TABLE 2.

Estimation of link function (Park tests) and family distribution (Box–Cox tests) of unit price of pharmaceutical products.

Study sample	Modified park test for family distribution		Box-cox test for link function
Total	1.77	Gamma	−0.13	Log
Subsample by ownership
Domestic suppliers outside of top 100	1.98	Gamma	−0.07	Log
Top 100 domestic suppliers	2.02	Gamma	−0.20	Log
Suppliers with joint venture	2.09	Gamma	−0.24	Log
Foreign-owned suppliers	3.53	Inverse gaussian	−0.33	Log
Subsample by medicines
Original brand	3.53	Inverse gaussian	−0.25	Log
Generic	1.84	Gamma	−0.10	Log
Subsample by administration routes
Injectable	2.00	Gamma	0.03	Log
Oral	1.72	Gamma	0.42	Square root

Note: Coefficients excerpted from modified Park tests: 0 = Gaussian distribution (variance unrelated to the mean); 1 = Poisson distribution (variance equal to the mean); 2 = Gamma distribution (variance exceeding the mean); 3 = Inverse Gaussian distribution (or Wald distribution). Coefficients excerpted from Box–Cox tests: 0 = log link; 0.5 = square root link; 1 = identity link.