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Types of Research & Levels of Evidence - Introduction
The types of research you will encounter when searching for evidence-based practice information resources will include qualitative and quantitative research. Keep in mind that research studies do not have to be exclusively one or the other, many studies will use a combination of both these types of research.
The evidence you find can be ranked in a hierarchy of rigour, and is primarily divided into primary and secondary evidence.
Qualitative research is used to explore and understand people's beliefs, experiences, attitudes, behaviour and interactions. It generates descriptive, non-numerical data. Qualitative research methods include:
Documents - the study of documentary accounts of events, such as minutes of meetings
Passive observation - the systematic watching and recording of behaviour
Participant observation – here, the researcher also occupies a role or part in the setting, in addition to observing
In-depth interview - a face-to-face conversation to explore issues or topics in detail
Focus group - method of group interview which explicitly includes and uses the group interaction to generate data.
Levels of Evidence - Secondary and Primary
There are two broad types of evidence: secondary and primary. Note that we list secondary first because in Evidence-Based Practice it is the higher level of evidence and will probably be what you seek first in answering a clinical or research question.
Secondary Evidence (filtered) - is assimilated, or put together, from a number of quality primary studies on a topic. It includes systematic reviews, meta-analyses, and evidence summaries. This is sometimes referred to as filtered or pre-appraised evidence. You can find it in specialised EBP sources such as UpToDate,The Cochrane Library (notably in the Cochrane Database of Systematic Reviews) andJBI COnNECT+, and in health and medical databases such MEDLINE, PubMed and CINAHL Plus with Full Text.
Primary Evidence (unfiltered) - consists of original individual studies such as controlled trials, cohort studies, and case studies. This is sometimes referred to as unfiltered evidence. You can find primary studies in specialised EBP resources such as The Cochrane Library, notably in the Central Register of Controlled Trials, and in health and medical databases. You can search for primary research in journal databases such as CINAHL Plus with Full Text and Medline.
Quantitative research is used to generate numerical data or data that can be converted into numbers. Study types that are used in the health and medical field include:
Case report or case series - a report on one or more individual patients. There is no "control group" so this study type is considered to have low statistical validity
Case control study - this studies patients with a particular outcome (cases) and control patients without the outcome. Is useful in aetiology (causation) research but prone to causation error
Cohort study – identifies and follows two groups (cohorts) of patients, one having received the intervention being studied, and and one having not. Useful in both aetiology and prognosis research. Because the groups are not randomised, they may differ in ways other than in the variable under study
Randomised Controlled Trial (RCT) - a clinical trial in which participants are randomly allocated to a test treatment and a control. This is considered the “gold standard” in testing the efficacy of an intervention. RCTs include methodologies - randomisation and blinding - that reduce the potential for bias and provide good evidence for cause and effect.