U . S . INTRA-INDUSTRY TRADE IN AIR TRANSPORT SERVICES : MEASUREMENT AND RESULTS Summary

The paper deals with the measurement of intra-industry trade (IIT) in air transport services and it ́s components (passenger and air cargo services) among the United States of America and 31 chosen countries in time period 2000 2011. For the purpose of analysis, we used traditional and alternative methods of IIT measurements. Results of the analysis confirm the existence of IIT in air transport services and it ́s components (passenger and air cargo services between The United States of America and 31 chosen countries in time period 2000 – 2011. On the other hand, we are unable to determine the trend of IIT in air transport services between The United States of America and 31 chosen countries in time period 2000 – 2011because of fluctuating turnover values.


INTRODUCTION
Since 1960 economists deal with the measurement of intra-industry trade (IIT).Table 1 shows a summary of selected studies addressing to a measurement of IIT in goods.As it can be seen, the mentioned studies dealing with a research of IIT in goods used an alternative ways of measuring.

Table 1
The overview of selected studies on intra-industry trade in goods Table 2 shows an overview of studies involved in research and measurement of international intraindustry trade in services.As it can be seen, the research of IIT has used as a basic metric measurement the Grubel-Lloyd index and marginal Grubel-Lloyd index.None of the studies deals with the IIT in air transport services and it´s components.

OBJECTIVES AND METHODOLOGY
The aim of this paper is to measure the intra-industry component of international trade in air transport services.Determinants analysed in previous studies formed the basis of our research.We have developed a proposal for measuring the intra-industry trade in air transport services based on previous analysis that aimed to measure the intensity; scale and progress of international intra-industry trade in goods and services.According to the literature research we performed this technique has not yet been applied to measure the intensity, scale and progress of international trade in air transport services.Given the fact that the provided data by International Trade Centre (ITC, 2014) is incomplete, we analysed IIT in air transport services and it´s components between the United States and 311 selected countries, whose exports of air transport services amounted in 2011 to more than 73% of world exports of air transport services and import of air transport services amounted in 2011 to more than 72% of world air transport services import.Brülhart (2002) divided measuring methods of IIT into three groups, namely static, quasi-dynamic and dynamic methods.Table 3 shows traditional and alternative measurement methods.Some of them we applied on IIT in air transport services.

Grubel-Lloyd index
To determine the intensity of intra-industry component of international trade we used a traditional (static) Grubel-Lloyd index (GLI) considered as a standard tool to measure intra-industry trade in goods and services (Shelburne, Gonzales, 2004).GLI is a static measure of IIT at one time point.
where: GLj -Grubel-Lloyd index; Xij -export of country j in sector i; Mij -import to county j in sector i

Marginal Grubel-Lloyd index
This index deals with the changes in trade at the time and counts with a negative numberschanges tend to be negative numbers.Coefficient assumes values in the interval < 0 ; 1 >.The closer to the value 1, the more intra-industry character of trade change.
where: MGLj -Marginal Grubel-Lloyd index; ΔXij -change in export in sector i between two points in time; ΔMij -change in import in sector i between two points in time

Greenaway-Hine-Milner-Elliot method
Greenaway et al. (1994) have proposed a measurement that is different from the Grubel-Lloyd index.Sit indicates the absolute value and not proportional.Greenaway-Hine-Milner-Elliot (GHME) static method determines the turnover of IIT at the time and quasi-dynamic type of GHME method indicates the annual change IIT turnover.
where: GHME -Greenaway-Hine-Milner-Elliot method; Xij -export of country j in sector I; Mijimport to county j in sector i For the purpose of the analysis, we applied three abovementioned measurement methods on IIT in air transport services between the United States and 31 chosen countries between 2000 and 2011.
According to the ITC database, availability of the data is quite different in case of air transport services as a whole, air cargo services and passenger traffic as can be seen in Figure 1.Many economists are dealing with the problem of services data availability and reporting.Because the services classification isn´t uniform in every country, provided data by the countries may be not compatible and comparable with other countries and services sectors.83 out of 372 analysed cases couldn´t be analysed due to the data unavailability in case of international trade in air transport services between the United States and 31 chosen countries between 2000 and 2011, 150 and 156 out of 372 analysed cases couldn´t be also analysed due to data unavailability from the passenger air transport services sector and air cargo services sector.

