Abstract
This article investigates the validation of Harberger–Laursen–Metzler hypothesis using Pakistani data over the period of 1978Q1–2012Q4. We have used Gregory–Hansen cointegration approach accommodating structural break in the series. The results confirm the presence of cointegration between the variables. The impact of terms of trade is positive on Pakistan’s trade balance. Domestic income improves local trade balance. Foreign income has a positive impact on Pakistan’s trade balance. The causality analysis indicates the presence of feedback effect between terms of trade and trade balance. Domestic income Granger causes trade balance. The unidirectional causality is running from foreign income to Pakistan’s trade balance. This study opens up new directions for policymakers for improvements in terms of trade to sustain trade balance in Pakistan.
Introduction
Since the advent of industrialization, the economies have opened themselves to rest of the world, global trade emerged and led the small and developing economies to grow faster and developed enormously. The trade liberalization enabled global economies to gain prosperity through trade effect but simultaneously they are facing the major macroeconomic issues of exchange rate and external trade imbalances. In a small open economy, the common policy tool used in response of external trade deficit is to devalue the currency but it causes inflation and high depreciation cost. The changes in terms of trade have a direct effect on trade balance and an indirect effect on savings, income and inflation but unfortunately, this effect varies from country to country. Therefore, researchers have tried to find out the exact relationship between terms of trade and its impact on balance of trade from different economies. The study of Harberger (1950) and Laursen and Metzler (1950) described this phenomenon as terms of trade deterioration will result in a decline in savings due to decrease in real income, and therefore real depreciation will increase real expenditures. This effect is known as the Harberger–Laursen–Metzler (HLM) effect. Recently, the relationship between terms of trade and exchange rate has been the recurrent research topic in the macroeconomic literature. Further, HLM states that the temporary increase in terms of trade may have a positive impact but if shock persists over long run, it would deteriorate the current account and savings. Regrettably, most of the literature on this topic has focused on the short-run analysis and implicitly ignored the long-run effect.
A number of studies on developing countries have examined the relationship between terms of trade and trade balance using different methods, that is, Bahmani-Oskooee (1985) investigated the four developing countries for short-run impact and results support the pattern of movement and satisfied the Marshall–Lerner 1 (ML) condition. Fry (1986) studied the 14 Asian countries to test the HLM effect using three equation model for savings, investment, economic growth and analyzed the terms of trade effect on current account. Grilli and Yang (1988) tested the terms of trade impact over commodity prices rather than on income and concluded that commodity prices effect is different in oil-exporting and non-oil-exporting developing economies. Correia, Neves and Rebelo (1995) checked the same effect on small open economy for terms of trade and real exchange rate. The later studies included Otto (2003), study of Broda (2004) on Malaysian data confirming the long-run relationship, studies by Kaplinsky (2006), Hung-Ju and Hsu (2009), Santos-Paulino (2010), Jawaid and Waheed (2011), Hirose and Ikeda (2012), Idrees and Tufail (2012) and Jääskelä and Smith (2013) and the most recent studies of Bahmani-Oskooee and Xu (2013) and Islam, Shahbaz and Tahir (2013) on the HLM effect on Korea–US and Bangladesh, respectively.
During the last three decades, Pakistan’s economy has also been struggling with the consistent external imbalance shocks and currency devaluation is the sole policy measures taken by the government to offset such shocks. Resultantly, country has been facing double digit inflation and current account has been largely fragile to changes in global and national economic policies. As terms of trade is considered as one of the key operators of change in real income, therefore, it directly impacts national savings and increases dependency on foreign debts. Country’s current account balance has been under stress since decades and expanding on a year-to-year basis. During the last two fiscal years (FY), deficit has increased from US$2.072 billion (FY2012 est.) to US$2.36 billion (FY2013 est.). Again, $1.37 billion is recorded for the first two months of FY2014. Therefore, it is imperative to investigate the effect of increased terms of trade on Pakistan’s trade balance. Following Harberger (1950) and Laursen and Metzler (1950), HLM effect suggests that an exogenous increase in terms of trade in a small but open economy results in an improvement in that country’s trade balance which is appropriate for a developing economy (Berument & Dincer, 2005; Bouakez & Kano, 2008; Chen & Hsu, 2006; Huang & Meng, 2007; Jawaid & Raza, 2013; Sobrino, 2011; Tsen, 2006). Similarly, Pakistan is also one of the developing countries that largely depends on foreign debt liabilities and consecutively facing current account deficit problem. This notion proposes to conduct this study in order to find out the exact relationship between terms of trade and trade balance in Pakistan.
