jul-90
Maximum 1.16 0.39 0.33 0.78
Date of Max Jul-93 Aug-92 Aug-01 Jul-93

Source: Bureau of Transportation Statistics

Table 5. Passenger TSI - Percentage Changes Due to:

Excel | CSV

Date Changes in Source Data Changes in Seasonal Factors Changes in Weights/ Methodology All Changes
Dec-08 -0.57 -0.42 0.34 -0.65
Nov-08 -0.56 0.02 -0.12 -0.65
Oct-08 -0.52 -0.33 0.14 -0.71
Sep-08 -0.16 -0.51 0.02 -0.64
Aug-08 -0.19 -0.33 0.07 -0.45
Jul-08 -0.25 -0.52 0.08 -0.69
Jun-08 -0.34 -0.24 0.00 -0.57
May-08 -0.15 -0.16 0.00 -0.31
Apr-08 -0.05 0.32 -0.11 0.16
Mar-08 -1.40 1.24 0.69 0.50
Feb-08 -1.34 1.68 0.91 1.23
Jan-08 -0.61 1.42 0.35 1.14
Dec-07 -0.13 1.01 0.32 1.20
Nov-07 -0.52 1.25 0.02 0.73
Oct-07 -0.55 0.26 0.19 -0.10
Sep-07 1.44 -0.21 0.06 1.30
Aug-07 1.14 -1.24 0.07 -0.04
Jul-07 1.32 -1.32 0.04 0.02
Jun-07 0.89 -0.66 -0.05 0.18
May-07 3.23 -0.83 -0.19 2.17
Apr-07 1.04 0.30 -0.33 1.01
Mar-07 1.25 0.91 -0.51 1.65
Feb-07 0.73 1.54 -0.09 2.18
Jan-07 0.02 0.94 0.00 0.96
January 2007-December 2008        
Average 0.16 0.17 0.08 0.40
Minimum -1.40 -1.32 -0.51 -0.71
Date of Min Mar-08 Jul-07 Mar-07 Oct-08
Maximum 3.23 1.68 0.91 2.18
Date of Max May-07 Feb-08 Feb-08 Feb-07
Prior Years:        
January 2004-December 2006        
Average -0.09 -0.01 0.02 -0.08
Minimum -0.79 -1.28 -0.20 -1.46
Date of Min Jan-06 Aug-06 Apr-06 Aug-06
Maximum 0.19 1.27 0.22 0.74
Date of Max May-06 Feb-06 Dec-05 Dec-06
January 1990-December 2003        
Average 0.00 0.02 -0.01 0.02
Minimum 0.00 -0.25 -0.10 -0.34
Date of Min Aug-03 Jul-91 Jul-92 Jul-91
Maximum 0.00 0.42 0.21 0.36
Date of Max Dec-96 May-92 Dec-93 Dec-03

Source: Bureau of Transportation Statistics

Table 6. Combined TSI - Percentage Changes Due to:

Excel | CSV

Date Changes in Source Data Changes in Seasonal Factors Changes in Weights/ Methodology All Changes
Dec-08 -0.87 -0.12 0.35 -0.64
Nov-08 -0.89 0.01 0.24 -0.64
Oct-08 -0.58 -0.32 0.36 -0.54
Sep-08 -0.50 -0.14 0.33 -0.31
Aug-08 -0.64 -0.05 0.42 -0.27
Jul-08 -0.67 -0.08 0.44 -0.32
Jun-08 -0.30 0.08 0.15 -0.08
May-08 0.02 0.28 0.09 0.39
Apr-08 0.37 0.41 -0.05 0.73
Mar-08 0.56 0.53 0.05 1.14
Feb-08 -0.68 0.65 0.90 0.86
Jan-08 -0.03 0.85 0.13 0.96
Dec-07 0.83 0.43 0.35 1.61
Nov-07 -0.21 0.17 0.42 0.38
Oct-07 -0.29 -0.14 0.33 -0.11
Sep-07 0.19 -0.27 0.32 0.23
Aug-07 -0.03 -0.36 0.21 -0.18
Jul-07 0.15 -0.64 0.12 -0.37
Jun-07 0.21 -0.35 0.13 0.00
May-07 0.69 -0.09 0.06 0.67
Apr-07 0.24 0.28 0.10 0.62
Mar-07 0.16 0.74 0.35 1.25
Feb-07 0.32 0.02 0.11 0.46
Jan-07 0.10 0.25 0.14 0.49
January 2007-December 2008        
Average -0.08 0.09 0.25 0.26
Minimum -0.89 -0.64 -0.05 -0.64
Date of Min Nov-08 Jul-07 Apr-08 Dec-08
Maximum 0.83 0.85 0.90 1.61
Date of Max Dec-07 Jan-08 Feb-08 Dec-07
Prior Years:        
January 2004-December 2006        
Average -0.09 0.00 0.09 0.01
Minimum -0.55 -0.28 -0.07 -0.62
Date of Min Jul-06 Aug-06 Nov-05 Aug-06
Maximum 0.52 0.28 0.29 0.84
Date of Max Sep-06 Dec-06 Mar-06 Sep-06
January 1990-December 2003        
Average 0.00 0.02 -0.25 -0.24
Minimum -1.11 -0.56 -0.85 -1.74
Date of Min Jul-90 Feb-90 Apr-91 Jul-90
Maximum 0.88 0.32 0.24 0.59
Date of Max Jul-93 May-93 Aug-01 Jul-93

