The study comprised the following components : I- Sociodemographic variables.
ii - Nutritional assessment : a - Dietary consumption:
- Dietary pattern study. - 24 hours dietary recall.
b- Anthropometric measurements :
c- Micronutrients and trace elements assessment, d- Blood count.
iii- Physical activity assessment : a- 7 days activity recall.
b- Heart rate monitoring iv- Physical fitness assessment :
a - Step Test.
b - 20 Metre Schuttle Run Test.
V - Risk variables :
a- Hypertension, b- Hyperlipidemia. c- Obesity.
d- Positive family history, e- Hypoactivity.
4.4 SAMPLE DESIGN : 4.4.1 - Target Population :
The target population of the present study were the children attending primary schools in Riyadh city during the academic year (1993 - 1994). The study comprised four groups :
Boys aged between 8.5 - 9.5 years. Boys aged between 11.5 -12.5 years. Girls aged between 8.5 - 9.5 years. Girls aged between 11.5-12.5 years The data of our target population could be summarized as follow: For Female Pupils :
ITEMS TOTAL SAMPLE NO. OF SCHOOLS 325 15 NO. OF ELIGIBLE PUPILS 36587 751 8.5 - 9.5 YEARS 20192 415 11.5- 12.5 YEARS 16395 336 ^upils :
ITEMS TOTAL SAMPLE NO. OF SCHOOLS 334 15 NO. OF ELIGIBLE PUPILS 38146 834 8.5 - 9.5 YEARS 20899 495 11.5-12.5 YEARS 17247 339
4.4.2. - Sampling frame and technique :
In order to get access to a representative sample design, the researcher developed a hierarchy for the sample frame which provided the mean access to sample selection. The present study was based on the multistage random sample technique as illustrated in the following flow chart (Figure. 1).
This method paid adequate attention to certain problems which may arise such as overcoverage and duplication.
4.4.3 - Sample size :
The determination o f sample size in the present study was approximately equal to 2% of the total number of the studied population (1585 male and female students). This coincided with our statistical estimation for sample size determina tion, which based on estimating a population proportion with specified absolute precision, as it is suitable for the proposed study and its objectives. The following equation was used to determine the minimum sample size required :
2 2
n = Z ,.cc/2P ( l - p ) / d
(n)Represents the minimum sample size required.
(Zi- oc)Represents the number of standard error from the mean.
(P)Represents the anticipated population proportion. If it is not possible to estimate p, a figure o f 0.50 could be used.
(d)Represents the absolute precision required on either site o f the proportion in percentage points (5 percentage points). (Iwanga and lemeshow, 1991)
The anticipated population proportion (p) that was used to calculate the study sample was the prevalence of anaemia among Saudi school girls aged 6-13 years which was found by Rasheed et al, (1989) in the Al-Khobar region to be
26.4% . I did not used the prevalence of anaemia among adolescent Saudi girls at Riyadh city which I found it to be 21.2% among those aged 10-11 years (Al- Shehri, 1990), for two reasons . Firstly the younger age group (8.5-9.5 years) were not included in that study . Secondly it is advisable too start the computation with the value closer to 50% (i.e. 26.4%) because, for a given precision the closer one gets to 50%, the larger the sample size that will be required (WHO, 1983).
The prevalence of anaemia was used because no reliable data was available about the prevalence of the other variables that included in this study (e.g cholesterol, blood pressure ...etc) for the age groups concerned.
F ig(l) : SAMPLING PROCEDURE FLOW CHART
Target population
4th & 6th grades of prim ary school pupils in Riyadh _________ No = (74733)_________
I
2% approximately random sample of The pupils (1585) Taken from 5% random school sample (30) Present in Different educational Authorities
I
Substratification by age and sex
Proportional Allocation^o determ ine the strata S.5-9.5 years boys (495) & girls (415) 11.5-12.5 years boys^339) & girls (336) Systematic random sampling technique to reach to the final ^urvev unitsfpupils
• For all children interview, anthropom etry, 7days activity recall, blood count &lipid profile.
• For every second Child dietary interview, micronutrients, trace elements and vitamins assessment.
• For every second boy aged 11.5-12.5 years 20-MST test. • F or every 4th child (boys & Girls) step test.
• For every 10th child (all ages) 24 hours dietary recall interview. • F or every 10th child aged 11.5-12.5 years h eart rate monitoring.
The sample size needed was calculated to be 380 pupils for each strata o f age and sex according to the proportion o f anaemia. The sample size was increased by approximately 20% to minimize the effect of non-participation or withdrawal of some students during implementation (total children invited to participate in the study was 1966 and those participated was 1585).
Randomization process:
I have used the most feasible method for this project, the multistage random sampling procedure as follows;
Riyadh city was divided into five districts according to the five Local Education Authority Offices in the city as the first stage. Then the number o f students in the sample was proportionally allocated to these five districts. The second stage was to chose 5% sample of the schools from each district using computer random numbers. Then the number of students to be selected from each school was proportionally allocated to the schools according to their total number of students in the chosen school. The third stage was to chose the individual students from the school lists according to their birth dates for the different age and sex group, starting with a random number.
4.5 - PROCEDURES OF VARIABLES ASSESSMENTS :