although lbp has generally been believed to be uncommon before the age of 20 , the prevalence of lbp among school children and adolescents has been reported to be high in different parts of the world , mostly in western countries , where it varies from 1040% . the nhanes ii ( national health and nutrition examination survey series ) reported the onset of lbp before the age of 20 in 11% of the general population . lbp prevalence rates were found to be 2831% in 2 studies carried out on school children in kuwait and tunisia . these studies show that the prevalence of lbp in children is high , equaling that of adults by the end of the growth period . lbp has a significant economic impact on individuals , society , and quality of life . many studies have analyzed the risk factors associated with lbp in children and adolescents to describe risk factors profiles [ 3,58 ] . to our knowledge there have been no reports on nlbp and related factors among school children in turkey . the aim of this study was to investigate possible factors associated with pain intensity among turkish school children with nlbp , aged 1018 years , and to determine the relationship between related factors and pain intensity using the regression tree method . this study was conducted on school children aged 1018 years in the city of denizli , located in the western part of turkey . out of 88 primary and high schools in the city , fifth and eleventh grade classes were selected from each of 10 schools ( 8 governmental and 2 private ) , using a simple random sampling method . the city department of education gave written permission , and all parents of students gave informed consent . the exclusion criteria were having any kind of musculoskeletal , rheumatic , orthopedic , somatic or psychiatric disorders . all of the exclusion criteria were considered to define nlbp more clearly because we studied nonspecific low back pain . in the sampled schools , 624 children were interviewed in total and 292 ( 46.8% ) were reported as having nlbp . after excluding the students who displayed the aforementioned disorders , 222 students ( 116 girls and 106 boys ) the visual analog scale ( vas )   was used for measuring the intensity of pain . the vas is designed to present to the respondent a rating scale with minimum constraints . this scale , shown below , was reported as the number of cm . from left of line , with range 010 : the interviewers used in the study were selected from the final year students in the physical therapy school of pamukkale university . the dependent variable was pain intensity measured in cm , and the independent variables were  bmi  ,  sex  ,  regular exercise habit  ,  studying posture  ,  transportation to / from school  ,  duration of studying  ,  bag handling  and  type of bed the participants were asked to select 1 of the following studying postures : ( 1 ) sitting on chair and studying on a table , ( 2 ) sitting on ground without chair and table , and ( 3 ) lying in prone or supine position on a bed . two methods of enquiry about nlbp were used , namely  a direct question  and  a pre - shaded manikin question  :  have you ever had low back pain ? ( look at the drawing )   have you experienced pain in the shaded area which lasted for 1 week , a month , or longer ?  students who answered both of the questions as the regression tree method ( rtm ) was used to determine risk factors that may affect pain intensity . rtm is a tree - based model , and is more useful than traditional statistical methods when a data set is large and when there are many variables . moreover , the rtm takes into consideration interactions among variables , and is not affected by high correlations between risk factors . there is no assumption about distribution shapes of risk factors , but outcome variable should be numeric . in rtm the association between risk factors ( x ) and outcome variable ( y ) ( pain intensity , in this study ) are examined by a schematic representation . homogeneous groups are constituted according to the adequate cut - off values of the risk factors . at the beginning , all individuals are collected in 1 group called a  root node  . homogeneous groups that come into being based on recursive binary splitting are termed  terminal node  . the homogeneous group means that this group is sufficiently homogeneous and can not be split any more . splitting continues until the tree reaches maximum size , and then passing the selection of adequate tree structure stage , called  pruning  . the maximum tree is not used for every data set because of its overfit structure . after pruning , the values that take place in the terminal nodes give the mean and variance of that group . two methods of enquiry about nlbp were used , namely  a direct question  and  a pre - shaded manikin question  :  have you ever had low back pain ? ( look at the drawing )   have you experienced pain in the shaded area which lasted for 1 week , a month , or longer ?  students who answered both of the questions as the regression tree method ( rtm ) was used to determine risk factors that may affect pain intensity . rtm is a tree - based model , and is more useful than traditional statistical methods when a data set is large and when there are many variables . moreover , the rtm takes into consideration interactions among variables , and is not affected by high correlations between risk factors . there is no assumption about distribution shapes of risk factors , but outcome variable should be numeric . in rtm the association between risk factors ( x ) and outcome variable ( y ) ( pain intensity , in this study ) are examined by a schematic representation . homogeneous groups are constituted according to the adequate cut - off values of the risk factors . at the beginning , all individuals are collected in 1 group called a  root node  . homogeneous groups that come into being based on recursive binary splitting are termed  terminal node  . the homogeneous group means that this group is sufficiently homogeneous and can not be split any more . splitting