Table 2 Comparison of time series data among the OD (off-duty), 2NS (two night shifts) and 4NS (four night shifts) groups

Wisconsin Card Sorting Test

Number of categories

Off-duty

7.6 ± 1.9

8.0 ± 1.5

8.5 ± 1.3

8.8 ± 1.2

0.08

0.926

Two night shifts

7.9 ± 2.3

8.4 ± 2.2

8.2 ± 2.3

8.1 ± 2.2

Four night shifts

8.4 ± 1.4

8.3 ± 1.2

8.3 ± 1.3

8.3 ± 1.1

% of conceptual level responses

Off-duty

73.7 ± 14.5

79.4 ± 8.9

81.7 ± 8.2

84.7 ± 5.9

0.81

0.449

Two night shifts

76.7 ± 15.7

79.4 ± 13.1

78.8 ± 15.0

77.6 ± 14.8

Four night shifts

81.2 ± 7.1

82.0 ± 6.7

81.6 ± 6.0

83.8 ± 3.1

Failure to maintain set

Off-duty

1.2 ± 0.9

1.8 ± 1.4

1.4 ± 1.3

1.4 ± 1.4

2.47

0.094

Two night shifts

1.2 ± 0.8

1.6 ± 1.2

1.2 ± 1.1

1.3 ± 1.6

Four night shifts

1.8 ± 1.3

1.8 ± 1.3

1.7 ± 1.3

2.3 ± 1.3

Digit Symbol Substitution Test

Scoring scale

Off-duty

14.7 ± 1.6

15.2 ± 1.9

15.6 ± 1.9

16.5 ± 2.1

4.72

0.013^a

Two night shifts

13.3 ± 2.8

14.0 ± 2.7

14.4 ± 2.8

14.4 ± 2.9

Four night shifts

12.1 ± 3.5

13.4 ± 2.9

14.0 ± 2.8

14.2 ± 2.0

Symbol Searching Test

Scoring scale

Off-duty

14.4 ± 1.1

15.5 ± 2.6

15.6 ± 2.0

16.7 ± 1.8

6.28

0.003^a

Two night shifts

13.3 ± 3.2

13.8 ± 2.4

14.4 ± 3.1

14.9 ± 2.8

Four night shifts

11.7 ± 4.1

12.8 ± 3.6

12.7 ± 3.5

14.1 ± 2.8

Information process index

Off-duty

126.0 ± 7.7

130.3 ± 10.7

131.5 ± 9.2

137.7 ± 9.0

7.21

0.002^a

Two night shifts

118.0 ± 14.6

121.6 ± 13.2

124.6 ± 14.7

126.0 ± 13.7

Four night shifts

110.9 ± 18.1

117.1 ± 17.2

116.1 ± 18.8

123.9 ± 12.6