study designs in nursing research

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Evidence Based Nursing Practice

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Levels of Evidence

As the different study designs have different strengths, and weakness, they have been ranked in levels of evidence. Simply put, the strongest designs are at the top, the weakest at the bottom. The pyramid is a convenient symbol for this, as there are usually fewer randomized trials say, than case reports.

For an interactive version, go to: https://library.muhealth.org/evidencepyramid/

Click on the image to see larger version.

Study Types/Designs

Case Report - a write up of the case of an individual patient; a clinical presentation. Often the first report of a new disease or disease trend.

Case Series - a write up of the cases of several patients all undergoing similar treatment.

Case-Control Study - a comparison of study subjects with a particular disease/risk factor (cases) to those without (controls). These have also been called retrospective studies. A good design for rare diseases but easy to get poor data.

Clinical Trial - an experimental study in which subjects receive an intervention. Preferably subjects are assigned to either treatment or no treatment/placebo (see Controlled Clinical Trial). Some trials compare multiple treatments, e.g. the subjects could be assigned to: Treatment A, Treatment B, No treatment/placebo. The different groups are called arms. This is the best study design for testing effect of interventions.

Cohort Study - a group of subjects followed through time. Cohort studies can be used to track effect of an exposure, e.g. all subjects had been exposed to lead in their housing, or they can track a cohort not exposed. They have also been called prospective studies. This is a strong design for determining risk and incidence.

Controlled Clinical Trial - a Clinical Trial where there is a control group receiving a comparison treatment or no treatment/placebo.

Cross Sectional Study - a descriptive study that documents the number of people with a particular disease or risk factor.

Randomized Controlled Trial - Same as Controlled Clinical Trial, with the added benefit of the subjects being randomly assigned to treatment/no treatment arms. This avoids selection bias as all subjects have an equal chance of being assigned to any one of the treatment/no treatment arms. Random assignment can be accomplished using machine generated random number tables. Assigning subjects using methods such as coin tosses or assigning even-odd numbers is considered pseudo-randomization.

Review articles are not considered evidence . One exception to this are Systematic Reviews - including their subset, Meta-Analysis .

Why are Systematic Reviews included in the evidence based pantheon? They aim for documented, exhaustive and comprehensive searching for all research on a specified topic. Most other types of reviews either do not document their search and collection of the research nor do they verify that they have completed an exhaustive and comprehensive search.

All things random

In evidence based practice, much is made of Randomized Control Trials (i.e. clinical trials where participants are randomized assigned to an interventions, including a control group.) Why? Randomized Control Trials - RCTs - can show cause and effect not just association.

However, they are not the only study design available. This page provides a glossary (left column) of some of them. For more info & a nifty chart, check out CEBM's Study Design site.

Making sense of it all

Study designs can be classified as descriptive or analytical . The analytical studies have more power, or ability to predict, than descriptive studies and therefore rank higher in the evidence based world.

Descriptive studies give us a snap shot of what is happening. Surveys, case reports, cross sectional studies (using surveys) are descriptive. They cannot show cause and effect, but they can show prevalence or incidence. They can also be useful in spotting trends.

Analytical studies measure the relationship between factors. Cohort studies and randomized control trials are analytical. They show cause and effect.

For more information or in depth definitions, see College of Veterinary Medicine, Washington State University.

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Research Methods in Nursing

Qualitative, quantitative, observational, correlational, quasi-experimental, experimental, mixed-methods, triangulation, ask a librarian.

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QUALitative research "is best suited for research aimed at rich description or in-depth understanding of a phenomenon, rather than determining causality; it is particularly useful in understanding the relevance of contextual features in the expression of the phenomenon. Qualitative approaches are most often chosen when little is known about a topic or when new perspectives are needed; other functions of qualitative approaches include generating hypotheses, refining theory, providing illustrative examples, creating taxonomies, and generating items for instrument development.

Relying primarily on inductive rather than deductive processes, qualitative studies generally share several “ground-up” features that differentiate them from “top-down” quantitative research. These features are driven by two central tenets: an orientation to cases rather than variables, as well as a preference for emergent rather than fixed designs."

