The evidence, once gathered, needs to be interpreted (see box). Since conclusive evidence exists for relatively few healthcare procedures, deriving recommendations solely in areas of strong evidence would lead to a guideline of limited scope or applicability.17
This could be sufficient if, for example, the guideline is to recommend the most strongly supported treatments for a given illness, but more commonly the evidence needs to be interpreted into a clinical, public health, policy, or payment context. Therefore within the guideline development process a decision should be taken about how opinion will be both used and gathered.
Factors contributing to the process of deriving recommendations
- The nature of the evidence (for example, its susceptibility to bias)
- The applicability of the evidence to the population of interest (its generalisability)
- Knowledge of the healthcare system
- Beliefs and values of the panel
Using and gathering opinion
Opinion will be used to interpret evidence and also to derive recommendations in the absence of evidence. When evidence is being interpreted, opinion is needed to assess issues such as the generalisability of evidence—for example, to what degree evidence from small randomised clinical trials or controlled observational studies may be generalised, or to extrapolate results from a study in one population to the population of interest in the guideline (extrapolating a study in a tertiary, academic medical centre to the community population of interest to potential users of the guideline).
Recommendations based solely on clinical judgment and experience are likely to be more susceptible to bias and self interest. Therefore, after deciding what role expert opinion is to play, the next step is deciding how to collect and assess expert opinion. There is currently no optimal method for this, but the process needs to be made as explicit as possible.
Resource implications and feasibility
In addition to scientific evidence and the opinions of expert clinicians, practice guidelines must often take account of the resource implications and feasibility of interventions. Judgments about whether the costs of tests or treatments are reasonable depend on how cost effectiveness is defined and calculated, on the perspective taken (for example, clinicians often view cost implications differently than would payers or society at large), and on the resource constraints of the healthcare system (for example, cash limited public systems versus private insurance based systems). Feasibility issues worth considering include the time, skills, staff, and equipment necessary for the provider to carry out the recommendations, and the ability of patients and systems of care to implement them.
It is common to grade each recommendation in the guideline. Such information provides the user with an indication of the guideline development group’s confidence that following the guideline will produce the desired health outcome. “Strength of recommendation” classification schemes (such as the one in the box) range from simple to complex; no one scheme has been shown to be superior. Given the factors that contribute to a recommendation, strong evidence does not always produce a strong recommendation, and the classification should allow for this. The classification is probably best done by the group panel, using a democratic voting process after group discussion of the strength of the evidence.