Participants
This study was conducted as part of the study project of “Well-Living for Well-Being” organized by the Consortium for Applied Neuroscience (CAN), Tokyo, Japan. Participants were recruited from a pool of approximately 50,000 individuals registered in the Human Information Database maintained by the NTT DATA Institute of Management Consulting, Inc., Tokyo, Japan. Interested individuals were directed to an online form outlining the study procedures, schedule, eligibility criteria (full-time employment, Japanese nationals, working in Japan on weekdays, age between 30 and 49, ability to maintain a journal and respond to questionnaires via smartphone), and the compensation to be paid upon completion (32,000 yen). Candidates meeting all requirements were asked to provide their contact information, name, and gender. In adherence to the principles outlined in the Declaration of Helsinki, candidates who opted to participate were required to complete and submit an online consent form. The study received approval from the Shiba Palace Clinic Ethics Review Committee in Tokyo, Japan (approval number: 150926_rn_33852).
An a priori power analysis was conducted using G*Power [31, 32] for a two-way repeated measures ANOVA (within-between interaction), with power set at 0.80, a medium effect size of 0.25, an alpha error rate of 0.05, two groups, three measurements, a correlation among repeated measures of 0.50, and a nonsphericity correlation value of 0.75. The analysis indicated that a minimum total sample size of 34 participants was required. We recruited a total of 100 company employees who met the eligibility criteria, evenly divided between male and female, exceeding the minimum required sample size. All participant communication, including online forms, assessments, and journaling, was conducted in Japanese.
The participants in the experiment came from a wide range of industries, including sales, consulting, IT, manufacturing, logistics, and finance. Their job titles were distributed as follows, in ascending order of managerial position: staff-level employee (57.14%), supervisor (28.57%), department manager (5.71%), and general manager (8.57%). Out of the 100 participants recruited for the journal intervention experiment, 91 individuals wrote journal entries during the study period (45 in the gratitude journal group and 46 in the daily life journal group). Regarding responses to psychological measurements, 74 participants completed the assessment at T1 (right before the intervention, 36 in the gratitude journal group, 38 in the daily life journal group), and 70 individuals completed both T1 and T2 (immediately after the intervention, 35 in each group). All experimental participants were subsequently emailed a delayed follow-up questionnaire at T3 (approximately 1.5 months after the intervention). Of the participants who completed the questionnaires at both T1 and T2, 68 individuals also completed the assessment at T3 (35 in the gratitude journal group and 33 in the daily life journal group).
Procedure
This study was part of a two-month project organized by the CAN, aimed at exploring innovative ways to apply foundational positive psychology research to societal contexts. During this project (October 14th to December 19th, 2022), participants took part in several different studies. The gratitude journal intervention took place over the course of 12 days (October 24th to November 4th, 2022), during which no other experiments were conducted.
A few days before the experiment, participants received an email with instructions for accessing a custom-developed web application, including an individual account name and password. They were asked to log in via the provided URL and complete psychological questionnaires (see “Materials” section). Participants were then randomly assigned to either the gratitude journal group (experimental) or the daily life journal group (control) while ensuring a balanced distribution of gender across groups.
For 12 days, participants received daily email reminders with a URL to the web application, prompting them to write journal entries via their smartphones. Participants in the gratitude journal group were instructed to “Please write down at least one thing (ideally around three) you felt grateful for today. If nothing comes to mind, you may recall something you felt grateful for recently (within the past year).” Participants in the daily life journal group were instructed to “Please write down at least one thing (ideally around three) that happened today.” Example entries included expressing gratitude for a colleague’s help (gratitude journal) and describing a visit to a bakery (daily life journal). Each session allowed up to five free-writing spaces, with no limit on daily access. Participants could submit additional entries if desired. While participants were free to write as much or as little as they wished, entry length or word count was not actively monitored during the data collection period. Immediately after the 12-day intervention and 1.5 months later, they completed the same psychological scales as those administered at the pre-intervention stage.
Materials
Work engagement
Work engagement was assessed using the 9-item Utrecht Work Engagement Scale (UWES) [33], which measures workers’ positive mental states towards their work and is considered the positive counterpart to burnout. The UWES consists of three dimensions: Vigor, Dedication, and Absorption. While these dimensions can be analyzed separately, the UWES manual recommends using the total score when focusing on overall work engagement, due to the high intercorrelations observed among the three dimensions [34]. Our correlation analyses confirmed this pattern (Vigor-Dedication r = 0.856, Vigor-Absorption r = 0.782, and Dedication-Absorption r = 0.866, all p < 0.001), consistent with the values reported in the UWES manual [34]. Based on this, we primarily used the total UWES scores to examine the effect of gratitude journaling on overall work engagement, as our focus was on engagement as a unified construct rather than its components. We used the Japanese version of the UWES (UWES-J) [35, 36], which includes nine items (three per dimension). Participants rated each item (e.g., “At my work, I feel bursting with energy”) on a 7-point scale from 0 (Never) to 6 (Always/Every day). Cronbach’s alpha for the pre-intervention sample indicated good internal consistency (Total alpha = 0.945, Vigor alpha = 0.89, Dedication alpha = 0.87, and Absorption alpha = 0.85).
