*5.2. Stationarity Tests*

The values of all economic variables were transformed into logarithmic values and tested for the stationarity of the series. The test results of the Augmented Dickey-Fuller (ADF) and Phillips Perron (PP) tests presented in Table 2 show that there was no stationarity in the level data for export, real exchange, Real GDP, price, and foreign direct investment. The absolute value of their test statistics was less than the absolute value of 5 percent critical value of −2.927. However, the first differences of the series (Table 3) were stationary, implying that they were all integrated of degree 1 (I (1)). Foreign GDP and real interest rate were stationary at the level data (I (0)). This indicated that the series were integrated of different levels, such that the Auto Regressive Distributed Lagged (ARDL) bounds test approach proposed by Reference [32] is an appropriate method for analyzing the long-run relationship between the series. Consequently, the ARDL bound test approach was used for this study.


**Table 2.** Unit root tests at the levels of the variables.

Note: \*\* are significance at 0.05 significance level for the critical value of −2.960411.

**Table 3.** Unit root tests at the first differences of the variables.


Note: \*\*\* and \*\* are significance level at 1% and 5% respectively. Critical value at 0.05 level, −2.967767.