continues until the tree reaches maximum size , and then passing the selection of adequate tree structure stage , called  pruning  . the maximum tree is not used for every data set because of its overfit structure . after pruning , the values that take place in the terminal nodes give the mean and variance of that group . the descriptive statistics are shown ( table 1 ) as mean sd and as frequencies and percentages . the overall mean and standard deviation of pain intensity was 2.580.86 ( minimum=1 , maximum=5 ) . among the risk factors used in this study , duration of studying , type of bed , transportation to / from school , and bmi score were found to have a significant effect on pain intensity , while sex , studying posture , regular exercise habit , and bag handling were not significant ( figure 1 ) . as will be seen from figure 1 , 6 homogeneous groups are defined by the rtm according to pain intensity , with an increasing order . these are as follows : group ( id=124 ) : studies less than 4 hours , uses school bus for transportation and has 17.13 < bmi < 20.9 ( mean pain score=1.74 ) . this group is the lowest risk group among all 6 groups , giving the lowest mean . group ( id=4 ) : studies more than 4 hours and sleeps on orthopedic bed ( mean pain score=2.48 ) . group ( id=44 ) : studies less than 4 hours and uses public transportation or walks to / from school ( mean pain score=2.60 ) . group ( id=125 ) : studies less than 4 hours , uses school buses for transportation and has bmi > 20.9 ( mean pain score=2.70 ) group ( id=120 ) : studies less than 4 hours , uses school buses for transportation and has bmi < 17.13 ( mean pain score=2.86 ) . group ( id=5 ) : studies more than 4 hours and sleeps on wool or cotton beds ( mean pain score=3.11 ) . this group is the highest risk group among the 6 groups , giving the highest mean . it has become clear that a high prevalence of lbp occurs not only in adults , but also in children / adolescents . more recently , cross - sectional and longitudinal studies have focused on nlbp in children . the prevalence has been reported to vary from 10% to 40% in the literature , but the authors found it to be 46.7% in their previous cross - sectional study of 624 school children / adolescents 1018 years old . among the 8 risk factors included in the study , these factors are as follows : transportation to / from school : prista et al found that school children walking > 30 min per day to and from school are associated with an increased risk factor of lbp . they also showed that long distance walking to / from the school might lead to muscle fatigue resulting in back pain . in our study , the transportation to / from school had an important effect on lbp . bmi : the bmi score was also a significant risk factor affecting pain intensity in our study . as is well known , increased bmi score increases pain intensity in subjects with low back pain . type of bed : jacobson et al . in 2002   reported that an experimental bedding system ( ameri - spring ) reduced back pain and improved the quality of sleep . in our study we found also a significant relationship between the type of bed and low back pain intensity . this shows that quality of sleep is a very important factor affecting pain intensity for subjects who suffer from low back pain . duration of studying : we also found a significant relationship between duration of studying and nlbp intensity . korovessis et al . in 2004   reported that dorsal pain increased with increasing backpack weight among children . lee and chiou found that  poor sitting habit  were statistically associated with lbp . in our study , studying posture was not found to be an important factor . we also found that the sex of the children was not an important factor in nlbp intensity . results from the literature , as well as our study , show that taking parents and teachers concerns seriously is of vital importance . therefore , health care providers should evaluate school children carefully and make accurate observations in terms of risk factors , including duration of studying , type of bed , transportation to / from school , and obesity , to predict any severe musculoskeletal problems , especially nlbp . finally , physical factors and musculoskeletal risk factors are especially important in terms of nlbp in school children . further studies are needed to investigate psychosocial risk factors and their relationships with nlbp in school children .
summarybackgroundlow back pain ( lbp ) is a common disease among people under the age of 20 . to the best of our knowledge few studies have been carried out on lbp among school children in turkey , and none of them studied the correlation between pain intensity and related variables with lbp.material/methodsthis cross - sectional study was carried out to investigate the risk factors and their correlations with pain intensity among 222 school children ( 106 girls and 116 boys ) aged 1018 years in the city of denizli . 
 a self - reported questionnaire was used to collect the data . the regression tree method ( rtm ) 
 was used to determine the risk factors by using the statistica program package . 
 pain intensity was the outcome variable , and 8 independent variables ( body mass index ( bmi ) , sex , regular exercise habit , studying posture , transportation to / from school , duration of studying , bag handling , and type of bed ) were used to detect their effect on pain intensity.resultsthe results showed that pain intensity is significantly affected by 4 independent variables : duration of studying , type of bed , transportation to / from school , and bmi . the overall mean and standard deviation of pain intensity was 2.580.86 ( minimum=1 , maximum=5).conclusionsresults from the literature , as well as our study , show that taking parents and teachers concerns seriously is of vital importance . 
 our results indicate that parents and teachers should be informed about duration of studying , type of bed , transportation and obesity as risk factors predicting nlbp in school children .