Optimal design for longitudinal studies to estimate pubertal height growth in individuals.

BACKGROUND: The SITAR model expresses individual pubertal height growth in terms of mean size, peak height velocity (PHV) and age at PHV. AIM: To use SITAR to identify the optimal time interval between measurements to summarise individual pubertal height growth. SUBJECTS AND METHODS: Heights in 3172 boys aged 9-19 years from Christ's Hospital School measured on 128 679 occasions (a median of 42 heights per boy) were analysed using the SITAR (SuperImposition by Translation And Rotation) mixed effects growth curve model, which estimates a mean curve and three subject-specific random effects. Separate models were fitted to sub-sets of the data with measurement intervals of 2, 3, 4, 6, 12 and 24 months, and the different models were compared. RESULTS: The models for intervals 2-12 months gave effectively identical results for the residual standard deviation (0.8 cm), mean spline curve (6 degrees of freedom) and random effects (correlations >0.9), showing there is no benefit in measuring height more often than annually. The model for 2-year intervals fitted slightly less well, but needed just four-to-five measurements per individual. CONCLUSIONS: Height during puberty needs to be measured only annually and, with slightly lower precision, just four biennial measurements can be sufficient.

Randomised crossover trial of rate feedback and force during chest compressions for paediatric cardiopulmonary resuscitation.

OBJECTIVE: To determine the effect of visual feedback on rate of chest compressions, secondarily relating the forces used. DESIGN: Randomised crossover trial. SETTING: Tertiary teaching hospital. SUBJECTS: Fifty trained hospital staff. INTERVENTIONS: A thin sensor-mat placed over the manikin's chest measured rate and force. Rescuers applied compressions to the same paediatric manikin for two sessions. During one session they received visual feedback comparing their real-time rate with published guidelines. OUTCOME MEASURES: Primary: compression rate. Secondary: compression and residual forces. RESULTS: Rate of chest compressions (compressions per minute (compressions per minute; cpm)) varied widely (mean (SD) 111 (13), range 89-168), with a fourfold difference in variation during session 1 between those receiving and not receiving feedback (108 (5) vs 120 (20)). The interaction of session by feedback order was highly significant, indicating that this difference in mean rate between sessions was 14 cpm less (95% CI -22 to -5, p=0.002) in those given feedback first compared with those given it second. Compression force (N) varied widely (mean (SD) 306 (94); range 142-769). Those receiving feedback second (as opposed to first) used significantly lower force (adjusted mean difference -80 (95% CI -128 to -32), p=0.002). Mean residual force (18 N, SD 12, range 0-49) was unaffected by the intervention. CONCLUSIONS: While visual feedback restricted excessive compression rates to within the prescribed range, applied force remained widely variable. The forces required may differ with growth, but such variation treating one manikin is alarming. Feedback technologies additionally measuring force (effort) could help to standardise and define effective treatments throughout childhood.