Care must be taken to select a consistent time frame for the price and earnings components.
Price usually refers to today's closing stock price.
The Nasdaq-100 index is comprised of individual stocks which have different market capitalizations. The reason for this is that the Nasdaq-100 is comprised of 100 independent companies, not 100 departments of one company. Adding CSCO's earnings to CMGI's losses to arrive at a NET earnings number is unreasonable, especially when companies like CMGI drag down Nasdaq-100's earnings so dramatically. This argument suggests we count these negative earnings numbers as 0 instead of subtracting the actual negative earnings AND we remove those losing companies' market capitalization from the summed market cap list, too. In other words, assume the worst case, which is that a losing company goes bankrupt, it disappears, it no longer has losses, and its stock become worthless.