Service evaluation is designed and conducted solely to define or assess current care.  

It addresses the question "what standard does this service achieve?"

It assesses choices of treatment, care or services that are currently available according to guidance, professional standards and/or patient/service user preference.

Examples include:

• evaluations performed to assess current care of a patient
• evaluations of the standard of care a service achieves
• evalutions aimed at deterimining or chosing appropriate treatment or service options.

Clinical audit is designed to answer the question: "does this service reach a predetermined standard?"

It measures the delivery of an intervention against a standard.  It only assesses choices of treatment, care or services that are currently available according to guidance, professional standards and/or patient/service user preference.

Examples include:

• evalutations designed to inform best service or care delivery
• evalutions of whether or not a care or service meets required standards
• evaluations relating to current treatments or interventions.

Usual practice addresses questions such as: “what are the health issues in this population and how do we address them?” or “what is the cause of this disease outbreak or incident and how do we manage it?”

Usual practice may involve systematic, quantitative or qualitative methods.  however, it assess choices of intervention, treatment, care or services based on best public health evidence or professional consensus.

It may involve analysis of existing routine data or administration of interview or questionnaire to those in the population of interest.  it may involve a review of existing evidence.

Examples include:

• investigations designed to determine the cause of an outbreak of disease
• investigations designed to assess population health issues.