Research Letter | Medical Education

Association Between Resident Duty Hours and Self-study TimeAmong Postgraduate Medical Residents in Japan
Kazuya Nagasaki, MD; Yuji Nishizaki, MD, MPH, PhD; Tomohiro Shinozaki, MPH, PhD; Hiroyuki Kobayashi, MD, PhD; Yasuharu Tokuda, MD, MPH

Introduction
Sufficient self-study time (SST) for postgraduate residents is important for their professional

Author affiliations and article information arelisted at the end of this article.

development.1,2 Self-study time has a positive linear association with the acquisition of clinicalknowledge.3 In 2024, duty-hour (DH) restrictions will be implemented in Japan for postgraduate
residents; therefore, the association of DHs with resident study habits must be evaluated.4 In the US,
DH restrictions have had minimal or no association with resident SST.5 The objective of this study
was to assess the association between DHs and resident SST using information from the General
Medicine In-Training Examination (GM-ITE) survey in Japan.

Methods
We conducted a cross-sectional survey among 5590 postgraduate residents across Japan who hadtaken the GM-ITE from January 20 to 26, 2020.6 This examination evaluates the acquisition ofclinical knowledge. Participants were asked about mean DHs and SST, as well covariates including
sex, postgraduate year, the number of emergency department duties, and the mean number of
inpatients in their care. All participants signed a consent form. The Ethics Review Board of Mito
Kyodo General Hospital approved the study. This study followed the Strengthening the Reporting ofObservational Studies in Epidemiology (STROBE) reporting guideline.

Table. Proportion of Self-study Time Categories in Each Duty-Hour Category of 5590 Participants
Categorized by duty hours, No. (%)aa

Self-study time,
min/dTotal, No. (%)(N = 5590)

Category 1(n = 133)

Category 2(n = 514)

Category 3(n = 827)

Category 4(n = 832)None

239 (4.3)

10 (7.5)

17 (3.3)

28 (3.4)

35 (4.2)

36 (3.4)

29 (3.8)

29 (4.3)

55 (6.8)

1-302067 (37.0)

73 (54.9)

253 (49.2)

323 (39.1)

314 (37.7)

374 (35.7)

245 (32.5)

214 (31.7)

271 (33.6)

31-60

2330 (41.7)

33 (24.8)

196 (38.1)

352 (42.6)

353 (42.4)

435 (41.5)

360 (47.7)

294 (43.5)

307 (38.0)

61-90

788 (14.1)

14 (10.5)

43 (8.4)

104 (12.6)

107 (12.9)

170 (16.2)

100 (13.3)

112 (16.6)

138 (17.1)≥91

166 (3.0)

3 (2.3)5 (1.0)20 (2.4)

23 (2.8)

32 (3.1)

20 (2.7)

27 (4.0)36 (4.5)

Resident duty hours per week comprised 8 categories: category 1 (<45 hours), category
2 (ⱖ45 to <50 hours), category 3 (ⱖ50 to <55 hours), category 4 (ⱖ55 to <60 hours),

Category 5(n = 1047)

Category 6(n = 754)

Category 7(n = 676)

Category 8(n = 807)

category 5 (ⱖ60 to <65 hours), category 6 (ⱖ65 to <70 hours), category 7 (ⱖ70 to<80 hours), and category 8 (ⱖ80 hours).

Figure. Association Between Resident Duty Hours and Self-study Time (SST) of 5590 Participants
Favorsshorter SST

OR (95% CI)

Favorslonger SST

P value

Variable
Duty hours
Category 1

0.47 (0.33-0.66)<.001

Category 2

0.61 (0.52-0.73)<.001

Category 3

0.86 (0.73-1.01).07

Category 4

0.85 (0.72-1.01).07

Category 5

1 [Reference]

Category 6

1.00 (0.86-1.18).96

Category 7

1.12 (0.95-1.32).18

Category 8

0.98 (0.82-1.18)

.83
0.3

0.4

0.6

0.8

1.0

OR (95% CI)

1.2

1.4

Resident duty hours per week comprised the following
8 categories: category 1 (<45 hours), category 2 (ⱖ45to <50 hours), category 3 (ⱖ50 to <55 hours),
category 4 (ⱖ55 to <60 hours), category 5 (ⱖ60 to<65 hours), category 6 (ⱖ65 to <70 hours), category 7(ⱖ70 to <80 hours), and category 8 (ⱖ80 hours),
adjusted for sex, postgraduate year, the numbers ofmonthly emergency department duties, and mean
number of inpatients in residents’ care. Category 5 was
set as a reference. OR indicates odds ratio.

