Knee Osteoarthritis (OA) is one of the most common joint diseases with chronic low-severity inflammation. 80% of individuals with knee OA have limited movements; It was found that 25% of them could not do their daily work. In addition, it has been shown that the quality of life of individuals with OA is lower compared to healthy individuals. This showed that measuring and reporting quality of life should be mandatory in clinical studies conducted in individuals with knee OA. It was stated that the most frequently used general scales in the evaluation of quality of life in these individuals were SF-36 or SF-12. It takes a long time for the SF-36 to be filled by individuals, which creates a disadvantage for both patients and clinicians. Developed as a shorter alternative to SF-36, SF-12 has also been shown to give similar results to SF-36 in individuals with knee OA who have undergone total knee arthroplasty. However, the psychometric properties of SF-12 in individuals with knee OA have not been examined. The purpose of this study is to examine whether SF-12 is valid and reliable in individuals with knee OA and to determine the minimum detectable change (MDC) value.

Forty volunteers aged 40 years and older diagnosed with knee OA will be included in the study. First, individuals will be informed about the study in detail, and signed informed consent form will be obtained from individuals who agree to participate in the study. First of all, the demographic information of the individuals will be recorded. Chronic diseases and continuous drug use will be questioned. Individuals' quality of life will be evaluated with the SF-12 and SF-36 scales, and their functional status will be evaluated with the WOMAC score. All scales will be filled once, but the second evaluation for the test-retest reliability (intra-rater reliability) of the SF-12 scale will be repeated one week later. In our study, the sample size was determined by using a web-based sample size calculation application specially developed for reliability-validity studies. In this application, hypothesis testing was performed according to ICC values. The minimum acceptable reliability (ICC) was 0.65 and the expected reliability from the study was 0.85. When the significance level of the study (α) was determined as 0.05 and the power of the study (1-β) was determined as 80%, and considering the probability that 10% of the individuals participating in the study could exit the study, it was found that the minimum sample size to be taken for the study should be 40 people. Jamovi 2.3.28 program will be used in the statistical analysis of the data. Variables determined by measurement will be expressed as mean ± standard deviation (X ± SD), percent (%) will be calculated for variables determined by counting. The normal distribution will be evaluated by examining both visually (Histogram and Q-Q plots) and statistical techniques (Kolmogorov Smirnov test, Skewness and Kurtosis values). Criterion-releated validity of SF-12 will be evaluated by its subtype, concurrent validity, and its correlation with WOMAC and SF-36 scales will be evaluated. Pearson correlation test will be applied when the correlation normal distribution conditions are met, and Spearman correlation test will be applied if not. Correlation coefficient level will be considered as <0.3 low, 0.3- 0.5 medium, >0.5 strong. In the reliability test of the SF-12 scale, test-re-test will be applied for the stability of the scale, and intra-class correlational coefficients (ICC) will be calculated. ICC values of 0.5-0.75 will indicate moderate reliability, 0.75-0.9 good reliability, and >0.9 excellent reliability. In order to determine the internal consistency of the scale, internal consistency coefficients (Cronbach's alpha) will be calculated. It will be at an acceptable level when Cronbach's alpha is >0.7. Absolute reliability will be determined by calculating the standard error of measurement (SEM) to ensure the accuracy of the measurement. The SEM will be used to calculate the smallest detectable change at the 95% confidence level (MDC95) and will be calculated as: MDC95=SEM × 1.95 × √2. In all statistics, the "p" significance value will be taken as 0.05.

Inclusion Criteria:

• 40 years and older,
• Radiological and clinical diagnosis of knee OA,
• Volunteering to participate in the study,
• Ability to read and write

Exclusion Criteria:

• Having problems with cooperation or cognitive impairment,
• Previous total knee arthroplasty surgery,
• Presence of neurodegenerative or neuromuscular disease,
• Psychological disorders,
• Presence of depression

The research will be carried out in Aydın ARSLAN Orthopedics and Traumatology Clinic, which is connected to the province of Istanbul, in individuals aged 40 and over who are diagnosed with knee osteoarthritis.