The linguistic validation was carried out following the international guidelines [13]. First, the original ODSI developers (FO and SHO) were contacted for permission to use the instrument and invited to become involved in the translation and validation process.

Second, two native target language translators (PÜ, BBD) independently performed a forward translation of the ODSI from English into Turkish including original items, instructions, and response choices. Afterwards, the two translators discussed their translations and produced a combined version.

Third, after production of the combined version, both of two translators and the translation committee consisting of three geriatricians (GŞA, ME, CB) discussed the translation and agreed on a single reconciled version. In order to improve this version, a third translation from French to Turkish (forward translation SHO) was performed blindly. As a result, the first version of the ODSI Turkish for Türkiye was reached after some minor changes.

Fourth, a backward translation was performed by a translator who is a native speaker of English and bilingual in the target language.

Fifth, the translation committee reviewed and compared the backward translation and the original ODSI. They changed only two words in Turkish version to ensure the conceptual equivalence of the translation. Thus, after harmonization, the second version was created.

Sixth, the previous improved translation was applied face-toface to ten non-demented native Turkish speaker patients. The participants had no difficulty understanding and answering all three questions of the test. In other words, the cognitive debriefing was successful.

Seventh, the finalized translation is proofread to check for minor errors (spelling, grammatical, and/or other errors) which have been missed during the translation process.

Finally, this improved translation was adopted to conduct the reliability and validity study of the ODSI in Turkish language (Turkish version provided in Supplementary Materials in the online-only Data Supplement).

A total of 106 consecutive patients who were attending to the university hospital geriatric outpatient clinic were included in this study. Patients with dementia, delirium, known psychiatric diseases, using psychotropic drugs, and who were not able to speak Turkish were not included in the study.

All participants underwent comprehensive geriatric assessment. Age, gender, education, and living status were recorded. Geriatric syndromes including malnutrition, incontinence, osteoporosis, depression, polypharmacy, falls, insomnia, and other sleep related disorders were evaluated. Katz Activities of Daily Living (ADL) scale [14], Lawton Brody Instrumental Activities of Daily Living scale (Lawton-Brody) [15,16], Mini-Nutritional Assessment– short form (MNA-SF) [17], Mini-Mental State Examination (MMSE) [18], and Yesevage Geriatric Depression Scale short form [19] were administered to all patients.

Patients were asked a single question “Are you excessively sleepy during the day?” to state their daytime sleepiness as “never, rarely, regularly, or frequently.’’ They were enrolled in the group “EDS” when the answer was “regularly” or “frequently” and in the group “control” when it was “never” or “rarely” [20]. In addition, the ESS and the ODSI were filled in.

The study protocol was approved by the Hacettepe University Ethics Committee (GO 18/744-47). Informed consent was obtained from all individual participants included in the study.

The ESS is an 8-question scale developed by Johns [9] that assesses sleepiness in daily activities. For every question in the scale, ‘’0’’ points out no chance of sleepiness, “1,” “2,” and “3” indicate mild, moderate, and significant sleepiness. Total score range is 0–24 points and a cutoff >10 points is accepted to indicate EDS. The Turkish version of the ESS has been validated in 150 patients with sleep disorders [8].

The ODSI, composed of 3 standardized questions, is a short and easy-to-administer test that assesses daytime sleepiness. The ODSI is administered by a healthcare professional as an interview with the patients themselves and/or their relatives who observe the patient in activities of daily living. While administering the ODSI, the relatives/or proxies of the patients who were with them were asked whether “they agreed with the patient’s response” and whether “there was anything he/she wanted to add.’’ Responses to the 3 items are summed to yield a total score from 0 (non-sleepy) to 24 (extremely sleepy).

Question-1 helps to assess sleepiness or falling asleep in active situations or situations where a high level of stimulation is required such as washing, getting dressed, eating, talking, and driving. Because sleepiness during active situations is likely more unsafe, experts suggested adding 6 to the first item while keeping a “0” unchanged. Thus, scoring for the first item would be 0, 7 (1+6), 8 (2+6), etc., and first item scores would range from 0 to12.

Question-2 helps to assess sleepiness or falling asleep in passive situations or situations where a low level of stimulation is required such as reading, watching TV, listening to a conversation, and listening to music. The score range is 0–6.

Question-3 helps to estimate the average total duration of sleep during the day, including feeling sleepy, dozing off, and taking naps. The score range is 0–6.

In the study of 133 patients, 73 of whom were obstructive sleep apnea syndrome (OSAS), the ODSI sensitivity was found 0.842 (95% confidence interval [CI]: 0.624–0.945) and specificity was found 0.851 (95% CI: 0.761–0.911). The ODSI has demonstrated internal consistency and a reliability coefficient (Pearson and Spearman coefficients) of 0.70. The intra-class correlation (r=0.856, 95% CI: 0.796–0.902) and test-retest sessions (r=0.970, 95% CI: 0.898–0.991) were high. Receiver operating characteristic (ROC) curve analysis showed that a cutoff point of 6 is valuable for classifying EDS for older people [11].

In order to assess its test-retest reliability, the inventory was used twice in 13 patients seven days apart. For interrater reliability, the ODSI was performed on 11 patients by two geriatricians (PÜ, GŞA) who did not know each other’s scores in a different examination room on the same day.

The minimum sample size required to have an internal consistency above 70% and type 1 error level below 5% was found to be 90 for 3-item scale. The sample size was determined by PASS Power Analysis and Sample Size software program 11 (NCSS, LLC, Kaysville, UT, USA). Continuous variables were presented as mean±standard deviation for normally distributed variables and median (minimum–maximum) for skew distributed variables. Categorical variables were presented as number and frequency. The following procedures were used for the item analysis. Item scores were summarized using median and minimum–maximum values. In order to validate the consistency of the rating scale, inter-item correlations (Pearson and Spearman coefficients) and correlations between item scores and summated scale scores were evaluated. Interclass correlation coefficient (ICC) was used to examine test-retest reliability and interrater reliability. The construct validity was assessed by Spearman correlation analyses between the ODSI and the ESS. The accuracy of the test was measured by the area under the curve (AUC) from ROC curve analysis. The optimal cutoff score for detecting EDS (scored greater than 10 from the ESS) of the ODSI was assessed by the ROC curve analysis. Cohen’s kappa statistics (using a cutoff of the ESS >10) was calculated. Statistical analyses were performed by SPSS Statistics 23.0 program (IBM Corp., Armonk, NY, USA). A 5% type I error level was used to infer statistical significance.