More Information from Encyclopedia of Nursing Research

Four types of qualitative research design often applied to nursing research are:

Phenomenology - the study of human life experiences and how they appear in human consciousness
Grounded Theory - seeks to explain variations in social interactional and social structural problems and processes
Ethnography - As a research process, ethnography is a comparative method for investigating patterns of human behavior and cognition through observations and interactions in natural settings
Narrative Inquiry - the analysis of meaning in context through interpretation of persons' life experiences

For more details , look up these research designs in:

Encyclopedia of Nursing Research

Dictionary of Nursing Theory and Research

QUANtitative research "consists of the collection, tabulation, summarization, and analysis of numerical data for the purpose of answering research questions or hypotheses. The term quantitative research is of recent origin and is distinguished from qualitative research in design, process, and the use of quantification techniques to measure and analyze the data. The vast majority of all nursing studies can be classified as quantitative.

Quantitative research uses statistical methodology at every stage in the research process. At the inception of a research project, when the research questions are formulated, thought must be given to how the research variables are to be quantified, defined, measured, and analyzed. Study subjects are often selected for a research project through the statistical method of random sampling, which promotes an unbiased representation of the target population among the sample from whom generalizations will be made. Statistical methods are used to summarize study data, to determine sampling error, and in studies in which hypotheses are tested, to analyze whether results obtained exceed those that could be attributed to sampling error (chance) alone."

Quantitative Research Design can be Non-Experimental (Descriptive or Correlational) or Experimental (including Quasi-Experimental).

" Observational designs are nonexperimental, quantitative designs. In contrast to experimental designs in which the investigator manipulates the independent variable and observes its effect, the investigator conducting observational research observes both the independent and dependent variables. In observational studies, variation in the independent variable may be due to genetic endowment, self-selection, or occupational or environmental exposures."

" Correlational research examines the relationships between variables, but unlike experimental or quasi-experimental studies, correlational studies lack active manipulation of the independent variable(s). Therefore, postulation of relationships among study variables in causal terms is risky. Discussion of associations in correlational studies, however, sometimes gives an indication of how likely it is that a cause-and-effect relationship might exist."

More Information from Dictionary of Nursing Theory and Research

" Quasi-experimental research is similar to experimental research in that there is manipulation of an independent variable. It differs from experimental research because there is no control group, no random selection, no random assignment, and/or no active manipulation. Quasi-experimental research is a useful way to test causality in settings when it is impossible or unethical to randomly assign subjects to treatment and control groups or to withhold treatment from some subjects."

Experimental research "involves manipulation of the principal independent variable, i.e., the actual administration of treatments or interventions that comprise the categories of the independent variable. An investigation is made of the effect of the independent variable on the dependent variable.

A true experiment is characterized by random assignment of individual subjects to the treatment conditions and a high degree of control over unwanted influence of extraneous variables and other factors that could bias the results of the study."

"True experiments have the potential to provide strong evidence about the hypothesized causal relationship between independent and dependent variables. Experiments are characterized by manipulation, control, and randomization. The quality of experiments depends on the validity of their design."

" Mixed methods research is a term associated with research that uses a combination of methods that are usually identified with qualitative research and methods that are usually identified with quantitative research. It should not be confused with the terms mixed models or mixed effects that are used in other contexts such as the analysis of variance.

It is important to understand that the use of a mixed methods approach does not make research better or more valid than the use of either a qualitative or a quantitative approach."

"In nursing research, triangulation refers to the use of multiple sources to validate findings by the nursing researcher. It involves the combination of both quantitative and qualitative research methods within a single study."

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An overview of research designs relevant to nursing: Part 1: Quantitative research designs

Affiliation.

1 College of Health and Human Services, University of North Carolina at Charlotte, United States of America. [email protected]
PMID: 17653437
DOI: 10.1590/s0104-11692007000300022

This three part series of articles provides a brief overview of relevant research designs in nursing. The first article in the series presents the most frequently used quantitative research designs. Strategies for non-experimental and experimental research designs used to generate and refine nursing knowledge are described. In addition, the importance of quantitative designs and the role they play in developing evidence-based practice are discussed. Nursing care needs to be determined by the results of sound research rather than by clinical preferences or tradition.