Work motivation
Work motivation was assessed using the 36-item Work Motivation Questionnaire in Japanese Organizations (referred to as WM-J) [37], which was developed specifically for Japanese respondents based on the work motivation scale by Barrick et al. [38]. The WM-J measures four aspects of work motivation: Competitive, Cooperative, Learning, and Accomplishment-Oriented motivation, with each dimension assessed by nine items. Participants rated each item on a 5-point scale from 1 (strongly disagree) to 5 (strongly agree). Cronbach’s alpha for the pre-intervention sample indicated high internal consistency: Competitive alpha = 0.92, Cooperative alpha = 0.90, Learning alpha = 0.93, and Accomplishment-Oriented alpha = 0.91.
Gratitude disposition
Gratitude disposition was assessed using the Gratitude Questionnaire (GQ-6) [39], which measures individuals’ tendency to experience gratitude. Participants rated statements such as “I have so much in life to be thankful for” on a 7-point scale, from 1 (strongly disagree) to 7 (strongly agree). The GQ-6 has been translated into Japanese, and its validity has been confirmed for Japanese individuals [40,41,42]. However, Shiraki [41] conducted a factor analysis on the Japanese version and found that the sixth item (“Long amounts of time can go by before I feel grateful to something or someone”) had a factor loading lower than 0.4, while the remaining five items showed loadings greater than 0.4, supporting a one-factor structure for the Japanese version. Another study also confirmed the suitability of this five-item version [42]. Therefore, we excluded the sixth item when assessing participants’ gratitude disposition in this study as well. This scale will be referred to as GQ-J. The Cronbach’s alpha for the pre-intervention sample was 0.87, indicating good internal consistency.
Perspective taking
The Perspective Taking (PT) Scale is part of the Interpersonal Reactivity Index (IRI) [43, 44] and assesses individuals’ tendency to adopt the perspectives of others. The original scale consists of seven items, such as “Before criticizing somebody, I try to imagine how I would feel if I were in their place,” rated on a 0 to 4 scale (0 = does not describe me well to 4 = describes me very well). In this study, we used the Japanese version of the scale [45], which employs a five-point scale from 1 (strongly disagree) to 5 (strongly agree). Cronbach’s alpha for the pre-intervention sample was 0.72.
Life satisfaction
The 5-item Satisfaction With Life Scale (SWLS) [46] was used to assess participants’ overall life satisfaction. The SWLS is widely used as a measure of the cognitive component of subjective well-being [47]. Respondents rated statements such as “In most ways my life is close to my ideal” on a 7-point scale from 1 (strongly disagree) to 7 (strongly agree). We employed the Japanese translation of the SWLS available on the website of the original study’s first author. Cronbach’s alpha for the pre-intervention sample was 0.89, indicating good internal consistency.
Psychological well-being
Psychological well-being was assessed using the 42-item version of the Psychological Well-Being Scale (PWBS) [48], which measures six dimensions: autonomy, environmental mastery, personal growth, positive relations with others, purpose in life, and self-acceptance (7 items each). We used the Japanese translation of the scale [49]. Items were intermixed and rated on a 7-point scale from 1 (strongly disagree) to 7 (strongly agree). The Cronbach’s alphas for the pre-intervention sample in this study were: autonomy alpha = 0.75, environmental mastery alpha = 0.74, personal growth alpha = 0.80, positive relations with others alpha = 0.72, purpose in life alpha = 0.62, and self-acceptance alpha = 0.80, consistent with findings from the Japanese development study [49].
Personality traits
Personality traits were assessed using the Neuroticism-Extroversion-Openness Five-Factor Inventory (NEO-FFI), a measure of the Big Five personality traits. The NEO-FFI consists of 60 items, with 12 items per dimension: Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness. We used the Japanese translation of the NEO-FFI [50]. Cronbach’s alphas for the pre-intervention sample were: Neuroticism alpha = 0.88, Extraversion alpha = 0.84, Openness alpha = 0.66, Agreeableness alpha = 0.70, and Conscientiousness alpha = 0.77.
Experimental schedule
All psychological measures (UWES/WM-J/GQ-J/PT/SWLS/PWBS/) except NEO-FFI were assessed at three time points to evaluate the effects and persistence of the 12-day journal intervention. Assessments were conducted just before the intervention (T1: October 20th to 23rd), immediately after the intervention (T2: November 4th to 7th), and approximately 1.5 months after the intervention (T3: December 21 st to 25th). The NEO-FFI was administered at T1. Participants were informed about the schedule for the three psychological measurements during recruitment. However, they were unaware of the different groups in the journaling experiment and were not informed of the research hypothesis.
Analysis methods
All statistical analyses were conducted using IBM SPSS Statistics (Version 29) unless stated otherwise. Group differences were examined by analyzing the dependent variable using two-way repeated measures analysis of variance (rm-ANOVA). Adjustments for degrees of freedom were made using Greenhouse-Geisser estimates of sphericity (Mauchly’s sphericity test) as needed. Statistical significance was set at an alpha level of less than 0.05. Post-hoc tests were conducted when appropriate and adjusted for multiple comparisons using the Bonferroni correction if applicable. All textual analyses of journal entry were conducted using KH Coder, a computer software package for quantitative content analyses [51, 52].
To examine the effects of the gratitude journal intervention, we conducted a two-way repeated measures ANOVA with time (T1, T2, and T3) as the within-subject factor and journal group (gratitude journal vs. daily life journal) as the between-subject factor for each one of the outcome measures.