Evaluating the suitability of prediction equations for lung function in Indian children: a practical approach.

OBJECTIVE Although several prediction equations to evaluate peak expiratory flow rate (PEFR) of Indian children are available in literature, clinicians and researchers need to make a logical choice of which equation to use as reference. The aim was to demonstrate a practical approach to making such a logical choice by using prediction equations on our study population. METHODS Eighteen linear regression equations generated on Indian children were chosen from available literature. PEFR measured on a Wright peak flow meter on 81 boys and 60 girls, aged between 8 and 13 years, was compared with the predicted values obtained from the equations. Data was systematically analyzed for the extent of over-estimation and under-estimation, correlation between the predicted and measured values and bias and limits of agreement using Bland-Altman plots. RESULTS The correlation between observed and predicted values using the eighteen equations ranged between 0.616 and 0.797 (for all P < 0.001). The Bland-Altman plots indicated that for all but three equations in boys and three equations in girls, lower measured values of PEFR were associated with higher predicted values. A final choice of a reference prediction equation was based on a combination of factors which included a high correlation between actual and predicted PEFR values, the bias of the estimate, the limits of agreement and the extent to which equations over or under-estimated PEFR. CONCLUSION A practical approach to evaluate the applicability of prediction equations on an independent data set has been demonstrated.