Ideally, evidence-based clinical practice guidelines relevant to your presentation will already exist. However, when that is not the case the presenter needs to seek out scientific evidence. Two primary types of evidence might be useful: systematic reviews and individual studies. ASHA CE offers a resource for finding systematic reviews and individuals studies.
Systematic reviews form the basis for evidence-based clinical practice guidelines. They are formal assessments of the body of scientific evidence related to a clinical question, and describe the extent to which various diagnostic or treatment approaches are supported by the evidence, but stop short of making specific recommendations for clinical practice.
When clinical practice guidelines or systematic reviews are not available, not current, not trustworthy, and/or not relevant, one can turn to individual studies to seek evidence to help make treatment decisions. The first place to find individual studies would be an online bibliographic database.
Unfortunately, publication in a peer-reviewed journal is not a guarantee of scientific quality. It is also important to keep in mind that studies published in English language, and particularly American journals, are less likely to include studies with negative findings than are European and other non-English journals. In order to get a comprehensive view of the evidence, both positive and negative, searching a European database such as CINAHL is valuable. Although CINAHL is more likely than MEDLINE to contain studies with negative findings, it is still more likely to publish a study with a positive than a negative finding. To find studies with negative findings, and indeed some with positive findings, one can look to the "gray" literature. The gray literature is the term given to the body of research that is not published in peer-reviewed literature. This can take the form of technical reports, conference proceedings, testimony and other unpublished evidence. Finding the gray literature is a difficult task and is typically done through conversations with content experts, relevant professional groups/organizations, and internet search engines.