... ratio of myopia 17.42% and desire to reduce to 7.5% with α = 0.05, β = 0.2 The sample size for each group are 173 students Due to the intervention study is conducted in years, to ensure that studied ... Occupational Health and Sanitation, Hanoi, pp 279-286 Vu Quang Dung, Do Van Ham, Mai Quoc Tung, Vu Thi Kim Lien, Dang Thi Tam, Nguyen Manh Hung (2008), "Initial studying on myopia in junior students ... Occupational Health and Sanitation, Hanoi, pp 287-296 Vu Quang Dung, Do Van Ham, Mai Quoc Tung, Vu Thi Kim Lien, Do Thi Yen, Nguyen Manh Hung (2008), "Studying the status of school sanitation in...