Presenting information on growth distance and conditional velocity in one chart: practical issues of chart design.

Growth charts, which conventionally record only cross-sectional (distance) information, can be extended to monitor growth rate over time (velocity). To adjust for regression to the mean the velocity should be conditional on the previous measurement. By working on the SDS scale rather than the measurement scale, the only extra information required for velocity is the correlation structure of the SDS at different ages. The design and validation of such combined charts is an important part of their development.