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Resident Duty Hours and Self-study Time Among Postgraduate Medical Residents

The dependent variable was SST per day, which comprised 5 categories (none, 1-30, 31-60,61-90, and ⱖ91 minutes). The independent variable was DHs per week. This variable was divided into
8 categories as follows: category 1 (<45 hours), category 2 (ⱖ45 to <50 hours), category 3 (ⱖ50 to<55 hours), category 4 (ⱖ55 to <60 hours), category 5 (ⱖ60 to <65 hours), category 6 (ⱖ65 to <70hours), category 7 (ⱖ70 to <80 hours), and category 8 (ⱖ80 hours).
We examined the association between resident SST and DHs using a proportional odds
regression analysis (ie, an ordered logistic model with a cumulative logit link) with adjustment.
Category 5 was set as a reference. We excluded participants from the analysis who did not provide
responses for SST or DHs. Hospital variability was accounted for by cluster-robust variance using
generalized estimating equations. All analyses were conducted using SAS, version 9.4 (SAS InstituteInc). All P values are 2-sided without setting significance level to show compatibility between dataand null association under the models.

Results
Of 6164 residents, 5590 at 528 hospitals were included in the analysis. Of the included residents,2837 (50.8%) were in their first postgraduate year and 1769 (31.6%) were women. Their SSTs wereas follows: 1 to 30 minutes, 2067 residents (37.0%); 31 to 60 minutes, 2330 residents (41.7%); 61 to
90 minutes, 788 residents (14.1%); 91 minutes or longer, 166 residents (3.0%); and none, 239residents (4.3%). They reported their DHs as follows: category 1, 133 residents (2.4%); category 2,514 residents (9.2%); category 3, 827 residents (14.8%); category 4, 832 residents (14.9%); category
5, 1047 residents (18.7%); category 6, 754 residents (13.5%); category 7, 676 residents (12.1%); andcategory 8, 807 residents (14.4%). The Table shows the distribution of SST categories in each DH
category.
After adjustment for sex, postgraduate year, the number of emergency department duties, andthe number of inpatients in their care, the resident SST was shorter for categories 1 to 4 than for
category 5 (Figure). In contrast, we observed little or no differences in SST between categories 6 to8 and category 5.

Discussion
In this study, postgraduate residents with DHs less than 60 hours per week had a shorter SST thanthose with DHs between 60 and 65 hours per week. This result indicated that extra time duringresidency may not necessarily be associated with more SST. It is possible that less-motivatedresidents may have chosen hospitals with shorter DHs. Also, the DH restrictions in Japan may run therisk of shortening resident SST. Providing online educational resources and conducive learning
environments in hospitals may improve resident study habits.5
Our study had the potential for selection bias. Because the GM-ITE is voluntary for training
hospitals, approximately one-third of residents in Japan participated in this study. In 2024, when DH
restrictions begin in Japan, each residency program must encourage residents to secure more SST
to maintain resident quality.

ARTICLE INFORMATION
Accepted for Publication: January 14, 2021.
Published: March 5, 2021. doi:10.1001/jamanetworkopen.2021.0782
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Nagasaki Ket al. JAMA Network Open.
Corresponding Author: Yuji Nishizaki, MD, MPH, PhD, Department of Medical Education, Juntendo University
School of Medicine, Tokyo, Japan, 2-1-1 Hongo Bunkyo-ku, Tokyo 113-8421, Japan (ynishiza@juntendo.ac.jp).

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Resident Duty Hours and Self-study Time Among Postgraduate Medical Residents

Author Affiliations: Department of Internal Medicine, Mito Kyodo General Hospital, University of Tsukuba,Ibaraki, Japan (Nagasaki, Kobayashi); Department of Medical Education, Juntendo University School of Medicine,Tokyo, Japan (Nishizaki); Department of Information and Computer Technology, Faculty of Engineering, Tokyo
University of Science, Tokyo, Japan (Shinozaki); Muribushi Okinawa for Teaching Hospitals, Okinawa,
Japan (Tokuda).
Author Contributions: Dr Shinozaki had full access to all of the data in the study and takes responsibility for theintegrity of the data and the accuracy of the data analysis.
Concept and design: Nagasaki, Nishizaki, Shinozaki, Tokuda.
Acquisition, analysis, or interpretation of data: Nagasaki, Nishizaki, Shinozaki, Kobayashi.
Drafting of the manuscript: Nagasaki, Shinozaki, Kobayashi, Tokuda.
Critical revision of the manuscript for important intellectual content: Nishizaki, Shinozaki.
Statistical analysis: Shinozaki.
Supervision: Nishizaki, Kobayashi, Tokuda.
Conflict of Interest Disclosures: Dr Nagasaki reported receiving personal fees and an honorarium from the Japan
Organization of Advancing Medical Education (JAMEP) as a General Medicine In-Training Examination (GM-ITE)
reviewer, outside the submitted work. Dr Nishizaki reported receiving personal fees from JAMEP and anhonorarium from JAMEP as the GM-ITE project manager outside the submitted work. Dr Kobayashi reported
receiving personal fees and an honorarium from JAMEP for a lecture outside the submitted work. Dr Tokuda
reported being the director of JAMEP. No other disclosures were reported.
Disclaimer: The JAMEP was involved in collecting and managing data as the GM-ITE administrative organization.
The JAMEP had no role in the design and conduct of the study; data analysis and interpretation; preparation,review, or approval of the manuscript; and the decision to submit the manuscript for publication.
Additional Contributions: We thank members of JAMEP for their assistance. The authors would like to thankEnago (www.enago.jp) for the English language review.
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