Sample
Children in the Limpopo Province of South Africa, consisting of 7 ethnic groups (Northern Sotho, Venda, Tsonga, Tswana, North Ndebele, Bolobedu, and Afrikaans) were recruited from a school-based population. The 528 children (378 boys and 150 girls) were recruited following screening for ADHD of the general population of primary school children representative of all socio-economic levels. Written permission was obtained from the Department of Education, Limpopo Province, as well of the principals of the selected schools.
The Disruptive Behavior Disorders (DBD) rating scale [31,32] was standardized for the populations of the Limpopo province of South Africa in an earlier study [14] and used as the screening instrument. Participation was voluntary. Informed consent was obtained from the child's parents or guardians. Both teachers and parents were given the rating scale to complete. Only the teacher's ratings were used for the screening, since the return of the parent's rating scale was below 50%, probably because many children either did not live with their parents or the parents were illiterate. Teacher ratings are usually regarded as an accurate measure of assessment [6]. The return of the teacher's rating scale was however close to 100%. The children meeting the criteria for inclusion into the groups with ADHD symptoms (~7%) were selected for further testing. They were matched for gender, age, and ethnic group with children who did not meet the inclusion criteria, obtained from the screening process.
Children were divided into a group with symptoms of ADHD and a comparison group without ADHD symptoms (Table 1), based on teacher ratings on the DBD rating scale [31,32]. Cut off points for the group with ADHD symptoms (95th percentile or above) and comparison group (85th percentile or below) were based on the results from the prevalence study [14] in which more than 6000 children in the Limpopo Province were rated on the DBD. According to the norms, scores on hyperactive/impulsive related items less than 15 and inattentive items less than 17 were regarded as comparisons. Scores higher than 18 on the Hyperactive/Impulsive items were classified as having symptoms of ADHD-HI and higher than 21 on the Inattention items were classified as having ADHD-PI symptoms. If the criteria were met on both types of items they were classified as having symptoms of ADHD-C.
The final sample consisted of children from seven ethnic groups inhabiting the Limpopo Province (Table 1). Children with an IQ lower than 80 and/or with a history of neurological problems (e.g. epilepsy, head injuries, cerebral palsy, or cerebral malaria) were excluded. None of the children was on psychostimulant medication at the time of testing.
Instruments
Assessment of, and research, on ADHD in developing countries like South Africa could be improved with standardized tests reliably differentiating between children with and without ADHD symptoms. The tests selected in the present study measure various aspects of fine motor functions, mainly assess basic non-verbal skills. They are simple, inexpensive, easy to transport to and use in remote rural areas without the conveniences of Western settings.
The three tests which measure different aspects of fine manual motor skills were the Grooved Pegboard Test [33] (distal, complex fine motor coordination and psychomotor speed), the Maze Coordination Task [33] (tactual motor coordination skills) and the Finger Tapping Test [34] (pure motor speed).
The Grooved Pegboard apparatus (Lafayette Instrument Company, #4202) consists of a metal board (10 × 10 cm) that contains a 5 × 5 set of holes each with a groove oriented randomly in different directions. Twenty-five round metal pegs with a ridge running lengthwise have to be rotated into the correct position for insertion into the holes. The child is instructed to insert the pegs as fast as possible, completing one row before starting on the next. The test is performed once with each hand, always starting with the dominant hand. Time to completion (in s) is the final score for each hand.
The following instruction is given in the child's own language:
"You are now going to put each of these pegs into the holes of this board (show). You can only use one hand. Pick up one peg at a time. Notice that the pegs are not round, neither are the holes in the board. In order to insert it you will have to rotate the peg so that it fits exactly (show two pegs, let the child try the three next, then remove all five pegs from the holes). When I tell you to start, you shall start over here (point to the upper left hole if the child is using its right hand and to the upper right hole if the child is using its left hand), fill this upper row, continue on the next, and so on until all the pegs are inserted. Try to be quick. Use only your (dominant/non-dominant) hand."
The Maze Coordination Task (Lafayette Instrument Company, #2706A) is a simple maze without blind alleys. The maze is placed at ~60 degree angle with the table. The child is required to go through the maze with an electric stylus, trying not to touch the sides. The stylus is connected to an electronic clock and a counter, which record the number of contacts the stylus is making with the sides (counter) and the cumulative time these contacts last (timer). The aim is to move the stylus through the maze, without touching the sides. There is no speed requirement. The test is performed twice with each hand. The total sum of touches and cumulative time of contact of two trials with the same-side hand are the final scores.
The following instruction is given in the child's own language:
"In this test, take this stylus and move it through the maze all the way to here (point). Try to avoid touching the sides (show). Do this with about this speed. (Show by moving stylus through about 1/4 of the maze). You do not have to rush, if you move too quickly you will make more errors. Try to be accurate. Start with your (dominant) hand. Do not rest your hand or arm against anything".
The Finger Tapping Test apparatus (Marquardt, type 0925.0201) is a micro-switch operated by a key consisting of a metal arm and a round disk (20 mm in diameter). The key is placed at the short end of a 223 mm × 151 mm × 38 mm (h) plastic box where the operating hand is to be rested. The length of the metal arm from the micro-switch to the centre of the disc is 60 mm. The switch needs ~65 g dead weight to close. An electronic counter records the number of micro-switch closings (taps). The child has to press the switch ~15 mm to activate the counter. It is important that the hand is rested in a constant position in contact with the surface of the plastic box to ensure that only the index finger is moving. A stopwatch is used to time each 10-s trial. The child may rest at any time between trials, but is told to take a break at least after every third trial. For each hand, the test is terminated after ten trials, or when five consecutive trials do not vary by more than five taps. The means of the five trials with the highest number of taps are computed for each hand and used as the final scores.
The following instruction is given in the child's own language:
"Can you, please, show me how fast you can press this button with your (dominant) index finger? (If the child is small, touch the index finger. Demonstrate what the child has to do). Rest your arm in a comfortable position and try for yourself. You have to press the button all the way down and release it, or the counter will not work properly. Keep your wrist and arm still and remember to press as fast as you can. I will tell you when to start and when to stop."
Procedure
The children were always tested by a tester fluent in the child's own language. Most assessments of motor functions of the South African children were done at their schools during school hours. The exceptions were the children whose school was within a radius of 2 km from the University and the children referred for assessment, which were tested at the University Clinic.
To assess hand dominance, the children were asked to hit a nail with a small hammer, throw a ball, and to write their name. Experimental tests were presented in the following order: Grooved Pegboard, Maze Coordination Task, and Finger Tapping Test. For the Afrikaans group, the IQ was established with the Senior South African Individual Scale (SSAIS) [35]. As there are no standardized IQ tests for the indigenous African populations, Raven's progressive matrices was used to estimate IQ [36,37]. This test is considered to be culture-fair [38]. The actual testing procedure for each child lasted about 45 min and was conducted by intern clinical psychologists.
Statistical analysis
Raw scores were converted to standard scores (z-scores) for each ethnic group, to eliminate the effects of possible differences between testers and the translation of instructions. Group differences on demographic variables were analysed using analysis of variance (ANOVA) using the Statistica 6.1 programme [39]. The results were analysed twice with 4 × 2 × 2 (subtype × gender × hand dominance and subtype × age group × hand dominance) ANOVA's for independent samples, with dominant vs. non-dominant hand as within-child repeated measure. Post-hoc tests consisted of multiple comparisons using the Bonferroni correction.
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