Lower urinary tract symptoms (LUTS) are a complex group of symptoms that result from diseases and medical conditions affecting the bladder and urethra. The International Continence Society (ICS) classifies LUTS into 3 categories—storage, voiding, and postmicturition symptoms [1]. LUTS are highly prevalent in the general population, with a prevalence of 64.3%- 76.3% reported in previous studies [2,3]. Severe LUTS are negatively associated with quality of life (QoL) [4]; thus, proper management of LUTS is important for a patient’s welfare.

LUTS are associated with urologic diseases, such as benign prostatic hyperplasia (BPH) and overactive bladder (OAB) [5]. BPH is predominantly characterized by the proliferation of smooth muscle and epithelial cells of the prostate transition zone [6], which is one of the most common urologic problems that cause LUTS in the elderly population [5,7]. OAB is clinically defined by the presence of urinary urgency, mostly cooccurring with urinary frequency and nocturia with or without urge urinary incontinence (UUI) [8,9]. Approximately 10% of worldwide general population have OAB symptoms, and it increased to 20% in 2018 [10].

To evaluate and diagnose LUTS, patients’ medical history, laboratory tests, questionnaires, and function assessment tools, including uroflowmetry, frequency-volume chart, and urodynamic study, were analyzed [11-13]. Owing to the subjective nature of LUTS, the objective measurement of subjective symptoms by patient-reported outcome measurement tools (PROMs) is essential in the management of urologic disease and clinical studies [14]. Therefore, choosing appropriate questionnaires in a clinical trial is extremely important to determine the success or failure of clinical studies [15].

Numerous PROMs have been developed worldwide; however, none of the guidelines showed how to apply optimal PROMs for specific symptoms or diseases. In this review, we have explained previously established procedures for translation and linguistic validation of developed PROMs for other languages and suggested validated PROMs for common urologic diseases.

In most cases, using a formerly translated and validated questionnaire is a practical method to perform clinical studies and measure patient-reported outcomes (PROs). If there are no optimal questionnaires available in the Korean language, we can develop an in-house questionnaire or translate questionnaires to the Korean language. The development of the novel in-house questionnaire has many obstacles, owing to the difficulty in obtaining the validity, reliability, responsiveness, and interpretability of each statement [16]. Each process requires multiple efforts and time for in-house development using preexisting and already validated questionnaires might be a reasonable alternative. Moreover, using a multiculture, validated questionnaire is beneficial for a multinational, multicenter clinical trial design [15]. Numerous questionnaires have been developed and validated worldwide; thus, translating questionnaires in Korean is more effective than developing in-house questionnaires.

The translated version of the questionnaire does not guarantee equivalent accuracy in collecting patients’ responses to the original version. A well-translated questionnaire provides the same meaning and uses appropriate idioms for each language [17] however, it is not easy. To develop a cross-cultural equivalent of the translated and original version of the questionnaire, linguistic and psychometric validation of the translated questionnaire is essential.

The first process, linguistic validation, has to follow the principles of good practice for translation and cultural adaptation (TCA) process for PROMs, which was announced by the International Society for Pharmacoeconomics and Outcomes Research task force [18]. The TCA framework for PROMs consists of 8 core steps: preparation, forward translation, reconciliation, back translation, harmonization, cognitive debriefing, proofreading, and final reporting. In the preparation phase of the TCA, the project manager should contact the copyright holder for approval of the use and translation of the questionnaire.

Forward translation and back translation must be performed by at least 2 independent translators: a professional translator and a native speaker of the target language and source language (Fig. 1). The reconciliation phase resolves the discrepancy between the forward translators by an independent bilingual, who was not exposed to the forward translation process. The most important part of this process is the reconciliation decision reviewed by the project manager. Back translation is a quality control step performed by at least one backward translator. Harmonization is essential in the TCA process, intensively reviewing and obtaining the equivalent of the source and translated versions of questionnaires by harmonization meetings with the project manager, in-country consultant, and translators.

Cognitive debriefing is the pilot testing of the translated questionnaire to at least 5–8 responders. The project manager assesses face validity, convergent validity, discriminant validity, responsiveness, test-retest, and internal consistency of each respondent. In this step, the project manager assesses that patients exactly understand the meaning of the contexts using responder’s opinion and decide whether to revise the translated questionnaire. After reviewing and proofreading each step, the final version of the translated questionnaire is verified for use in the target country with the same quality of that of the source country questionnaire.

In the second phase of validation, psychometric validation is a more complex process for obtaining validity and reliability of the questionnaire (Fig. 2) [19]. The validity and reliability of the questionnaire need to be verified before application in clinical research. Validity refers to the accuracy, and reliability refers to the consistency of the instrument for evaluating symptom scores. The establishment of validity should be conducted in several ways, including assessing (1) construct, (2) content, (3) criterion, and (4) face validity.

