There are several methodologies that you can consider for your research paper on the effectiveness and limitations of the discounted cash flow (DCF) approach of corporate valuation in the healthcare sector. Here are a few options:

1. Literature Review: Conduct a comprehensive review of existing literature on the DCF approach and its application in the healthcare sector. Analyze the findings from various studies and identify the common themes, strengths, and weaknesses of using DCF in valuing healthcare companies.

2. Case Study Analysis: Select a few healthcare companies and analyze their valuation using the DCF approach. Compare the results with other valuation methods, such as market multiples or comparable transactions. Discuss the effectiveness and limitations of DCF in capturing the unique characteristics of the healthcare sector.

3. Survey or Interviews: Design a survey or conduct interviews with professionals working in the healthcare industry, such as financial analysts, investment bankers, or healthcare executives. Gather their opinions and insights on the effectiveness and limitations of the DCF approach in valuing healthcare companies. Analyze the responses and draw conclusions based on the collected data.

4. Quantitative Analysis: Collect financial data of healthcare companies and perform a quantitative analysis to evaluate the accuracy and reliability of the DCF approach in predicting future cash flows and valuations. Compare the DCF-based valuations with actual market prices or transaction values to assess the effectiveness of the approach.

5. Comparative Analysis: Compare the DCF approach with other valuation methods commonly used in the healthcare sector, such as the cost of capitalization or the net asset value method. Analyze the strengths and weaknesses of each method and discuss their suitability for valuing healthcare companies.

6. Simulation or Sensitivity Analysis: Use simulation techniques or conduct sensitivity analysis to assess the impact of key assumptions and variables on the DCF-based valuations of healthcare companies. Evaluate the robustness of the DCF approach and identify its limitations in capturing uncertainties and risks specific to the healthcare sector.

Remember to choose a methodology that aligns with your research objectives, available resources, and the nature of data you can access. Additionally, consider consulting with your research advisor or supervisor for further guidance on selecting the most appropriate methodology for your study.