Guide to Evidence-Based Nursing Practice for NPs

Every year, nurse practitioners provide health care for millions of individuals across the world. We use our expert knowledge to cure the sick. But where does this knowledge come from, and how do we know that it is right? The answer to that question lies in the realm of evidence-based practice informed by nursing science, epistemology, and philosophy. The purpose of this article is to thoughtfully explore the meaning behind evidence-based practice and to discuss the theoretical underpinnings of nursing care.

Evidence-Based Practice

Imagine you are a nurse practitioner working in an outpatient primary care clinic. A 33-year-old Caucasian female arrives with complaints of atypical depressive symptoms that are causing her to miss many days at work. You discover her symptoms have followed a temporal pattern over the past 4 years, and you diagnose her with seasonal affective disorder. How do you decide what treatment to prescribe? Evidence-based practice!

Evidence-based practice simply refers to combining research, clinical knowledge, and patient preferences to reach a health care decision. It emphasizes the use of the highest-quality information and deemphasizes the use of customs, opinions, or rituals to make a clinical judgment. The goal of evidence-based practice is simple: provide care that is safe, effective, and compassionate.

Nurses, nurse practitioners, and physicians all strive to implement evidence-based practice. The term evidence-based medicine arose in the 1970s when a group of physicians from the McMaster Medical School in Canada proposed a new learning theory. They believed that health care decisions should be based on external evidence. This idea was quite innovative at the time and launched the evidence-based practice movement.

The Evidence-Based Practice Movement

The movement began when the Cochrane Collaboration in the United Kingdom published a book in the early 1970s. This text shined a light on the lack of solid evidence backing decisions made by nurses and physicians. The book urged scientists to simply write summaries of their studies and give them health care providers to use. Today, the Cochrane Collaboration is well-known around the world for their systematic review publications.

The evidence-based practice movement gained popularity in 2001 when the Institute of Medicine (IOM) published Crossing the Quality Chasm, which exposed the unacceptable gap between scientific knowledge and clinical practice: “Between the health care we have and the care we could have lies not just a gap but a chasm.” They estimated that nearly 200,000 patients die from avoidable medical errors every year and 40% of patients do not receive scientifically proven treatments.

The IOM identified two interwoven problems causing this chasm. First, scientific knowledge is expanding rapidly, and second, this knowledge is becoming ever more complex. The amount of medical knowledge that a nurse practitioner must know today doubles every three years. In 2020, it will double every 73 days.

What did the IOM recommended as a solution? Evidence-based practice and more effective translational research. Crossing the Quality Chasm ignited a fire under healthcare professionals to more vigilantly use evidence-based practice. Efforts have also been made to more efficiently move research from dark labs and ivory towers into hospitals and clinics; however, it still takes 17 years for the latest research to be implemented into clinical practice. 17 years!

Evidence Hierarchy

Evidence-based practice demands the use of the “best” knowledge. The evidence hierarchy ranks sources of knowledge according to the strength of information they provide. Table 1 lists the levels and types of studies as ranked by nursing researchers Polit and Beck in their textbook Nursing Research. You will often see evidence hierarchies depicted as a pyramid.

The best evidence comes from Level I of the evidence hierarchy, which includes systematic reviews. Systematic reviews integrate the results from multiple studies using methodical and/or statistical procedures. When possible, nurse practitioners make their clinical judgments based on the findings of systematic reviews.

The least reliable evidence is found in Level VII, which includes options of authorities and expert committees. Generally, nurse practitioners should not use this as sufficient evidence to make a clinical decision, unless other levels of information are unavailable.

Table 1: Evidence Hierarchy
LevelTypes of Studies
Level I (Strongest)Systematic review of randomized-controlled trials or systematic review of nonrandomized trials
Level IISingle randomized-controlled trial or single nonrandomized trial
Level IIISystematic review of correlational or observational studies
Level IVSingle correlational or observational study
Level VSystematic review of descriptive, qualitative, or physiologic studies
Level VISingle descriptive, qualitative, or physiologic study
Level VII (Weakest)Opinions of authorities and expert committees
Adapted from Polit & Beck’s Nursing Research.

