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. Author manuscript; available in PMC: 2019 Jan 2.
Published in final edited form as: J Clin Psychiatry. 2016 Jun;77(6):e726–e733. doi: 10.4088/JCP.15m10131

Table 2.

Calculating Expected Frequenices Per Clock Hour

1 2 3 4 5 6 7 8 9 10 11 12
Hour ATUS
% Awake1 		Scaled
% Awake2 		Expected
# Awake3 		Scaled
Expected
Awake4 		Observed
Frequency5 		Observed
%6 		Adjusted
%7 		Scaled
%8 		Standardized
Incidence
Ratio (SIR)9 		95% CI for SIR P
value
0:00 14.47% 0.89% 4971.74 316.22 1153 3.26% 23.19% 8.27% 3.65 (3.43, 3.86) <0.001
1:00 8.36% 0.53% 2954.17 187.89 1007 2.85% 34.09% 12.16% 5.36 (5.03, 5.70) <0.001
2:00 5.89% 0.37% 2080.76 132.34 949 2.69% 45.61% 16.27% 7.17 (6.72, 7.64) <0.001
3:00 5.34% 0.34% 1886.76 120.00 777 2.20% 41.18% 14.69% 6.47 (6.02, 6.94) <0.001
4:00 10.19% 0.65% 3600.73 229.02 690 1.95% 19.16% 6.83% 3.01 (2.79, 3.24) <0.001
5:00 21.89% 1.39% 7735.18 491.98 746 2.11% 9.64% 3.44% 1.52 (1.40, 1.62) <0.001
6:00 47.40% 3.01% 16746.51 1065.13 1030 2.92% 6.15% 2.19% 0.97 0.90, 1.02) 0.2918
7:00 69.92% 4.45% 24704.73 1571.29 1241 3.51% 5.02% 1.79% 0.79 (0.74, 0.83) <0.001
8:00 82.66% 5.26% 29206.87 1857.64 1548 4.38% 5.30% 1.89% 0.83 (0.79, 0.87) <0.001
9:00 89.80% 5.71% 31728.35 2018.01 1748 4.95% 5.51% 1.96% 0.87 (0.82, 0.90) <0.001
10:00 93.82% 5.97% 33149.08 2108.38 1814 5.13% 5.47% 1.95% 0.86 (0.82, 0.90) <0.001
11:00 95.63% 6.08% 33787.45 2148.98 2027 5.74% 6.00% 2.14% 0.94 (0.90, 0.98) 0.0081
12:00 96.34% 6.13% 34039.95 2165.04 2334 6.61% 6.86% 2.45% 1.08 (1.03, 1.12) 0.001
13:00 95.92% 6.10% 33891.12 2155.57 1701 4.81% 5.02% 1.79% 0.79 (0.75, 0.82) <0.001
14:00 96.01% 6.11% 33922.25 2157.55 1825 5.17% 5.38% 1.92% 0.85 (0.80, 0.88) <0.001
15:00 96.46% 6.13% 34079.52 2167.55 1871 5.30% 5.49% 1.96% 0.86 (0.82, 0.90) <0.001
16:00 96.81% 6.16% 34204.99 2175.53 1828 5.17% 5.34% 1.91% 0.84 (0.80, 0.87) <0.001
17:00 97.26% 6.19% 34365.28 2185.73 1816 5.14% 5.28% 1.88% 0.83 (0.79, 0.86) <0.001
18:00 97.43% 6.20% 34424.29 2189.48 1768 5.00% 5.14% 1.83% 0.81 (0.77, 0.84) <0.001
19:00 96.80% 6.16% 34200.01 2175.22 1718 4.86% 5.02% 1.79% 0.79 (0.75, 0.82) <0.001
20:00 93.09% 5.92% 32891.02 2091.96 1551 4.39% 4.72% 1.68% 0.74 (0.70, 0.77) <0.001
21:00 79.91% 5.08% 28234.86 1795.82 1469 4.16% 5.20% 1.86% 0.82 (0.77, 0.86) <0.001
22:00 53.28% 3.39% 18824.30 1197.28 1444 4.09% 7.67% 2.74% 1.21 (1.14, 1.26) <0.001
23:00 27.96% 1.78% 9879.86 628.39 1277 3.61% 12.93% 4.61% 2.03 (1.92, 2.14) <0.001
SUM: 1572.24% 100.00% 555509.83 35332 35332 100.00% 280.37% 100.00%
1

The proportion of the population awake at each hour based on ATUS.

2

Proportions, divided by the total of all proportions (value from column 2, divided by the sum of all values from column 2). This scales each proportion so that they all sum to 100%.

3

Values from column 2, multiplied by the total N=35332. This represents the number of individuals from the sample expected to be awake at each hour.

4

Values from column 4, divided by the total of column 4. This normalizes all values to a 100% scale.

5

The observed number of suicides at each clock hour, from NVDRS.

6

The proportion of suicides occurring at each clock hour compared to the entire sample (obtained by dividing each value from column 6 by the total N=35332.

7

The proportion of suicides occurring at each clock hour compared to the amount of the sample that is estimated to have been awake at that time (obtained by dividing the number of observed suicides from column 6 by the expected # awake in column 4).

8

Values from column 8, divided by the sum of all values from column 8. This normalizes proportions so they all add up to 100.

9

SIR computed by dividing the observed frequency from column 6 (i.e., observed) by the scaled number expected awake from column 5 (i.e., expected).

10

95% Confidence Interval (95%CI) computed around the SIR.

11

P value for SIR