Boston Celtics win percentages per decade: The number of seasons
with win % in the following ranges:
                                                    Decade
          Yrs.    80%+ 60-79% 40-59% 20-39% 0-19%    Ave.    Wins Losses
 2000s:     9      1      0      7      1      0     49.9     368   370
 1990s:    10      0      3      4      2      1     47.8     377   411
 1980s:    10      1      8      1      0      0     72.2     592   228
 1970s:    10      1      4      3      2      0     58.2     477   343
 1960s:    10      0      9      1      0      0     71.5     571   228
 1950s:    10      0      4      5      1      0     57.8     408   298
 1940s:     3      0      0      2      1      0     39.9      67   101
Totals:    62      3     28     23      7      1     59.1    2860  1979

Per decade, the number of appearances in 
each playoff round:
                                    Yrs in    Yrs in   Yrs in
                  Finals   Yrs in   Conf.     Conf.    Round    Yrs in
          Yrs.     Wins    Finals   Finals    Semis    of 16   Playoffs
 2000s:     9        1        1        2        3        5        5
 1990s:    10        0        0        0        2        5        5
 1980s:    10        3        5        8        9        7       10
 1970s:    10        2        2        5        6        1        6
 1960s:    10        9        9       10        4        0       10
 1950s:    10        2        3        6        5        1       10
 1940s:     3        0        0        0        1        0        1
Totals:    62       17       20       31       30       19       47