RESULTS AND DISCUSSION
For the purpose of this paper, we are presenting results of the three applied methods -Grubel-Lloyd index, Marginal Grubel-Lloyd index and Greenaway-Hine-Milner-Elliot method.We are still analysing the results of the other used methods and are not published yet.

Grubel-Lloyd Index
From 289 measures, 60 values were greater than 0,9 which means high intra-industry intensity of international trade in air transport services.Grubel-Lloyd index equal to the value 1 in three cases between the United States and Slovenia, Latvia and Denmark which means perfect intra-industry trade in air transport services.Zero values were measured in four cases, which means that trade between chosen countries has inter-industry character.
From 222 measures, 10 values were greater than 0,9 which means high intra-industry intensity of international trade in passenger air transport services.Grubel-Lloyd index equal to the value 1 in 2010 between the United States and Cyprus which means perfect intra-industry trade in passenger air transport services.Zero values were measured in 27 cases, which means that trade between chosen countries has inter-industry character.
From 216 measures, 37 values were greater than 0,9 which means high intra-industry intensity of international trade in air cargo services.Grubel-Lloyd index equal to the value 1 in two (Latvia and Poland), which means perfect intra-industry trade in air cargo services.Zero values were measured in 30 cases, which means that trade between chosen countries has inter-industry character.The largest intra-industry intensity was reflected in air transport services as a whole between the United States and 31 chosen countries in the period from 2000 to 2011.On the other hand the weakest intensity was recorded in passenger air transport services sector.

Marginal Grubel-Lloyd Index
From 254 measures, 104 values were equal to 0, which means that the annual change of international trade in air transport services in these cases had no intra-industry character.On the other hand, 11 measured values were greater than 0,9, which means high intra-industry character of the trade change.
From 190 measures, 94 values were equal to 0, which means that the annual change of international trade in passenger air transport services in these cases had no intra-industry character.On the other hand, 11 measured values were greater than 0,9, which means high intra-industry character of the trade change.
From 183 measures, 94 values were equal to 0, which means that the annual change of international trade in passenger air transport services in these cases had no intra-industry character.On the other hand, 7 measured values were greater than 0,9, which means high intra-industry character of the trade change.

Greenaway-Hine-Milner-Elliot Method
From 289 measures, we recorded the largest turnover of trade in air transport services between the United States and Great Britain in 2002.The smallest turnover value was measured between the United States and Estonia in 2000.Zero value of IIT in air transport services has taken place between the United States and selected countries in two cases with Latvia in 2000 and Lithuania in 2009 and 2010.
From 226 measures, we recorded the largest turnover of trade in passenger air transport services between the United States and Germany in 2007.The smallest turnover value was measured between the United States and Estonia in 2001.Zero value of IIT in passenger air transport services has taken place between the United States and selected countries in 28 cases.
From 222 measures, we recorded the largest turnover of trade in air cargo services between the United States and France in 2001.The smallest turnover value was measured between the United States and Lithuania in 2008.Zero value of IIT in air cargo services has taken place between the United States and selected countries in 34 cases.
As it can be seen from Table 4, it´s not possible to determine a clear trend for development of IIT in air transport services (passenger and air cargo services) for the period from 2000 to 2011.

CONCLUSION
Results of the analysis confirms the existence of IIT in international air transport services (passenger and air cargo services) between the United States and 31 chosen countries between 2000 and 2011.Using traditional and alternative methods, we analysed the intensity, dynamics and turnover of IIT in air transport services (passenger and air cargo services) between the United States and 31 selected countries for the period from 2000 and 2011.Grubel-Lloyd index confirmed the existence of high intensity of intra-industry between the United States and some selected trading partners.Dynamics of trade in air transport services and its components had most of inter-industry nature.The development trend of the IIT in air transport services (passenger and air cargo services) between the United States and chosen trading partners cannot be uniquely determined because of the fluctuating turnover values for each analysed year.We assumed the existence of intra-industry component in the international trade in air transport services and this assumption has been validated through the application of measuring methods.We were able to identify the determinants of intra-industry trade in air transport services by specifying the impact of chosen determinants on international intra-industry trade in air transport services through the econometric analysis.We suggest applying a similar

Table 2
The overview of selected studies on IIT in services

Table 3
Used measurement methods