By LINDA A. JOHNSON Pfizer Inc., the world's biggest drug company, is laying off up to 800 scientists this year in its latest effort to refocus disappointing research efforts and cut its massive overhead ahead of an anticipated crash in revenue.New York-based Pfizer plans to reduce its global research staff - currently about 10,000 people - by 5 percent to 8 percent this year, company spokeswoman Kristen Neese said Tuesday."This is in line with our refocused research areas," Neese said.The move comes after the company announced in September that it was narrowing its research focus to six disease areas - Alzheimer's, cancer, schizophrenia, pain, inflammation and diabetes - and abandoning new research in other areas.That included cardiovascular disease, where Pfizer had been a dominant player with its $13 billion-a-year cholesterol fighter Lipitor, the world's top-selling drug.