Nursing Library Resources: Types of Studies & Study Design Terminology for EBP

Cohort Studies

• Cohort studies observe groups of individuals before they develop a disease or a particular outcome.
• They do so by comparing two groups, such as the subjects with exposure/risk factor to the subjects without exposure/risk factor, for differences in incidence of outcome/disease.
• Cohort studies have the power to detect many different outcomes of an exposure and allow researchers to calculate a relative risk of developing a disease based on different exposures.
• Prospective cohort studies follow subjects from presence of risk factors/exposure to development of disease/outcome.
• retrospective cohort studies identify a population with and without the risk factor/exposure based on past records and then assess if they had developed the disease/outcome at the time of study. 

Case-Control Studies

• case-control studies begin with the outcomes and do not follow people over time.
• Case‐control studies are study designs that compare two groups, such as the subjects with disease (cases) to the subjects without disease (controls), and to look for differences in risk factors. 
• researchers choose people with a particular result (the cases) and interview the groups or check their records to ascertain what different experiences they had. 
• Can suggest a casual relationship relationship but cannot prove a hypothesis. 

Case Reports and Case Series

• Clinical presentation on a case that is atypical or out of the norm. 
• Provides a detailed and comprehensive description of the case. 
• Cannot be generalized to a larger population.
• A series of individual case reports makes a case series.

Surveys

• Surveys gather data to describe the demographics of a group; the health status of a group of people at a particular time; the utilization of medical services; or the knowledge, beliefs, and attitudes of people regarding health practices.
• Surveys are a major data collection method in health services research.
• Survey research is extremely complex.
• Survey results often are difficult to interpret and generalize to other groups and time periods but provide wonderful insights into the practices and health conditions of large groups of people as well as clues for future investigation.

Cross-Sectional Study

• Cross-sectional studies look to evaluate an association between an exposure and outcome at the same time.
• Participants in a cross sectional study are selected based on the inclusion and exclusion criteria defined for the study.
• Once participants have been identified, the investigator follows the study to assess exposure and outcomes.
• Cross-sectional designs are typically used for population-based surveys to assess the prevalence of disease in clinic-based samples.
• Cross-sectional studies are a one time measurement, so it is difficult to derive relationships from the analysis. 

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Meta-analysis 

• Systematically reviewing data across several studies to combine pertinent qualitative and quantitative data and develop a single conclusion based on the review. 
• This type of review provides a complex analysis of harms, safety data, and benefits.
• Provides a greater ability to apply to the general population effected. 
• It can be difficult and time consuming to identify appropriate studies for review. 

Systematic Review

• A document often written by a panel that provides a comprehensive review of all relevant studies on a particular clinical or health-related topic. 
• Created after reviewing and combining all the information in both published and unpublished studies.
• Summarizes the findings of all of the included studies.
• This type of study is considered and evidence-based resource and can be applied to the general population more broadly than individual studies

Practice Guideline

• A statement produced by a group of experts that outlines current best practices to inform health care and clinical decisions.
• Produced after an extensive review of the relevant literature (i.e., studies, other reviews, etc.)
• Good guidelines clearly define the topic and summarize the best evidence regarding therapy, harm, prevention, diagnosis, prognosis, and other clinical decisions.
• They should also outline decision points where information should be integrated with patient values.
• Also referred to as "evidence-based guidelines" or "clinical guidelines."

• Abstract: A brief summary or overview of the research study.
• Causality: the relationship between the cause and effect
• Cohort: A group that shares common characteristics among it's members. 
• Confounding variables: variables that cause/prevent an outcome from occurring outside of or alongside the variable being studied. These variables make it difficult to distinguish the relationship between the variable and outcome. 
• Consent: an agreement given by a competent person to participate in a research study
• Control Group: participants from the research group who won't receive the experimental treatment or variable. Those in the control group will be compared with those receiving the treatment in order to establish its effectiveness. 
• Correlation: A relationship between two variables, but not neccesarily a causation relationship. 
• Double-Blind Study: A study conducted in which neither the investigators nor the participants know specific details of the study, such as whether a placebo is being administered. 
• Effectiveness: How well a treatment works in the real world. 
• Efficacy: How well a treatment works in the study.
• Empirical Research: The study, based on direct observation, use of statistical records, interviews, or experimental methods, of actual practices or the actual impact of practices or policies.
• Exclusion Criteria: The set of conditions that characterize some individuals which result in being excluded in the study 
• Experimental research group: participants from the research group that will receive the experimental treatment or variable. 
• Hypothesis: an educated prediction about the expected outcome of a study. 
• Inclusion Criteria: The set of conditions that studies, or patients must meet to be included in the review.
• Literature Review: A literature review is a summary and analysis of research published on a specific topic. Literature reviews give an overview of individual articles and explain how each work has contributed to the field's understanding of the topic
• Longitudinal Studies: Studies in which variables relating to an individual or group of individuals are assessed over a period of time.
• Mean: the average score between two variables or outcomes. 
• Meta-Analysis: Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.
• Outcome: the result of an intervention or of the study. 
• Population Bias/Volunteer Bias: A sample may be biased and skewed by those who participate in a study. 
• Prospective Study: A study that moves forward in time, or that the outcomes are being observed as they occur, as opposed to a retrospective study, which looks back on outcomes that have already taken place.
• Qualitative Studies: Quantitative research is research that uses numerical analysis.
• Sample Size: The number of units (persons, animals, patients, specified circumstances, etc.) in a population to be studied. The sample size should be big enough to have a high likelihood of detecting a true difference between two groups.
• Single-Blind Study: a study in which the investigators know the specifics of the study, but the participants don't. 
• Variable: An intervention or action that is being studied to observe its effect on the research group. 

For more information on Study Design Terminology, see the following resources:

Clinical Trials

• Also known as therapeutic trials
• subjects with particular disease/conditions are placed in different treatment groups
• can be used to evaluate new therapies, procedures, devices
• select a sample population that is best representative of the general population, so that it can be generalized

Randomized Clinical Trials

• RCTs follow two groups of people over time to see who achieves a particular result. In this case, the researchers assign or randomize the people to their groups.
• each person has an equal chance of being assigned to either group
• each group receives a different intervention. When the study period ends, the researchers evaluate their different outcomes and calculate the risk of one group developing the result compared to another.
• advantages include the advantage in assessing causality, and the intervention caused the results is clearly demonstrated.
• disadvantages include expense and time-consumption, and bias to the results if participants are not properly blinded.

Non-Randomized Clinical Trial

• Uses an approach to selecting controls without randomization
• The selection of subjects is predictable, and there for there is bias in regard to subjects and controls
• This type of study depends on already collected data from different sources such as medical records and published literature
• Information obtained may lack uniformity, completeness, accuracy, or reliability 

Cross-Over Clinical Trial

• In this study design each group receives different treatments during different time periods of the study, and the subjects cross over from one treatment to the next during the course of the trial
• This type of study works best with chronic illness in which there is no cure, only improvement of the condition or quality of life
• The intervention must be temporary (ex: drug treatment), and allow for a wash-out period before the next intervention round