It is often easier to audit structures (e.g. premises, records, workforce characteristics) and processes (e.g. practice procedures, medical interventions) than outcomes (e.g. impact of care or services). It may be many years before the impact or outcomes of care such as lengthening lifespan can be measured. There may be confounding factors that have contributed to bringing about the improvements. The outcome may be an absence of illness or harm which is impossible to identify accurately, e.g. prevention of pregnancy or a sexually transmitted infection; rather than a positive health gain.