This study tests the HLM effect for Pakistan using autoregressive distributed lag (ARDL) bound testing approach of cointegration and checks both long-run and short-run behaviours of variables in vector error correction model (VECM). However, Granger causality test is also applied in order to explore the exact direction of causality. The results of this study would potentially provide policy guidelines which would lead in achieving steady growth and immutable balance of trade. Subsequently, it may contribute to resist the shocks and stabilize saving and inflation rates in our economy. The remaining article is divided into following sections: the second section presents a brief literature review, model construction and data is given in the third section, the fourth section presents the methodological framework, results and discussion are given in the fifth section and the sixth section presents the conclusion and policy recommendations.
Literature Review
Significant amount of literature is produced which examined the relationship between terms of trade and trade balance but the evidence so far remains inconclusive. However, the scholars generally agree that the impact of change in terms of trade on trade balance may not be similar in every economy. In the theoretical perspective, this notion is known as the HLM effect, based on the seminal works of Harberger (1950) and Laursen and Metzler (1950). The HLM effect predicts that an increase in terms of trade originating from an exogenous shock to a small open economy leads to an improvement in that country’s trade balance. Otto (2003) examined the HLM effect for a number of developing and small Organisation for Economic Co-operation and Development (OECD) economies. 2 The study found that a positive shock to terms of trade improves trade balance but deteriorates later as the shocks become persistent. Dibooglu (2000) pointed out that positive shock to terms of trade is important in the short run but may not sustain in the long run once other factors tend to offset the initial effect. Hoque (1995) found the long-run relationship among current account deficit, terms of trade, domestic income and foreign income using fixed exchange rate regime in the case of Australia. Kouassi, Decaluwe and Colyer (1998) investigated the relationship between terms of trade and current account deficits using the VECM. For Cote d’Ivoire, they find a long-run relationship but point out that current account deficit in Cote d’Ivoire cannot be explained by terms of trade. A strong unidirectional causality runs from current account deficit to terms of trade. The dynamic simulations indicate that a significant portion of fluctuations in terms of trade is explained by current account deficit. The study of Santos-Paulino (2010) provides a similar evidence from small island developing states. Tsen (2009) investigates the impact of terms of trade and oil process on trade balance of Asian economies. The empirical results found that the impact of income terms of trade is different across economies.
A large proportion of available literature exploring the direct relationship between trade balance and terms of trade focus on the correlation between two variables. Only a few have examined the long-run relationship between two series. Haynes and Stone (1982) found a positive relationship between US terms of trade and trade balance. Warner and Kreinin (1983), Gylfason and Risager (1984), Bahmani-Oskooee (1986) and Marquez (1990) found that a deteriorating terms of trade improves trade balance. Bahmani-Oskooee and Jonardhanan (1995) in a 24-country study reported no long-run relationships between two series. Wong (2006) shows that there is a long-run relationship between trade balance and commodity terms of trade but none between income terms of trade and trade balance for Malaysia. Later, these results were validated by Tsen (2006) for Malaysia. Nwachukwu and Egwaikhide (2007) examined the determinant of private saving in Nigeria using HLM hypothesis and found that external terms of trade have a positive impact on private savings. Berument and Dincer (2005) and Zortuk (2008) studied the Turkish economy to examine the long-run impact between terms of trade (income terms of trade and commodity terms of trade) and trade balance. Their study utilized Johansen’s cointegration method, the VECM and Granger causality approaches to test the relationship between income terms of trade and trade balance which showed that there is no causality between the series. Bahmani-Oskooee and Tankui (2008) summarized the relationship between terms of trade and trade balance for 20 African countries. They adopted Pedroni’s (2004) approach using cointegration and confirmed the long-run relationship between both the variables. The results validated the ML requirements where income terms of trade showed a positive impact on trade balance. Another study of Wong (2009) examined the HLM effect for Korea, Hong Kong and Singapore. The empirical results for the long-run relationship between variables indicate that an increase in the terms of trade causes a decline in trade balance. The feedback hypothesis is found between income terms of trade and trade in Hong Kong and Singapore while trade balance Granger causes income terms of trade in Korea. For other Asian countries, Wong (2009) tested the same relationship and found a long-run relationship between the variables but affect of terms of trade on trade balance varies across countries. The empirical evidence showed that domestic demand, foreign income, terms of trade and oil prices are major determinants of trade balance in short run as well as in long run. Besides the work of Wong (2006), very few studies from the above-mentioned literature examined the long-run relationship and most of them used commodity terms of trade 3 which is a form of barter terms of trade. Appleyard and Field (2001) approximate income terms of trade 4 by ratio of exports value to import price. Commodity terms of trade focuses on the relationship between export price and import price, while income terms of trade quantifies the trend of export-based capacity of a country to imports of goods. The high value of commodity terms of trade implies that price of exports is high relative to import prices. However, the direction between commodity terms of trade and income terms of trade may not imply the same thing. An increase in price of exports relative to import could lead to higher commodity terms of trade but income terms of trade could worsen if offset by a decline in quantity of exports. The income terms of trade is a better measure of terms of trade compared to commodity terms of trade because the former can rise faster relative to the latter (see Appleyard & Field, 2001).