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 lower 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. Note that there is a clear pattern to the revisions to the Freight TSI with larger downward revisions in the most recent months. In contrast, revisions to the Passenger TSI have been positive on average and the size of the revisions is more uniformly distributed over the 24 months.

Table 7. Percentage Changes between Initial Release and the Four-Month Revision, 1/2007-12/2008

Excel | CSV

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
Dec-08 -3.53 -0.53 -0.90 0.43 -2.91 -1.37
Nov-08 -3.00 -0.75 -1.33 -1.88 -2.60 -1.90
Oct-08 -2.26 -1.34 0.57 -0.66 -1.58 0.04
Sep-08 -0.94 0.88 1.23 1.18 -0.42 0.26
Aug-08 -1.83 -0.39 0.04 -1.68 -1.39 -2.41
Jul-08 -1.44 0.13 1.74 0.53 -0.68 1.53
Jun-08 -1.56 -0.24 1.20 -0.04 -0.90 -0.10
May-08 -1.33 -1.46 1.24 -0.51 -0.72 -0.28
Apr-08 0.10 1.13 1.76 0.69 0.50 0.99
Mar-08 -1.01 -1.05 1.07 -1.07 -0.51 -3.86
Feb-08 0.06 0.07 2.14 0.67 0.55 1.12
Jan-08 -0.01 0.40 1.45 1.29 0.34 3.52
Dec-07 -0.40 -0.44 0.14 -1.10 -0.28 -2.93
Nov-07 0.04 -0.28 1.24 -0.61 0.32 0.78
Oct-07 0.32 0.43 1.86 1.65 0.69 2.42
Sep-07 -0.10 -0.20 0.20 -1.84 -0.04 -2.51
Aug-07 0.10 0.17 2.04 0.87 0.57 0.45
Jul-07 -0.07 0.42 1.16 -0.20 0.23 -0.11
Jun-07 -0.49 -0.01 1.36 0.54 -0.04 0.14
May-07 -0.48 -0.63 0.81 1.40 -0.17 0.11
Apr-07 0.15 -0.48 -0.58 -0.90 -0.09 -1.57
Mar-07 0.63 -0.18 0.31 -0.36 -0.43 -1.15
Feb-07 0.80 0.25 0.67 -1.67 -0.20 -0.13
Jan-07 0.55 0.44 2.38 0.77 0.01 0.83
Summary            
Average -0.66 -0.15 0.91 -0.10 -0.41 -0.26
Minimum -3.53 -1.46 -1.33 -1.88 -2.91 -3.86
Date of Min Dec-08 May-08 Nov-08 Nov-08 Dec-08 Mar-08
Maximum 0.80 1.13 2.38 1.65 0.69 3.52
Date of Max Feb-07 Apr-08 Jan-07 Oct-07 Oct-07 Jan-08

Source: Bureau of Transportation Statistics

1 Data is available at http://tonto.eia.doe.gov/dnav/pet/pet_sum_crdsnd_adc_mbbl_m.htm, which also includes a link to definitions and maps of PADDs. See also the original source documentation for the TSI at http://www.bts.gov/programs/economics_and_finance/transportation_services_index/html/source_and_documentation_and_data_quality.html.

2See the U.S. Energy Information Agency’s state profile for Alaska at http://tonto.eia.doe.gov/state/state_energy_profiles.cfm?sid=AK .

3 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.

4 Note that when the source data is held constant, there will be an inverse relationship between changes in the estimated seasonal patterns and the impact on the TSIs because seasonal adjustment reduces (increases) actual output the most for months that are estimated to be the most (least) important for annual output.