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Perspect Clin Res
v.9(4); Oct-Dec 2018

Study designs: Part 1 – An overview and classification

Priya ranganathan.

Department of Anaesthesiology, Tata Memorial Centre, Mumbai, Maharashtra, India

Rakesh Aggarwal

1 Department of Gastroenterology, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

There are several types of research study designs, each with its inherent strengths and flaws. The study design used to answer a particular research question depends on the nature of the question and the availability of resources. In this article, which is the first part of a series on “study designs,” we provide an overview of research study designs and their classification. The subsequent articles will focus on individual designs.

INTRODUCTION

Research study design is a framework, or the set of methods and procedures used to collect and analyze data on variables specified in a particular research problem.

Research study designs are of many types, each with its advantages and limitations. The type of study design used to answer a particular research question is determined by the nature of question, the goal of research, and the availability of resources. Since the design of a study can affect the validity of its results, it is important to understand the different types of study designs and their strengths and limitations.

There are some terms that are used frequently while classifying study designs which are described in the following sections.

A variable represents a measurable attribute that varies across study units, for example, individual participants in a study, or at times even when measured in an individual person over time. Some examples of variables include age, sex, weight, height, health status, alive/dead, diseased/healthy, annual income, smoking yes/no, and treated/untreated.

Exposure (or intervention) and outcome variables

A large proportion of research studies assess the relationship between two variables. Here, the question is whether one variable is associated with or responsible for change in the value of the other variable. Exposure (or intervention) refers to the risk factor whose effect is being studied. It is also referred to as the independent or the predictor variable. The outcome (or predicted or dependent) variable develops as a consequence of the exposure (or intervention). Typically, the term “exposure” is used when the “causative” variable is naturally determined (as in observational studies – examples include age, sex, smoking, and educational status), and the term “intervention” is preferred where the researcher assigns some or all participants to receive a particular treatment for the purpose of the study (experimental studies – e.g., administration of a drug). If a drug had been started in some individuals but not in the others, before the study started, this counts as exposure, and not as intervention – since the drug was not started specifically for the study.

Observational versus interventional (or experimental) studies

Observational studies are those where the researcher is documenting a naturally occurring relationship between the exposure and the outcome that he/she is studying. The researcher does not do any active intervention in any individual, and the exposure has already been decided naturally or by some other factor. For example, looking at the incidence of lung cancer in smokers versus nonsmokers, or comparing the antenatal dietary habits of mothers with normal and low-birth babies. In these studies, the investigator did not play any role in determining the smoking or dietary habit in individuals.

For an exposure to determine the outcome, it must precede the latter. Any variable that occurs simultaneously with or following the outcome cannot be causative, and hence is not considered as an “exposure.”

Observational studies can be either descriptive (nonanalytical) or analytical (inferential) – this is discussed later in this article.

Interventional studies are experiments where the researcher actively performs an intervention in some or all members of a group of participants. This intervention could take many forms – for example, administration of a drug or vaccine, performance of a diagnostic or therapeutic procedure, and introduction of an educational tool. For example, a study could randomly assign persons to receive aspirin or placebo for a specific duration and assess the effect on the risk of developing cerebrovascular events.

Descriptive versus analytical studies

Descriptive (or nonanalytical) studies, as the name suggests, merely try to describe the data on one or more characteristics of a group of individuals. These do not try to answer questions or establish relationships between variables. Examples of descriptive studies include case reports, case series, and cross-sectional surveys (please note that cross-sectional surveys may be analytical studies as well – this will be discussed in the next article in this series). Examples of descriptive studies include a survey of dietary habits among pregnant women or a case series of patients with an unusual reaction to a drug.

