Your friend has started a medical billing outsourcing business. His clients are mainly doctors. After the patient gets treated, the doctor's office sends your friend's company the paperwork for each patient (e.g., the reason for the visit, diagnostic tests done, referrals made, complexity of the visit, nature of treatment given, details of patient's insurance, etc.). Your friend's company then files the insurance claim with the respective insurance companies, sends them the details of the claim, follows up with them for payments and clarifications, collects payments, and then makes the payment to the doctor. Thus, the main clientele are independent doctors who have outsourced the insurance work to your friend's company. Hospitals and patients are not your friend's customers. Your friend is interested in knowing the number of employees he needs to hire in the next three to four years (long-range HR planning). He has asked you for your assistance in identifying the appropriate method for forecasting HR supply and demand for his business. Discuss the methods you would suggest and the justification for the methods or methods.