Elaboración de políticas contables y estimaciones

Based on the ratio of schools in each district, a total of 13 schools made up of 6 schools (3 public and 3 private), 5 schools (3 public and 2 private), and 2 schools (1public and 1private) were selected by simple random sampling from Diobu, Township and Trans –Amadi districts respectively. Three public and 2 private schools were selected from the Township district (as it was the only district with an odd number of schools to be selected from it) even though there were 26 public and 27 private schools in that district. This would also allow for the higher proportion of total public to total private schools in Port Harcourt (1.1:1) which is almost equal to the proportion of public to private schools (7:6) chosen for this study.

Stage 2: Selection of arms of classes

In schools with more than one arm of a class, one arm was selected randomly to represent the others, while in schools with only one arm of a class, that arm was chosen. Arms were selected from all six classes in all the selected schools.

Stage 3: Selection of pupils

In each selected school an average of 100 pupils aged 6- 12 years were recruited.

Fifteen to twenty pupils were selected randomly from each class using the class register.

TRAINING AND STANDARDIZATION OF SURVEY TEAM

Ten post internship doctors were used as research assistants with 3 – 4 assisting per day. They had 4 hours of training at the Department of paediatrics, UPTH side laboratory one week prior to the field work. This training was done by the investigator. The training was on weight and height measurement. The doctors were taught on weight measurement using a quality beam balance in kilogrammes with an accuracy of 0.1kg. The doctors (subjects) were weighed standing on the scale with their shoes off. The scales were checked regularly for zero adjustment before and after each reading.

Measurement of height using a portable stadiometre, consisting of an anthropometre with a simple triangular headboard was also demonstrated. In taking the height, the subjects were made to stand straight with their shoes off and head held erect such that the external auditory meatus and the lower border of the orbit were in one horizontal plane (Frankfurt plane). The buttocks, shoulder blades, and heels touched the measurement surface with knees and legs together, and arms hanging naturally by the side. A movable triangular headboard was brought against the crown of the head and the height measurement read off at the maximum inspiration to the nearest centimetre. All measurements were taken twice and the average taken.

CONDUCT OF STUDY

The study was carried out from 1^st February to 31^st May 2010. Consent letters (Appendix 5) and pre-tested questionnaires (Appendix 6) were sent to parents of the selected subjects prior to screening. Parents that gave consent were required to fill and return the questionnaires to the school which were retrieved by the investigator at the time of screening. The interval from filling the questionnaires to screening of the pupils was an average of 4 days. The questionnaires contained biodata of the subjects, data on socioeconomic status, family medical history and ethnicity. The questionnaires were self-administered by the parents. The researcher had separate orientation sessions with the teachers and pupils to pass across information on blood pressure and how it will be measured in each school visited. This was done in order to create awareness of childhood hypertension in the teachers and attract their cooperation. It was also done to allay any anxiety of the pupils.

The subjects were screened for hypertension with measurement of blood pressure (BP), height and weight. Blood pressure was measured according to task force recommendations using the mercury gravity sphygmomanometre.¹ The measurements were taken in the sitting position with exposed outstretched right arm on a table, using appropriate cuff size for age,¹ the cuff bladder completely encircling the arm covering 75% of the arm between the acromion and olecranon and the bell of the stethoscope placed over the brachial pulse, the proximal medial part of the anti-cubital fossa. For each measurement, the cuff was rapidly inflated to occlude the brachial artery, and then deflated slowly allowing the mercury column of the sphygmomanometre to fall at a rate of approximately 2 - 5 mm Hg per second. The first Korotkoff sound was taken as systolic BP and the fifth

Korotkoff sound as the diastolic BP. Blood pressure was measured three times for each child in the same visit with at least two minutes interval between measurements. The average was then estimated as the blood pressure level of the subject.¹ Blood pressure was done by the researcher alone to avoid inter-observer error. The charts on BP levels for boys and girls by age and height percentiles³⁰ were used to classify hypertension in the subjects after determining their height percentiles from the CDC growth charts (Appendix 2). For children with a raised BP, two additional BP measurements were made at least a week apart.

Height was measured on a portable stadiometre in centimetres with an accuracy of 0.1cm. Weight was measured with a quality beam balance in kilogrammes with an accuracy of 0.1kg. The scale was zeroed daily and standardized with standard weights monthly. Weight and height were measured by assistants who were trained by the researcher prior to the study to avoid inter-observer errors. They took the average of two measurements of the weight and height to avoid intra-observer errors. Weight and height were measured with light clothes on and without shoes.

DATA ANALYSIS

Data was collated and analyzed by the investigator using the Epi-info version 3.5.1 statistical software. In this study, hypertension was defined as average of 3 measured systolic and/or diastolic BP that is greater than or equal to the 95th percentile for gender, age, and height using the standard BP charts developed by the United States of America.³⁰ The body mass index (BMI) was calculated as the weight in kilogrammes divided by the square of the height in metres. Using the BMI for age charts (Appendix 2) children with a BMI of less than the 5^th percentile were

classified as underweight, those with BMI from the 5^th to 85^th percentile as normal weight, those with BMI greater than the 85^th but less than the 95^th percentile as over weight and those with BMI equal to or greater than the 95^th percentile as obese.⁸⁴ The socio-economic status was determined by the social classification scheme developed by Oyedeji⁸⁵ (Appendix 7) which was further modified at analysis to classify the study group into upper and middle/lower socio-economic groups.

Data obtained are presented in tables, charts and graphs. Comparison of means was done using the student t test and chi square for proportions. A p value of less than 0.05 was considered as statistically significant.