1. RELIABILITY AND VALIDITY AT ALL STAGES
Design and methodology;
Sampling;
Instrumentation;
Timing;
Data collection;
Data analysis;
Data reporting.

2. IMPROVING RELIABILITY
Minimise external sources of variation;
Standardise conditions under which measurement occurs;
Improve researcher consistency;
Broaden the sample of measurement questions by:
adding similar questions to the instrument;
increasing the number of researchers (triangulation);
increasing the number of occasions in an observational study.
Exclude extreme responses (outliers).