broad-scale investment decisions investors may want to know how various types of investments have per- formed during booms, recessions, high inflation and low inflation. The table shows how 10 asset categories per- formed during representative years since World War II. But history rarely repeats itself, so historical performance is only a rough guide to the figure.     Average Annual Return on Investment*   Investment Recession Boom High Inflation Low Inflation   Bonds (long-term government) 17% 4% 1% 8% Commodity index 1 6 15 5 Diamonds (1-carat investment grade) 4 8 79 15 Gold (bullion) 8 9 105 19 Private home 4 6 6 5 Real estate (commercial) 9 13 18 6 Silver (bullion) 3 6 94 4 Stocks (blue chip) 14 7 3 21 Stocks (small growth-company) 17 14 7 12 Treasury bills (3-month) 6 5 7 3   *In most cases, figures are computed as follows: Recession-average of performance during calendar years 1946, 1975, and 1982; boom- average of 1951, 1965, and 1984; high inflation-average of 1947, 1974, and 1980; low inflation-average of 1955, 1961, and 1986. Gold figures are based only on data since 1971 and may be less reliable than others. Commercial real estate figures are based only on data since 1978 and may be less reliable than others. Sources: Commerce Dept.; Commodity Research Bureau; DeBeers Inc.; Diamond Registry; Dow Jones & Co.; Dun & Bradstreet; Handy & Harman; Ibbotson Associates; Charles Kroll (Diversified Investors Forecast); Merrill Lynch; National Council of Real Estate Investment Fiduciaries; Frank B. Russell Co.; Shearson Lehman Bros.; T. Rowe Price New Horizons Fund.