Therefore, the present study aims to focus on the income terms of trade for validating that hypothesis in order to draw meaningful insights for Pakistan and provide a certain policy guidelines. Moreover, the methodology and empirical techniques utilized to investigate the relationship between terms of trade and trade balance also play a crucial role in deriving inconclusive and challenging results, hence misleading the policymakers. Therefore, it is imperative to adopt relevant and current techniques which could ensure maximum accuracy in order to derive conclusive evidence which could provide guidelines to policymakers. For example, Idrees and Tufain (2012) test HLM effect using VAR test in a recursive form, and this type of technique only captures the linear interdependence of multiple time series; however, the study of Islam et al. (2013) and Jawaid and Raza (2013) employed ARDL, the VECM Granger test to check HLM effect for Bangladesh and India, respectively. The later study uses the latest technique of estimation and also finds the long-run relationship among the series and hence gives more reliable results for policy design. Therefore, this study uses ARDL model approach of cointegration to empirically examine the small open developing economy of Pakistan. Being a part of a globalized village and to ensure sustainable development goals, it is now imperative to know the relation between terms of trade and balance of trade for Pakistan. The contribution of this article seems significant and the policy implications of this study are highly valuable for both government and international institutions.
The Model Construction and the Data
The aim of the present study is to examine the relationship between income terms of trade and trade balance in Pakistan. The equation of trade balance can be derived by the exports and imports equations, respectively, indicated as follows:
where Xt (Pxt) is real exports (unit price of exports) per capita, Mt (Pmt) is real imports (unit price of imports) per capita, TB t is trade balance which is the difference between exports and imports. The ratio (Pxt/Pmt) between unit value of exports to unit value of imports is termed as terms of trade. Real domestic income per capita is indicated by Yt proxies real gross domestic product (GDP) per capita. Real foreign income (YF t ) per capita is proxied by real GDP of trading partners of Pakistan. If terms of trade is positively linked with trade balance, then we expect ^TT t /^TB t > 0 otherwise ^TT t /^TB t < 0. The rise in domestic income has a burden on import bill due to hike in imports demand and we expect ^Yt/^TB t < 0, otherwise ^Yt/^TB t < 0. If an increase in foreign income will increase the demand for Pakistan’s exports, then foreign income has a positive impact on trade balance and we expect ^YF t /^TB t > 0, otherwise ^YF t /^TB t < 0. We have converted all the series into logarithm for results reliability and efficiency. The study covers the period of 1978Q1–2012Q4. We have collected data for real effective exchange rate, unit value of export and unit value of imports from International Financial Statistics (CD-ROM, 2013). The real GDP per capita of Pakistan and her trading partners is collected World Development Indicators (CD-ROM, 2013). 5
Methodological Framework
This study employs ARDL bounds testing approach to cointegration proposed by Pesaran, Shin and Smith (2001) to check the long-run relationship among terms of trade, domestic income, foreign income and trade balance in the case of Pakistan over the period of 1978Q1–2012Q4. The ARDL cointegration framework using bound testing approach is a more suitable approach because it analyzes the relationship between dependent variable and regressors even when it is uncertain whether the regressors under observation are trend or stationary. In this process, two separate critical values are associated with all regressors that generate critical value bounds and classified as purely I(1) or purely I(0) or mutually I(1)/I(0) cointegrated. Following this process, a conclusion can be drawn on the basis of F-statistics 6 without knowing the order of integration of variables and this method is also suitable for small sample analysis, that is, Pakistan. Assuming the possibility of structural break in the underlying series, in addition to the ARDL approach to cointegration, we also utilized Gregory–Hansen structural break cointegration test developed by Gregory and Hansen (1996). This test has a uniqueness to point out the structural break in the series and these dates are endogenously determined without affecting the rest of the series. Moreover, a dynamic unrestricted error correction model (UECM) is also generated from the ARDL bounds testing through a simple linear transformation. The UECM combines the short-run dynamics with the long-run equilibrium without losing any long-run information. The UECM is expressed as follows:
