Study design and participants

This cross-sectional study was conducted with a sample of 344 community members in Bangkok, Thailand. The inclusion criteria were as follows.

  • Individuals aged over 20 years

  • Those recovering from COVID-19

  • Living in Ratchathewi District, Bangkok, Thailand

Based on a former study, the ideal sample size for the item analysis is 10 participants for every item [17]. Specifically to reduce the error rate, the recommended optimal ratio is 20:1 for the participants to items ratio [18]. In the current study, the sample size was estimated to be 210–420 for the 21-item instrument. The actual sample size was within the estimated range, and a researcher collected the data from subjects that met the inclusion criteria.

Translation process

The researchers accessed the licensing authority at the University of Leeds, United Kingdom, for self-identification and requested permission to use the C19-YRS in Thailand. After obtaining approval, the research team began the translation process. They used a cross-cultural adaptation [19] as a guideline for translating the C19-YRS according to the approved recommendations. The original English version of the C19-YRS was forward-translated into the Thai language by two independent bilingual translators. One translator was an instructor with expertise in community health nursing and disaster (T1); the second translator was a physical therapist expert in cardiovascular and pulmonary rehabilitation (T2). A meeting was held to merge the drafts produced by the two translators for the purpose of forward-translation (T-12). Then, a second translator, with no healthcare background, back-translated the T-12 version into English while being blinded to the original version. This process was employed for a validity check and to determine the similarity of the content to the original version (T1).

Next, both the original and back-translated versions were reviewed in order to reach a consensus regarding the semantic and conceptual equivalence by an expert committee. The back-translated English draft was sent to its original developer following approval by the Leeds licensing authority in order to check the appropriateness of the cross-cultural equivalence. Using the content validity index, five expert individuals (two community health nursing specialists, two rehabilitation specialists, and one instrument development expert) evaluated the content validity of the C19-YRS preliminary translated Thai version (CVI). These experts were asked to rank each item on the basis of how appropriate and relevant the C19-YRS preliminary translated Thai version was. The CVI was 0.95, indicating that the contents were sufficiently valid and relevant [20].

The Thai version of the C19-YRS preliminary tool was pilot tested with 30 participants that had recovered from COVID-19 in Bangkok, and then was re-tested with a group of similar participants after two weeks. The correlation coefficient of the results over time was greater than 0.78, indicating good internal consistency [21]. Some modifications were made in order to make the translated Thai version easily understandable in the Thai context.


The C19-YRS was developed by Sivan and MDT rehabilitation professionals in 2021 [7, 22]. The scale was used to monitor the long-term COVID and the post-COVID-19 syndrome. The C19-YRS consisted of 25 items, starting with two opening questions, followed by 15 questions focusing on the main symptoms. Five questions concentrated on functional abilities and social roles, one question was related to perceived health status, one question was linked to family perspectives, and finally, one question addressed other symptoms not mentioned in the other questions. The major symptoms (n = 15) consisted of the following.

  • Breathlessness at rest, when dressing, or caused by walking up stairs

  • Coughs or throat discomfort

  • Changes in voice

  • Difficulty swallowing

  • Nutritional concern

  • Fatigue

  • Incontinence

  • Pain or discomfort

  • Difficulty with concentration

  • Short-term memory

  • Difficulty with planning

  • Anxiety or depression

  • PTSD

Further, the participants answered the following five “Yes” or “No” questions related to functional abilities and social roles: (a) communication, (b) mobility, (c) personal care, (d) activities of daily living, and (e) social roles. Answering “Yes” indicated that the participants experienced an adverse effect of COVID-19 regarding those symptoms and functional impairments. The participants were asked to rate the severity of their symptoms on a scale of zero to 10, and they were also asked to compare their symptoms concerning to how they felt prior to having COVID-19.

Regarding interpretation, the C19-YRS was divided into three subscales, consisting of symptom severity (15 items), functional ability (five items), and overall health (one item). The score for each symptom was divided into the three categories of mild (0 to 2), moderate (3 to 5), and severe (6 or higher). The total score for the symptom severity subscale ranged from zero to 150. The total score representing functional ability ranged from zero to 50, and the score for overall health ranged from zero to 10.

Data collection

The data collection process started after obtaining approval from the Institutional Review Board (IRB) Committee on Human Research. The data were collected between November 2021 and May 2022. The researcher contacted community leaders in Bangkok, described the study objectives, and sought their cooperation in securing contact information on potential participants. Two data collection methods were used, depending on the participants’ ability to use and access the Internet. In some cases, participants accessed the online questionnaire, and the researcher or coordinators provided a QR code to access it. The participants took approximately 15 min to answer the questionnaire by themselves. For the participants that were unable to access the online questionnaire, the researcher or study coordinators collected the data using a paper-based questionnaire.

Statistical analysis

The data were analyzed using the Statistical Package for Social Sciences (SPSS) for Windows, version 21. Missing data were excluded before the analysis. An overview of the participants’ characteristics was presented using descriptive statistics. Cronbach’s alpha coefficient was used to assess the internal consistency of the items, and item analyses were performed in order to assess the reliability of the instrument according to Ferketich’s study [21].

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