Exhibit AlReturn on Assets for Merck and Merck’s 10 Largest Competitors, 1970-198421.0% -20.0% -19.0% -18.0%Return on Assets17.0%-16.0% -15.0% -14.0% -13.0% -12.0% -11.0% -10.0% -19701971 -1972 -19731974 -1975 -1976 -1977 -1978 -19791980 -1981 -19821983 -1984YearNote: Return on assets, defined as after-tax income plus interest divided by assets, obtained from Compustat. The list of Merck’s 10largest competitors (as measured by sales, SIC code 2834) has generally varied from year to year, due to takeovers, acquisitions,and different rates of growth. The companies depicted in the graph (and the years during which they were one of Merck’s 10largest competitors) are Abbott Laboratories (70-73, 75-84), American Home Products (70-84), Baxter International (85-84),Bristol-Myers (70-84), International Minerals & Chemicals (70, 71, 74-81), Johnson & Johnson (70-84), Eli Lilly & Co (70-84),Pfizer Inc (70-84), Schering-Plough (82), Smithkline Beckman Corp (80-84), Squibb (70-78, 84), Sterling Drugs (70-79, 83),Upjohn (72-74, 78-84), and Warner-Lambert (70-84).