In the above equations, the firstt-difference operators are denoted by Δ and μt represents residual terms. Keeping in view of the sensitivity of F-statistic with lag order selection, the suitable lag length of the first-differenced regression is selected on the basis of the minimum value of akaike information criterion (AIC) since the inappropriate lag length selection may lead to misleading results. Pesaran et al. (2001) suggested an F-test to evaluate the joint significance of the coefficients of lagged level variables. For example, the null hypothesis for cointegration between the variables is H0: αTT = αTB = αY = αYF = 0, while the rejection of null hypothesis for cointegration is Ha: αTT ≠ αTB ≠ αY ≠ αYF ≠ 0. Pesaran et al. (2001) generated two asymptotic critical values, that is, upper critical bound (UCB) and lower critical bound (LCB), that are used to determine the existence of cointegration between the series without knowing the order of integration. The LCB is used to test cointegration if all the series are integrated at I(0); otherwise, we use UCB. Our computed F-statistics are FTB(TB/TT, Y, YF), FTT(TT/TB, Y, YF), FY(Y/TB, TT, YF) and FYF(YF/Y, TB, TT) for equations (7)–(10), respectively. In the ARDL bound testing approach, the existence of a long-run relationship between the variables is calculated in the basis of F-statistic. If the F-statistic falls outside the UCB, then there is cointegration between the series or if our calculated F-statistic falls within LCB, then there is no cointegration. Similarly, the decision regarding cointegration is inconclusive if calculated F-statistic falls between LCB and UCB. In such scenario, an error correction method is adopted which is an easy and suitable way to examine cointegration between the variables. Here, we have used critical bounds generated by Narayan (2005) to test cointegration rather than those generated by Pesaran et al. (2001) and Turner (2006).
The VECM Granger Causality
After determining the long-run relationship among the variables, we use the Granger causality test to assess the causality between the variables. In case the cointegration exists between the series, the VECM can be developed as follows:
It is mentioned in the VECM model that the difference operator is represented by (1 – L) and ECMt–1 denotes the lagged error correction term, generated from the long-run association. The statistical significance of estimate of the lagged error term, that is, the negative sign of ECTt–1 confirms the existence of the long-run causal relation using the t-statistic. However, the short-run causality is identified by the joint χ2 statistical significance of the estimates of first-difference lagged independent variables. For example, the significance of α22,i ≠ 06 i suggests that the terms of trade Granger causes trade balance and causality runs from trade balance to terms of trade can be indicated by the significance of β22,i ≠ 06 i . The same inference can be drawn for rest of causality hypotheses. Finally, we use Wald or F-test to test the joint significance of estimates of lagged terms of independent variables and error correction term.
Results and Discussions
The descriptive statistics and correlation matrix are reported in Table 1. The results showed that all the series are normally distributed which is indicated by the statistics of Jarque–Bera normality test. This implies that series have zero mean with constant variance. The correlation analysis reported indicates that terms of trade and domestic income are positively correlated with trade balance. A negative correlation is also found between foreign income and trade balance. There exists a positive correlation from domestic and foreign incomes to terms of trade. Finally, foreign income is positively correlated with domestic income.
Descriptive Statistics and Correlation Matrix
The long-run relationship among the variables has been examined using the ARDL cointegration framework with bound testing approach. However, the condition for utilizing this approach is that if the variables are integrated either at I(0) or I(1) or I(0)/I(1). Therefore, to ensure this condition that none of the variables is stationary at I(2) or beyond this level, we have applied augmented Dickey–Fuller (ADF) unit root test by Dickey and Fuller (1979), Dickey and Fuller generalized least-squares (DF-GLS) unit root test by Elliot, Rothenberg and Stock (1996) and Ng–Perron unit root test by Ng and Perron (2001). These unit root tests determine that all the variables have unit root problem at their level form but were found to be integrated at I(1). 7 However, Baum (2004) pointed out that unit root analysis by ADF, DF-GLS and Phillips–Perron (P–P) unit root tests may provide biased results due to structural break that might occur in the series.