Systematic Reviews & Clinical Practice Guidelines

Systematic reviews and clinical practice guidelines are two types of resources that nurse practitioners use to access the “best” evidence. At the beginning of this article, we discussed a primary care nurse practitioner who needs to know the “best” treatment for a patient with seasonal affective disorder. Her answer most likely lies in either a systematic review or clinical practice guideline.

A systematic review is a scientific study that gathers multiple studies and analyzes them to draw a larger conclusion. The term systematic refers to methodical order and planning. When conducting a systematic review, the researcher uses transparent and structured steps in order to avoid bias and increase confidence in the findings. There are two main types of systematic reviews that each differs by the type of research they analyze and how they analyze it.

  • Meta-analysis: a scientific study that statistically analyzes a collection of quantitative studies. These studies objectively integrate the findings of multiple studies and use statistics to discover patterns that would be otherwise undetectable.
  • Metasynthesis: a scientific study that analyzes a collection of qualitative studies and summarizes these findings in a narrative format.

A clinical practice guideline is similar to a systematic review in that it distills a large amount of research into a short, easy to understand format. Usually, clinical practice guidelines summarize one or more systemic reviews on any given diagnosis or intervention. Nurse practitioners use these documents to guide their decision making. In the United States, clinical practice guidelines are accessed through the National Guideline Clearinghouse.

More information about systematic reviews can be found in Holly, Salmon, and Saimbert’s Comprehensive Systematic Review for Advanced Nursing Practice and Polit and Beck’s Nursing Research.

Principles of Evidence-Based Practice

A nurse practitioner is implementing evidence-based practice when she prescribes a treatment for a patient that is substantiated by scientific research. Often, nurse practitioners look for an experimental study that compares the efficacy of a treatment with an untreated control group. The core principles of evidence-based practice include:

  • Formulating a clinical question
  • Locating relevant research
  • Critically evaluating the quality of this research
  • Applying the research
  • Reevaluating the application of the research

Nursing Science

Defining nursing science is complicated by a dispute as to whether nursing is a pure science or an applied science. Pure science refers to seeking and discovering new knowledge. Scientists studying the human eye to understand vision is an example of a pure science endeavor. On the other hand, applied science refers to the practical use of knowledge. Developing contact lenses and eyeglasses is an example of an applied science endeavor.

More recently, nurse experts have concluded that nursing is a pure science that possesses its own body of knowledge. Our knowledge focuses on factors that affect human wellness. Nursing science is comprised of more than facts. It embraces multiple paradigms of knowing beyond traditional empirical research such as creativity, debate, diversity, and open inquiry.

The definition of nursing science that has always made the most sense to me is written by Stevenson and Woods in 1986. They wrote, “Nursing science is the domain of knowledge concerned with the adaptation of individuals and groups to actual or potential health problems, the environments that influence health in humans, and the therapeutic interventions that promote health and affect the consequences of illness.”

More on nursing science can be found in Roy and Jones’ Nursing Knowledge Development and Clinical Practice: Opportunities and Directions and Zaccagnini and White’s Doctor of Nursing Practice Essentials

Definition of Nursing

To understand nursing science, you must understand the definition of nursing itself. The American Nurses Association defines nursing as, “The protection, promotion, and optimization of health and abilities, prevention of illness and injury, facilitation of healing, alleviation of suffering through the diagnosis and treatment of human response, and advocacy in the care of individuals, families, groups, communities, and populations.”

