What method involves studying a firm's past employment needs to predict future needs?

The correct method for studying a firm's past employment needs to predict future needs is forecasting. This involves analyzing historical data—like past hires, turnover rates, and industry trends—to project what the organization's staffing requirements will be in the future. Forecasting is crucial for human resource planning, as it allows HR professionals to align the workforce with the organization’s goals and adapt to changes in the business environment.

Trend analysis, while related, focuses specifically on identifying patterns over time rather than making direct predictions. Workforce analytics is a broader field that encompasses various methods, including forecasting, to derive insights from workforce data but does not focus solely on predicting future needs based on past employment patterns. Computer analysis is a general term that describes the use of technology to process data but does not specifically refer to the method of predicting employment needs.

Thus, forecasting is the most aligned method for projecting future workforce needs based on historical employment data, making it the correct choice.