Construct validity represents the relationship between the questionnaire score and the underlying hypothesis [20-22]. Content validity, also known as logical validity, indicates that the items of the questionnaire measure all components that are supposed to be measured [20]. Criterion validity measures the relationship between the novel assessment tool and the current gold standard or another validated tool [22]. Face validity is the subjective view of responders’ symptoms or patients’ QoL, which is also supposed to be measured.

Reliability is another component of the psychometric performance measure of the developed questionnaire. Internal reliability refers to the consistency within the tests, which can be measured using statistical methods of Cronbach’s alpha [20]. External reliability refers to the consistency between the tests, which can be assessed by test-retest reliability and interrater reliability [19,20]. After confirming linguistic validity and psychometric validity, the foreign language questionnaire is fully validated.

From the late 1990s to early 2000, several novel anticholinergic drugs were introduced in the market and multinational, multicenter clinical trials were actively performed. The desire of the Korean Continence Society to participate in clinical trials on patients with OAB has increased. To quantify patients’ subjective LUTS and their QoL for multinational clinical trials, validated Korean versions of international LUTS questionnaires were a prerequisite. However, no questionnaires had been validated by the society, and there was no experience of conducting validation of the questionnaires. In the early 2000s, Dr. SeungJune Oh was interested in validating the Incontinence Quality of Life (I-QOL) questionnaire on a personal level and directly contacted Health Research Associates Inc., Mountlake Terrace, WA, USA to conduct the full linguistic validation process to complete the Korean version of the I-QOL [23]. I-QOL was the first fully validated Korean version of the urinary incontinence questionnaire that was validated using a formal professional validation process. Based on his experience with the full linguistic validation process, Dr. Oh suggested to the Korean Continence Society (KCS) that he would organize taskforce teams to validate the Bristol Female Lower Urinary Tract Symptom (BFLUTS) [24] and King’s Health Questionnaire (KHQ) [25] in Korean. The Korean versions of the KHQ and BFLUTS questionnaires are the first questionnaires that were linguistic and psychological validated by a multicenter study with the involvement of the KCS. Since then, validation studies of many other questionnaires initiated by Dr. Oh have also been conducted at the society or personal level. Consecutively, until the late 2000s, many international questionnaires required for clinical research have been validated in Korean, such as OAB questionnaire (OAB-q) [26], International Consultation on Incontinence Questionnaire (ICIQ), ICIQ-OAB, ICIQ for nocturia (ICIQ-N), ICIQ for male LUTS (ICIQ-MULUTS), Interstitial Cystitis Symptom Index (ICSI), and Interstitial Cystitis Problem Index (ICPI) [27], Urgency Perception Score (UPS) [28], Patient Perception of Bladder Condition (PPBC), Indevus Urgency Severity Scale (IUSS) [28], and OAB symptom score (OABSS) [29]. Since 2010, Korean versions of Patient Perception of Intensity of Urgency Scale (PPIUS), Pelvic Pain and Urinary/Frequency (PUF) [30], Urinary Tract Infection Symptoms Assessment (UTISA), Benefit, Satisfaction, and Willingness to Continue (BSW) [31], Overactive Bladder Satisfaction with Treatment Questionnaire (OAB-SAT-q) [32], and Expanded Prostate Cancer Index Composite for Clinical Practice (EPIC-CP) have been validated. The validated questionnaires obtained through this process played a decisive role in upgrading the level of clinical research on lower urinary tract dysfunction in Korean academic society.

Currently, there are approximately 30 available questionnaires for Korean patients with LUTS and neurogenic bladder (Table 1). The questionnaires focus on (1) objectifying the subjective symptoms, (2) scoring the degree of discomfort, and (3) assessing QoL and satisfaction. Most translated questionnaires are linguistically but not psychometrically validated. All questionnaires were freely accessible on the “Korean Continence Society (KCS)” official website (http://www.kcsoffice.org).

There were several issues regarding the interpretation of the questionnaire results. First, most questionnaires used a Likert scale, which is one of the most widely used psychometric scales to measure the responders’ attitude by several degrees of agreement with a statement. The Likert scale has an innate risk of bias that the researcher should be cautious of before analysis. If the variables show biased high estimates, patients tend to answer only low scores only (floor effect). In contrast, if the variables show biased low estimates, patients tend to answer high scores only (ceiling effect). Despite the changes in the independent variables, the changes in the dependent variable are not measurable, considering the ceiling or floor effect. In this situation, it is difficult to analyze the distribution of each degree because the score distribution is too low or too high. Therefore, the investigators must consider consistency and reliability before and after the tests for control and experimental groups and modify the statement for analysis.

Second, previous studies have shown that symptom scores and QoL do not directly reflect the severity of disease status. For example, BPH symptom scores do not accurately reflect the severity of LUTS, and several studies comparing questionnaire scores and urodynamic findings showed low correlations with urination muscle activity and bladder outlet obstruction [63-65].

In this review, we have summarized the established validation processes of the foreign language questionnaire before clinical use and explained the currently available questionnaires in Korean for LUTS. It is important to clearly determine the characteristics and limitations of each LUTS questionnaire to select the appropriate questionnaire for the clinical trial.