Group

Length of time

Max

Min

Average

Standard deviation

1

6 months

1.9728

0.1866

1.1305

0.0794

2

12 months

2.1555

0.5288

1.1916

0.0649

3

18 months

2.3744

0.6496

1.2257

0.0627

4

24 months

2.0877

0.6181

1.1930

0.0546

5

36 months

2.0069

0.5443

1.1634

0.0508

6

48 months

1.9497

0.5461

1.1762

0.0464

7

60 months

1.9127

0.5460

1.1716

0.0435

8

72 months

1.8801

0.5059

1.1647

0.0416