Periodical Group

Average AC

SD

Significance Level (p)

A = 1959-1969

177

28

A < C (0.0021); C < D (0.0066)

B = 1970-1979

168

25

A < D (<0.0001); C > E (<0.0001)

C = 1980-1989

285

76

B < C (0.0014)

D = 1990-1999

383

112

B < D (<0.0001)

E = 2000-2010

126

104

D > E (<0.0001)