When the coefficient constraints=,=, the equation requires domestic and foreign price indexes are symmetry. It also requires domestic and foreign relative prices are proportional to the exchange rates. So it is still a strict form of PPP and can be regarded as the test of absolute PPP. If the values of the coefficient and are not equal to and then they can be seen as the test of relative PPP. When the values are equal but have opposite signs, then domestic and foreign price indices is dynamic symmetry. Although researchers recognize that the PPP may only be valid in the long term, they have not used the concept of dynamic to distinguish short-term and long-term effects of PPP yet. The results often refuse the PPP hypothesis when testing this model. Therefore some economists explain that, the reason why PPP is rejected can be subject to temporary shocks of economy or price stickiness in commodity markets, in the long run, it should be able to fully foresee the convergence of exchange rate to PPP.
当约束系数=，=，方程需要国内和国外的价格指标的对称性。这也需要国内和国外的相对价格的汇率比例。所以它仍然是一个严格的PPP可以看作是绝对购买力平价检验。如果系数的值不等于就可以看作是相对购买力平价检验。当值相等，但符号相反，那么国内和国外的价格指数是动态的对称性。尽管研究人员认识到PPP只能在长期内是有效的，他们没有使用动态的概念来区分短期和长期影响PPP呢。结果常常拒绝PPP假设测试时，该模型。因此一些经济学家解释说，之所以购买力平价是拒绝可能受到冲击的经济或商品市场价格粘性，从长远来看，它应该能够充分预见汇率PPP收敛。