Which method is NOT included in the financial ratio calculations?

The gross margin ratio is a measure of a company's financial health, but it is not commonly included in traditional financial ratio calculations that focus primarily on the profitability and valuation of a company in relation to its equity or earnings. The other methods listed—debt to equity ratio, net profit margin, and P/E ratio—are standard metrics used to assess a company’s leverage, profitability, and value relative to its earnings, respectively.

The debt to equity ratio evaluates the proportion of equity and debt used to finance a company's assets, providing insights into the financial stability and risk. The net profit margin measures how much profit a company makes for every dollar of revenue, reflecting overall efficiency. The P/E ratio compares a company's current share price to its earnings per share, offering a gauge of how much investors are willing to pay for a dollar of earnings.

While gross margin is indeed a financial metric that indicates how much revenue exceeds direct costs, it is primarily concerned with operational performance and production efficiency rather than broader financial assessment as captured by the other ratios listed. Thus, gross margin ratio stands apart from typical financial ratio calculations associated with overall company valuation or financial leverage considerations.