My minimum wage worksheet

My minimum wage worksheet -- the easily could-have-been minimum wage double-indexed for inflation and per capita income growth:
 
yr  per capita    real    nominal  dbl-index  %-of

68    15,473    10.69      (1.60)                 100%
69-70-71-72-73          [real, low point -- 8.39]
74    18,284      9.43      (2.00)     12.61          
75    18,313      9.08      (2.10)     12.61
76    18,945      9.40      (2.30)     13.04     72%
77                                                             [8.84]
78    20,422      9.45      (2.65)      14.11
79    20,696      9.29      (2.90)      14.32
80    20,236      8.75      (3.10)      14.00         
81    20,112      8.57      (3.35)      13.89     62%
82-83-84-85-86-87-88-89                        [6.29]
90    24,000      6.76      (3.80)      16.56
91    23,540      7.26      (4.25)      16.24     44%
92-93-94-95                                              [6.50]
96    25,887      7.04      (4.75)      17.85
97    26,884      7.46      (5.15)      19.02      39%
98-99-00-01-02-03-04-05-06                    [5.95]
07    29,075      6.56      (5.85)       20.09
08    28,166      7.07      (6.55)       19.45
09    27,819      7.86      (7.25)       19.42      40%
10-11-12                                                     [7.36]                 
13   29,209?     7.25      (7.25)        20.20?    36%?

 * * * * * * 
An added thought: By the year 2013 some could speculate that a $20.20/hr minimum wage might not be a realistic expectation evidenced by double indexing alone because the fabric of the economy might have changed so radically over 45 years.  Might be an outside possibility, but, LBJ's 1968 minimum wage would have morphed to more than $14/hr with double indexing by only 1978.  Can anyone explain how the economic fabric might have changed sos radically in a mere 10 years?