In order to resolve this issue, we have also obtained two structural break unit root tests such as Zivot and Andrews (1992) unit root test which provides information about one structural break and Clemente–Montanes–Reyes (1998) de-trended structural break unit root test that contains information about two structural breakpoints in the series. Moreover, Clemente–Montanes–Reyes unit root test administers information about two possible structural breakpoints in the series through (i) an additive outliers (AO) model that seeks out an abrupt change in the mean of the series and (ii) an innovational outliers (IO) model that directs gradual shifts in the mean of the series. As a result, the AO model is more consistent for series having sudden structural changes when compared with gradual shifts.
The results reported in Table 2 show that trade balance, terms of trade, domestic income and foreign income are found to be non-stationary at their level. The variables are stationary at first-differenced form. This implies that the series are integrated at I(1). The unique level of integration of the variables leads us to apply the ARDL bounds testing approach to test cointegration among trade balance, terms of trade, domestic income and foreign income in the case of Pakistan over the period of 1978Q1–2012Q4. After confirming that all the series are integrated at I(1), the model is now ready for the analysis of cointegration relationship between the series using the ARDL bounds testing approach. The selection of an appropriate lag length of the variables using AIC and Schwarz’s Bayesian criterion criteria is a necessary step before the ARDL bounds test is applied (Tiwari & Shahbaz, 2013). It is described by Lütkepohl (2006) that AIC lag length criteria provide efficient and consistent results to capture dynamic relation between the variables. Therefore, using the AIC criteria, the optimal lag length of the variables is mentioned in the second column of Table 3 along with the results of the cointegration test. In order to determine whether cointegration between the variables exists or not, we have to compare our calculated F-statistic by following null hypothesis, that is, no cointegration with critical bounds such as LCB and UCB. The results reveal that there are two cointegrating vectors. This represents the cointegration relationship at 1 and 5 per cent significance levels when terms of trade and trade balance are treated as response variables. The results reported in Table 3 show that a long-run relationship among trade balance, terms of trade, domestic income and foreign income exists in the case of Pakistan.
Zivot–Andrews Structural Break Trended Unit Root Test
The Results of ARDL Cointegration Test
It is also noticed that the presence of structural break in the time series makes long-run relations biased, weak and unreliable. To avoid this issue, we have applied Gregory–Hansen (1996) structural break cointegration test that does not only remove this deficiency of the ARDL bounds testing approach to cointegration but also ensure the robustness of long-run relationship among trade balance, terms of trade, domestic income and foreign income. The Gregory–Hansen cointegration test is powerful over residual-based cointegration tests and adjusts the presence of one structural break in the series. The results are reported in Table 4. The results show that cointegration relationship exists among trade balance, terms of trade, domestic income and foreign income after allowing structural breaks in 1981 and 2003 which was investigated by applying fully modified ordinary least-square (FMOLS) approach. This approach indicated the statistical significance of the dummy variable for structural break in trade sectors of Pakistan. The structural breaks in trade reforms include competitiveness, concentration of exports and openness for agricultural in 1980s and implementation of national export policy in 2002. The empirical evidence indicated that there is a cointegration relationship between the variables as trade balance and terms of trade are used as forcing variables including dummy variable. This implies that a long-run relationship exists between the variables and long-run results are robust.
Gregory–Hansen Structural Break Cointegration Test
Table 5 reports the results of long- and short-run analyses. The results reveal that commodity terms of trade have a positive impact on trade balance in Pakistan. All else same, a 1 per cent increase in terms of trade leads trade balance by 0.2795 per cent. 8 It is statically significant at 1 per cent level of significance. This validates the HLM effect which reveals that an increase in terms of trade improves trade balance in the case of Pakistan. These findings are consistent with Wong (2006) for Malaysia, Zortuk (2008) for Turkey but contradictory with Wong (2009) for Hong Kong. The positive impact of domestic income on trade balance shows the presence of absorption theory. Theory of absorption discloses that an increase in domestic income raises the demand for money and that would subsequently increase exports that will improve in trade balance. Keeping other things constant, a 1 per cent increase in per capita income adds in trade balance by 0.1229 per cent. Shahbaz, Awan and Ahmad (2011) also indicated a positive effect of income on trade balance but it is statistically insignificant. This may be due to the use of different proxies for terms of trade and data span as well as data frequency. 9 A positive and statistically significant relationship is found from foreign income to trade balance in the case of Pakistan. This shows that an increase in income of world will raise demand for Pakistani products which in result improves trade balance of the country. A 1 per cent increase in world income is linked with 0.1094 per cent improvement in trade balance, all else same. This finding is same as that of Shahbaz et al. (2011) but coefficients are different due to differences in data frequencies and time spans.