Depending on their personal philosophical perspective, nurse experts have defined nursing in different ways. Other nurse theorists have defined nursing as:

  • Actions taken by nurses and the outcomes achieved by those actions (Fawcett)
  • A performing art centered around nursing knowledge (Parse)
  • The use of nursing knowledge to improve the human condition (Rogers)
  • A process of nursing interactions within and between systems (King)
  • The study of promoting wellbeing (Reed)

The American Association of Colleges of Nursing elaborates upon these definitions by describing the four key focus areas of nursing practice. These focus areas differentiate the nursing discipline; we possess a special knowledge of human beings, human behavior, health, and human interaction with the environment. The four focus areas include:

  • Principles that govern life-process, well-being, and optional function of human beings;
  • Patterns among human interaction and the environment in critical life situations;
  • Actions or processes that make positive changes in health statuses; and,
  • Wholeness and health of human beings.

For more information on the definition of nursing, read Cody’s Philosophical And Theoretical Perspectives For Advanced Nursing Practice.

Is Nursing Science Different than Medical Science?

The answer to this question is, “Yes, well kinda, I guess not really, but yes.” Medical science emphasizes the concepts of diagnosis and treatment of disease. Nursing science emphasizes the concept of a human’s response to sickness. I would argue that both professionals emphasize both concepts. We overlap at many points and the largest difference lies in our scope of practice.

So what does this mean for nurse practitioners? We diagnose and treat disease, and we focus on a person’s response to their illness. Some experts assert that when nurse practitioners treat a patient they uniquely begin with the human being rather than the disease, and they place the patient’s values and goals ahead of their own. I have known physicians who do the same.

So, does being a nurse practitioner fundamentally differ from being a physician? The cheeky response would be, “Depends on what state you live in.” Something that is beautiful about being a nurse practitioner is that our field grew from the principles that overlap between nurses and physicians. We’ve got the best of both worlds!

For more information on this topic please see Chapter 1 of Zaccagnini and White’s Doctor of Nursing Practice Essentials.

Nursing Epistemology

Nursing science has its foundations in various forms of knowledge: philosophical, ethical, historical, biopsychosocial, and organizational. Epistemology refers to the study of knowledge. A mature nurse practitioner understands the value of different forms of knowledge and uses each one to inform his or her daily practice. This section elaborates upon each type of knowledge and lists resources for further reading.

Philosophical Knowledge

A philosophical framework serves as a foundation and structure for any body of knowledge. Your personal philosophy is the way you explain your world and the enduring set of principles you hold. A philosophy frames the manner in which you approach problems, and it underpins science, theory, and research.

Nursing science is primarily directed by three philosophical orientations: positivism, antipositivism, and postpositivism. These orientations are defined as follows.

  • Positivism (also known as empiricism) encompasses hard or natural sciences
  • Antipositivism embraces soft or interpretive human sciences
  • Postpositivism (also known as contemporary empiricism) acknowledges that social and historical contexts affect knowledge and that a complete understanding of knowledge includes both observable reality and the human experience.

Nurse practitioners may vary in their individual philosophies, but looking at the profession as a whole reveals the common themes of (1) holism, (2) quality of life, and (3) the relativity of truth based on each person’s perceptions. Both the nurse practitioners of today and tomorrow have the opportunity to define and refine the philosophies that shape our theories, research, and practice: an awesome responsibility!

For a more detailed exploration of nursing philosophy consider reading Philosophies And Theories For Advanced Nursing Practice by Butts and Rich or Philosophical And Theoretical Perspectives For Advanced Nursing Practice by Cody. You can also read a quick summary of nursing philosophy in Doctor of Nursing Practice Essentials by Zaccagnini and White.

Ethical Knowledge

In health care, ethical concerns are complex and varied. Through their MSN and DNP programs, nurse practitioners are prepared to address ethical dilemmas that may arise within our profession or in clinical practice. The core of modern nurse practitioner ethics rejects the old medical ethics of paternalism and instead promotes respect for individual autonomy.

Ethical knowledge applies to nursing research as well. In their Code of Ethics for Nurses with Interpretive Statements, The American Nurses Association asserts that nurse practitioners have the ethical obligation to protect human rights. Specifically, when conducting scientific research, nurse practitioners must protect their participant’s right to privacy, fair treatment, and self-determination.

