What is the basis of these screening ratios?

Since the share market is a recent phenomena, the parables of which were not available during the times of Prophet Mohamad ﷺ, there is nothing specific related to these in the Quran and Sunnah. Therefore, scholars on the basis of  qiyaas (analogy) , ijma (consensus) have  proposed these ratios in order to enable Muslims to participate and benefit from the economic development.