Comparison of devices used to measure blood pressure, grip strength and lung function: A randomised cross-over study.

Background: Blood pressure, grip strength and lung function are frequently assessed in longitudinal population studies, but the measurement devices used differ between studies and within studies over time. We aimed to compare measurements ascertained from different commonly used devices.

Methods: We used a randomised cross-over study.

A comparison of response rates in the English Longitudinal Study of Ageing and the Health and Retirement Study.

Survey response rates are an important measure of the quality of a survey; this is true for both longitudinal and cross-sectional surveys. However, the concept of a response rate in the context of a panel survey is more complex than is the case for a cross-sectional survey. There are typically many different response rates that can be calculated for a panel survey, each of which may be relevant for a specific purpose.