Cancer is one of the major causes of death in pediatric population. In Hong Kong, childhood cancer remains a significant concern in healthcare system because of its damaging impacts on adolescent's physical and psychological functions throughout their lifespan. Particularly, adolescents surviving cancer still have to bear the health burden of numerous sequelae, even their treatment is completed for months and even years.

One of the most prevalent symptoms reported by patients surviving cancer is sleep disturbance. The causes of sleep disturbance are multifactorial. However, it can largely be attributed to disruption of circadian rhythm by prolonged use of medications and long-term hospitalization. Experiencing sleep disturbance can be devastating for survivors of cancer and precipitates inflammation and oxidative stress, which are known to be a contributing factor of neurocognitive impairment. Sleep disturbance can also lead to fatigue, which in turn limits patients' capacity in engaging in daily activities and even results in depression, severely compromising patients' quality of life in the long run. Having a reliable and valid instrument that can precisely assess the problem of sleep disturbance of cancer survivors is therefore crucial for the development and evaluation of the intervention.

The Pittsburgh Sleep Quality Index (PSQI) is the most commonly and frequently used instrument to assess sleep disturbance. Because of differences in culture and language, some concepts or items in the English version may be inappropriate for adolescents living in Hong Kong. Moreover, the psychometrics of the PSQI has only been established in adolescents undergoing active treatment for cancer, when they experienced the most severe problem. It is therefore unclear whether the PSQI can also be used to assess sleep disturbance of adolescents who have completed cancer treatment. This lack of validated instruments precludes us from understanding the severity of the problem. Also, it hinders the development of appropriate interventions that promote sleep quality. This study aims to bridge the gap in existing literature by translating the PSQI from English into Chinese, and examining the psychometrics of the translated PSQI in Hong Kong Chinese childhood cancer survivors.

Cancer is one of the major causes of death in pediatric population. In Hong Kong, 46 patients aged 0 - 19 died from cancer in 2016. Childhood cancer is not common. According to Hong Kong Cancer Registry, there are approximately 190 newly diagnosed cases of childhood cancer each year. Despite this figure is not as high as that in adults, childhood cancer remains a significant concern in healthcare system because of its damaging impacts on children's physical and psychological functions throughout their lifespan. Particularly, children surviving cancer still have to pay a high price for numerous sequelae, notwithstanding their treatment is completed after months and even years.

One of the most prevalent symptoms reported by patients surviving cancer is sleep disturbance. A systematic review indicates 25 - 59 % adults reporting sleep disturbance after their treatment for cancer. A retrospective cohort study in the West also pointed out that 16.7% of childhood cancer survivors complained of disrupted sleep. The causes of sleep disturbance are multifactorial. However, it can largely be attributed to disruption of circadian rhythm by prolonged use of medications and longterm hospitalization. In fact, experiencing sleep disturbance can be devastating for survivors of cancer. Previous literature indicates that sleep disturbance precipitates inflammation and oxidative stress, which are known to be a contributing factor of neurocognitive impairment. Sleep disturbance can also lead to fatigue, which in turn limits patients' capacity in engaging in daily activities and even results in depression, severely compromising patients' quality of life in the long run. In this regard, healthcare professionals, particularly oncology nurses should bear unshrinkable responsibility to intervene this symptom with appropriate interventions, with an aim of improving the survivors' sleep quality and quality of life. Having a reliable and valid instrument that can precisely assess the problem of sleep disturbance of cancer survivors is therefore crucial for the development and evaluation of the intervention.

The Pittsburgh Sleep Quality Index (PSQI) is the most commonly used instrument to assess sleep disturbance. Although this instrument was originally developed to collect subjective information about sleep habits of psychiatric patients, it has been translated into different languages, and has been extensively applied in studies on adult cancer survivors. The results of these studies generally support this instrument to be reliable and valid in assessing sleep disturbance for this group of population. Despite the growing popularity of using this instrument in adults, no studies has so far been conducted to validate the PSQI in the pediatric population, thus limiting its usefulness for children and adolescents. In fact, a comprehensive review of the literature indicated that no validated instrument is currently available for assessing sleep disturbance of childhood cancer survivors, especially in the Hong Kong Chinese context. This lack of validated instruments precludes us from understanding the severity of the problem. Also, it hinders the development of appropriate interventions that promote sleep quality.

Inclusion Criteria:

• Hong Kong Chinese childhood cancer survivors who have completed cancer treatment for at least six months.
• Be aged 9 - 17 years.
• Be able to communicate in Cantonese and read Chinese.

Exclusion Criteria:

• Survivors with identified cognitive or behavioral problem(s) in their medical records

To assess the known-group validity, 50 pediatric cancer patients and 50 healthy children will be recruited in a pediatric oncology ward and a community center, respectively. The inclusion and exclusion for the pediatric cancer patients and healthy children will be the same as those for the childhood cancer survivors.