Analytical studies attempt to test a hypothesis and establish causal relationships between variables. In these studies, the researcher assesses the effect of an exposure (or intervention) on an outcome. As described earlier, analytical studies can be observational (if the exposure is naturally determined) or interventional (if the researcher actively administers the intervention).

Directionality of study designs

Based on the direction of inquiry, study designs may be classified as forward-direction or backward-direction. In forward-direction studies, the researcher starts with determining the exposure to a risk factor and then assesses whether the outcome occurs at a future time point. This design is known as a cohort study. For example, a researcher can follow a group of smokers and a group of nonsmokers to determine the incidence of lung cancer in each. In backward-direction studies, the researcher begins by determining whether the outcome is present (cases vs. noncases [also called controls]) and then traces the presence of prior exposure to a risk factor. These are known as case–control studies. For example, a researcher identifies a group of normal-weight babies and a group of low-birth weight babies and then asks the mothers about their dietary habits during the index pregnancy.

Prospective versus retrospective study designs

The terms “prospective” and “retrospective” refer to the timing of the research in relation to the development of the outcome. In retrospective studies, the outcome of interest has already occurred (or not occurred – e.g., in controls) in each individual by the time s/he is enrolled, and the data are collected either from records or by asking participants to recall exposures. There is no follow-up of participants. By contrast, in prospective studies, the outcome (and sometimes even the exposure or intervention) has not occurred when the study starts and participants are followed up over a period of time to determine the occurrence of outcomes. Typically, most cohort studies are prospective studies (though there may be retrospective cohorts), whereas case–control studies are retrospective studies. An interventional study has to be, by definition, a prospective study since the investigator determines the exposure for each study participant and then follows them to observe outcomes.

The terms “prospective” versus “retrospective” studies can be confusing. Let us think of an investigator who starts a case–control study. To him/her, the process of enrolling cases and controls over a period of several months appears prospective. Hence, the use of these terms is best avoided. Or, at the very least, one must be clear that the terms relate to work flow for each individual study participant, and not to the study as a whole.

Classification of study designs

Figure 1 depicts a simple classification of research study designs. The Centre for Evidence-based Medicine has put forward a useful three-point algorithm which can help determine the design of a research study from its methods section:[ 1 ]

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Classification of research study designs

Does the study describe the characteristics of a sample or does it attempt to analyze (or draw inferences about) the relationship between two variables? – If no, then it is a descriptive study, and if yes, it is an analytical (inferential) study
If analytical, did the investigator determine the exposure? – If no, it is an observational study, and if yes, it is an experimental study
If observational, when was the outcome determined? – at the start of the study (case–control study), at the end of a period of follow-up (cohort study), or simultaneously (cross sectional).

In the next few pieces in the series, we will discuss various study designs in greater detail.

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COMMENTS

Clinical research study designs: The essentials - PMC
In clinical research, our aim is to design a study which would be able to derive a valid and meaningful scientific conclusion using appropriate statistical methods. The conclusions derived from a research study can either improve health care or result in inadvertent harm to patients.
Study Design and Methodology - Evidence Based Nursing ...
Study Design and Methodology. Evidence Based Nursing Practice. information on the process of evidence based practice for both student & professional nurse. tips & techniques for literature searches and reviews. Levels of Evidence. As the different study designs have different strengths, and weakness, they have been ranked in levels of evidence.
Research Design & Methodology - Research Methods in Nursing ...
Four types of qualitative research design often applied to nursing research are: Phenomenology - the study of human life experiences and how they appear in human consciousness. Grounded Theory - seeks to explain variations in social interactional and social structural problems and processes.
Understanding Research Study Designs - PMC
We use a variety of research study designs in biomedical research. In this article, the main features of each of these designs are summarized.
An overview of research designs relevant to nursing: Part 1 ...
Strategies for non-experimental and experimental research designs used to generate and refine nursing knowledge are described. In addition, the importance of quantitative designs and the role they play in developing evidence-based practice are discussed.
Study designs: Part 1 – An overview and classification
Research study design is a framework, or the set of methods and procedures used to collect and analyze data on variables specified in a particular research problem. Research study designs are of many types, each with its advantages and limitations.