Table 3. Test-retest study: Intra class correlation coefficients between two estimations of total energy expenditure measured at two different times, 6 weeks apart, over one year period in the random sample of 121 young students from Bogotá, 2001-2002. Categories N Intra-class correlation coefficient [95% CI] All 121 .96 [.95 ; .97] Age (years) 8-10 41 .94 [.89 ; .97] 11-13 40 .98 [.96 ; .99] 14-16 40 .95 [.91 ; .98] Gender Male 56 .98 [.96 ; .99] Female 65 .95 [.91 ; .97] School grade Elementary School 41 .98 [.97 ; .99] Secondary School 80 .94 [.91 ; .96] Period activities Vacation period 121 .97 [.96 ; .98] School period 121 .96 [.94 ; .97] Socio-economic strata (see map) 1-2 46 .94 [.90 ; .97] 3-4 40 .98 [.96 ; .99] 5-6 35 .99[.97 ; .99] Activities 1- Sleeping 121 .93[.91 ; .95] 2- Toilet 121 .90[.87 ; .93] 3- Meals 121 .97[.96 ; .98] 4- Transportation 121 .84[.78 ; .89] 5- Classroom 121 .97[.96 ; .98] 6- Mandatory physical education 121 .95[.93 ; .97] 7- Other activities in school 121 .94[.92 ; .96] 8- Out school activities 121 .96[.94 ; 97] 9- Religious activities 121 .93[.90 ; .95] 10- Vacations 121 .97[.96 ; .98] 11- Personal artistic activities 121 .98[.97 ; .99] 12- Sport competition 121 .98[.97 ; .99] 13- Home activities 121 .89[.85 ; .92]