Long- and Short-run Results
The short-run results are shown in Table 5. Our results indicate that terms of trade improve trade balance and it is statistically significant at 1 per cent level. The impact of national income (foreign income) has a positive (negative) impact on trade balance but insignificant. The results show the significance of lagged error term, that is, ECMt–1 while estimate has a negative sign. The statiscally significant lagged error terms verify our established cointegration relationship among terms of trade, domestic income, foreign income and trade balance in the case of Pakistan. The coefficient of ECMt–1 is –0.4575 and it is significant at 1 per cent level. We note that changes in terms of trade are modified by 45.75 per cent in each quarter. This implies that convergence would take more than 2 years to range the stable path of equilibrium which is an indication of very fast and significant adjustment process for Pakistan in any shock to trade balance equation.
The model is also tested for sensitivity analysis by using stability test of cumulative sum of recursive residuals (CUSUM) and the CUSUM of square (CUSUMSQ) suggested by Brown, Durbin and Evans (1975). Hansen argued that misspecification of model may provide biased results that further lead to misinterpretation of results. The CUSUM and CUSUMsq tests are applied as diagnostic tests in order to ensure the adherence of parameters. Further, Brown et al. (1975) suggested that these tests provide help in analyzing the possible changes in parameters. The expected value of recursive residual is zero which leads us to accept that null hypothesis of parameter constancy is correct, otherwise not.
The plots of both CUSUM and CUSUMsq are shown in Figures 1 and 2 at 5 per cent level of significance. The results indicate that plots of both tests are within critical bounds at 5 per cent level of significance. Table 5 shows the results of diagnostic tests. The results signify that the short-run model successfully passes all the tests of normality, serial correlation, autoregressive conditional hetero-skedasticity, white heteroskedasticity and functioning form of the model. It is also evident that normality of residual term is proved by Jarque–Bera estimates, and no serial correlation is observed during short span of time. Similarly, no evidence of autoregressive conditional heteroskedasticity is found and same inference can be seen for white heteroskedasticity. The functional form of the short-run model is well justified and is confirmed by the estimates of Ramsey regression equation specification error (RESET) test. The stability and sensitivity analysis show that the ARDL and short-run results are stable and reliable for policy purpose regarding trade balance in the case of Pakistan.


The long-run and short-run analyses just show the impact of independent variables on dependent variables and ignore the cause and effect of the variables (direction of causal relationship between the variables). This is solved by applying the VECM Granger causality approach. Table 6 reports the empirical findings of the VECM Granger causality framework. In the long run, we find that the feedback effect exists between trade balance and terms of trade. Domestic and foreign incomes Granger cause trade balance. Terms of trade is Granger caused by domestic and foreign incomes. In shortrun causality analysis, trade balance Granger causes terms of trade and in result, terms of trade Granger cause trade balance. The unidirectional causality is found to be running from foreign income to trade balance. Foreign income is Granger caused by terms of trade and trade balance in Pakistan.
In an economic literature, it is argued that the Granger causality approaches, such as VECM Granger causality test, possess some limitations, that is, the causality test does not acquire the relative strength of causal relation between the variable beyond the specified time limit. This weakens the reliability of causality results by the VECM Granger approach. However, the innovative accounting approach (IAA) provides solution to this problem. The IAA is a combination of variance decomposition method (VDM) and impulse response function (IRF). The variance decomposition approach determines the response of the dependent actor to shocks stemming from independent actors. Therefore, we applied the IRF and VDM. The IRF is an alternative to VDM. Table 7 shows the results of VDM, while the IRF graph is shown in Figure 3. The variance decomposition approach indicates the magnitude of the predicted error variance for a series accounted for by innovations from each of the independent variable over different time horizons beyond the selected time period.
