Details extracted included the country, main study method, patient characteristics, intervention used to improve response, number of participants randomised to the intervention and control groups and response rate in terms of number and percentage of questionnaires returned and procedures for follow-up.
The adapted criteria covered three main issues: reporting of study methods, reporting of study findings, and interpretation of study findings (Table 1).> Electronic copies of the 10 studies were directly imported into NVivo 10 (QSR International, Melbourne, Australia), a qualitative data storage and retrieval program.
In the former case, validity can be confirmed before resources are committed to the main study; otherwise, the latter method conserves resources by not requiring additional participants.
Patients and methods In the main study, 202 relatives were followed up three times over 9 months.
It was piloted with 22 GPs using the same methods as the main study.
The patients and methods from the main study were described previously.
A paper detailing the instrument development, sample size, sampling strategy, recruitment and data collection method of the main study has been published elsewhere [ 10].
If substantial evidence of non-normality is found, appropriate alternative (non-parametric) tests will be applied, and specified as the primary analysis method in the main study.
Rosner's method requires a main study/ validation study design, in which outcome and continuous surrogate exposure measurements are obtained in n1 main study participants, and true and surrogate exposures are measured in n2 validation study participants.
Main studies detailing the method argue that rigor can be maintained with a response rate of 70% which we have reached [ 8, 10].