To learn more about nursing ethics, I suggest reading Butts and Rich’s Nursing Ethics: Across the Curriculum and Into Practice. Another great read that focuses on general bioethics is Vaugn’s Bioethics: Principles, Issues and Cases. My personal favorite text on this topic is Orentlicher, Bobinski, and Hall’s Bioethics Public Health Law.

Historical Knowledge

As George Santayana shrewdly stated, “Those who cannot remember the past are condemned to repeat it.” History provides context to our discipline, and information interpreted without an understanding of its context results in misinformation and erroneous conclusions.

Only 50 years ago, Dr. Loretta Ford, a public health nurse, established the first nurse practitioner school and broke ground on a new, revolutionary profession. Dr. Ford envisioned an innovative role for nurses where they could assess, diagnose, and even treat medical conditions without physician oversight.

Like a true trailblazer, her vision was a radical one: at that time, nurses could not even use stethoscopes! Fortunately, her idea was just crazy enough to work. In 1965, Dr. Ford and the University of Colorado started the nation’s first nurse practitioner program. Today, nurse practitioners act as independently licensed health care providers. They offer an high-quality, cost-effective solution to increasing access to healthcare for millions of Americans.

For detailed information on nursing history read Fairman’s Making Room in the Clinic: Nurse Practitioners and the Evolution of Modern Health Care. A succinct overview of our history can be found in Part I of Nurse Practitioners: The Evolution and Future of Advanced Practice. One of my favorite texts on historical knowledge is A History of Nursing Ideas by Andrist, Nicholas, and Wolf.

Biopsychosocial Knowledge

What is extraordinarily special about nurse practitioners is that they are educated in both biophysical and psychosocial knowledge. Our profession integrates information accumulated from a variety of disciplines including biology, physiology, psychology, and sociology. In fact, this beautiful, holistic blend of knowledge is what brings many people to the field.

As a freshman in college, I was pretty much clueless about what I wanted to do for the rest of my life. I ended up taking a personality test that left me ever more baffled. It told me that the best four professions for me were graphic designer, physician, researcher, and criminal profiler. As I was searching through majors I stumbled upon nursing and noticed that I would be required to take a variety of natural science, social science, and research-oriented courses. Bingo! A perfect blend of empirical and human science.

Sadly, the public often misunderstands nursing education. I once had a family member criticize my profession for “not taking any real science classes.” Before that moment, I had mistakenly assumed that people regarded my career as highly as I did. My gut response was, “What do you think I studied for 8 years?”

To set the record straight, nurses and nurse practitioners undergo extensive education in natural, social, and research science. Table 2 lists some of the courses within these categories that I was required to take in my BSN, MSN, and DNP programs.

Table 2: Sample Science Courses from Nursing Curricula
Natural ScienceSocial ScienceResearch Science
Anatomy & PhysiologyPhysical ChemistryMicrobiologyPathophysiologyAdvanced PathophysiologyNeurosciencePharmacologyEpidemiologyIntroduction to PsychologySocial PsychologyChild DevelopmentAbnormal PsychologyHealth and CultureHealth Behavior ChangeEconlomics of HealthcareOrganizational BehaviorGeneral StatisticsBiostatisticsEvidence-Based PracticeIntegration of EvidenceTranslational ResearchScientific Underpinnings of PracticeNursing TheoryHealth Ethics
This is a general list adapted from my personal experience. Each school differs in what courses are offered. This list excludes clinical courses and any courses specific to my psychiatry specialty. I attended Xavier University for my BSN, Vanderbilt University for my MSN, and DeSales University for my DNP.

Organizational Knowledge

Organizational knowledge and systems thinking add an essential dimension to nursing science. Nurse practitioners understand that organizations are systems in motion with complex relationships between many different parts. Our knowledge encompasses all levels (micro, macro, mega, and meta) of organizational systems, and we integrate this understanding to seek solutions to the major problems impacting patient care.