The VECM Granger Causality Analysis
Variance Decomposition Method
Table 7 reports the empirical evidence regarding VDM and results reveal that innovative shocks of terms of trade, domestic income and foreign income contribute to trade balance by 35.97, 1.76 and 9.79 per cent and rest is explained by innovative shock of trade balance itself. Trade balance is explained by 52.46 per cent of its own shocks. The response of terms of trade due to shocks in trade balance is 28.30 per cent. The contribution of domestic income and foreign income to explain trade balance is 10.24 and 6.62 per cent, respectively.
Trade balance contributes to economic growth by 22.39 per cent. Domestic income is 68.31 per cent contributed by terms of trade. Foreign income contributes to domestic income by 2.90 per cent. Trade balance, terms of trade and domestic income contribute to foreign income by 14.05, 21.44 and 1.59 per cent, respectively. Overall results show that the feedback effect exists between trade balance and terms of trade. Trade balance and terms of trade cause domestic income. Foreign income is caused by terms of trade.
The IMF traces the time path of the impacts of shocks of independent variables on the dependent variables in a VAR system. The IMF is an alternative to VDM showing how long independent variable reacts to shock stemming in the dependent variables. We can see the magnitude of the response of trade balance to its own shock, those of terms of trade, domestic income and foreign income. Trade balance responds positively due to forecast error stemming in terms of trade. The response in domestic income is inverted U-shaped and foreign income responds positively after third time horizon due to forecast error stemming in terms of trade. The response in terms of trade, domestic income and foreign income is fluctuating due to forecast error stemming in trade balance. The contribution of domestic income to trade balance, terms of trade and foreign income is positive. Trade balance and terms of trade respond positively but response of foreign income in domestic income is minimal and fluctuating.
Concluding Remarks and Policy Recommendations
This article explored the validation of HLM effect by incorporating domestic income and foreign income in trade balance function in case of Pakistan. We have employed the ARDL bounds testing to investigate the long-run relationship between the variables. We find that trade balance, terms of trade, domestic income and foreign income are cointegrated for long-run relationship. Moreover, improvement in terms of trade improves trade balance which validates the HLM effect in Pakistan. Domestic income improves trade balance. Foreign income is positively linked with trade balance. The causality analysis by IAA reveals that terms of trade causes trade balance and trade balance leads terms of trade. Domestic income is cause of trade balance, whereas terms of trade causes foreign income.

The results of this study suggest that Pakistan has the capability to benefit from the improved terms of trade if foreign investment is attracted. However, in the past, the conventional way of dealing with deteriorating terms of trade has been the currency devaluation that has not been successful and balance of trade remained fragile to external shocks due to weak price elasticity of demand for Pakistani exports. This orthodox policy must be replaced by paying attention towards the new policy to increase foreign investment. It does not only improves balance of payment and growth but also improves terms of trade as a rebound in the long run. Due to increase in the foreign investment, the exports flourish both in terms of volume and composition. The analysis also suggests that if the investment is diverted more towards the production of such goods and services that cover larger part of country’s imports, it would guarantee higher outcomes of improved terms of trade.
We are aware about the limitations of our study. For instance, this article indicates the partial impact of income terms of trade on trade balance in Pakistan. To capture the complete impact of terms of trade on trade balance, commodity terms of trade should also be considered for empirical analysis (we have used income terms of trade). Few studies have investigated the impact of currency devaluation on trade balance (Shahbaz, Awan & Ahmad, 2011, Shahbaz, Jalil & Islam, 2012a) and domestic output (Shahbaz, Islam & Aamir, 2012b). The Marshal Learner Condition was also empirically investigated (Aftab & Aurangzeb, 2002; Aftab & Khan, 2008). Such studies could not provide any help to policymakers in designing a comprehensive trade policy for the removal of trade deficit. This shows the importance of further comprehensive research investigating the impact of currency devaluation and terms of trade (income terms of trade and commodity terms of trade) on trade balance, exports, imports and domestic output using time-varying cointegration, time-varying Granger causality and time-varying long-run estimates. The time-varying cointegration, causality and long-run estimates provide efficient empirical evidence due to their high explanatory powers.
Footnotes
Acknowledgements
The authors/author is/are grateful to the anonymous referees of the journal for their extremely useful suggestions to improve the quality of the article. Usual disclaimers apply.
