i am studying the impact of trade openness on manufacturing growth from 1967 to 2013 in Tunisia. My variables are Manufacturing value added(MVA), openness(OPEN), GFCF and manufacturing labor force (MLAB) 1/ MVA (lag1) and MLAB (lag4) are I (0) no constant , no trend MVA, OPEN and GFCF are stationary at first difference and satisfy the 3 equations of ADF test, but MLAB at first difference is only stationary when I include constant and trend. can I claim that MLAB is stationary at first difference (I mean is not I (2))?
Can I run ARDL model in this case?
2/I include trend and intercept in my ARDL model but their coefficients are not significant, what should I do?
Can I delete them and estimate again my model? In this case what critical value I should consider for my ARDL model? Unrestricted intercept and unrestricted trend //or no intercept and no trend because their coefficient are not significant. What is best software I can use?