  • Microsystem: direct patient care
  • Macrosystem: hospitals, long-term care facilities, clinics
  • Megasystem: American health care system
  • Metasystem: economic, political and social level of society

Nurse practitioners use organizational knowledge to function effectively within complex systems and to provide high-quality care. For example, we acknowledge that a majority of medication errors are not the fault of any one person or event. Rather, these errors are the result a flawed system of medication administration used by the entire organization. Nurse practitioner education prepares us to critically analyze the healthcare system, discover inefficiencies and errors, and craft solutions.

In my DNP program I read a fascinating book about systems thinking by Peter Senge titled, The Fifth Discipline: The Art & Practice of The Learning Organization. Chapter 2 in Zaccagnini and White’s Doctor of Nursing Practice Essentials describes how nurse practitioners can use organizational knowledge to improve the health care system. Finally, a popular book by Clayton Christensen titled The Innovator’s Prescription: A Disruptive Solution for Health Care critiques the current means of healthcare delivery.

Nursing Theory

A nursing theory is a collection of related concepts that guide a systemic view of phenomena. Theory-guided practice refers to the use of theories to understand patients and plan interventions. Nursing theory improves our discipline by giving it a structure and unity by which we examine our effectiveness.

Most often, theories are classified by their philosophical perspective and scope. In nursing, we primarily use grand theories and middle-range theories.

  • Grand theories are the highly abstract and the widest in scope. They are most often used to describe general concepts or propositions, and they are not meant for empirical testing.
  • Middle-range theories are concrete and offer specific explanations about phenomena of interest. The concepts of these theories are operationally defined and can be empirically tested.

Both grand theories and middle-range theories encompass either one or more of four types of theory: descriptive, explanatory, predictive, and prescriptive. Nursing Theory Network defines these types as:

  • Descriptive theory: identifies properties and components of a discipline.
  • Explanatory theory: identifies how the properties and components relate to one another.
  • Predictive theory: conjectures the relationships between components of a phenomenon and predicts when the phenomena will occur.
  • Prescriptive theory: addresses therapeutics and consequences of interventions.

Theory-Guided Practice

Nurse practitioners learn about theory during their education, and they use it to guide their practice in order to achieve better patient outcomes. Zaccagnini and White eloquently write, “Considering the often fragmented, inefficient, and disorganized care typical of the current healthcare system, we need nursing theory-guided practice to provide a coherent antidote.”

Nurse practitioners undergo extensive education on practice theory and are expected to understand a variety of different theories. Using only one theory to guide a person’s entire practice narrows own vision and forces every patient into a single mold. Nurse practitioners select the most appropriate conceptual model for each particular situation.

To choose a theory to guide their practice, nurse practitioners follow the process outlined by Janet Kenney (See Chapter 31 in Philosophical and Theoretical Perspectives for Advanced Nursing Practice).

  • Consider your personal values and beliefs about nursing, patients, health, and the environment.
  • Examine your underlying assumptions, values, and beliefs of various nursing models.
  • Identify several models that are congruent with your own values and beliefs.
  • Practice applying the models and theories to different patient situations.

Examples of Nursing Theories

Table 3 lists nursing theories organized by topic. Table 4 lists theories by other disciplines that are commonly employed by nursing professionals. Nurse practitioners, especially those with DNP degrees, take courses that focus on understanding and utilizing these theories to improve healthcare delivery.

For a high-level summary of these theories see Chapter 1 of Zaccagnini and White’s Doctor of Nursing Practice Essentials. For a detailed explanation of the theories see Parts III and IV of Butts and Rich’s Philosophies And Theories For Advanced Nursing Practice. Additional information can be found on the Nursing Theory Network website.

Table 3: Nursing Theories
FocusTheory or Model
Nursing goals and functionsFlorence Nightingale’s environmental model of nursingVirginia Henderson’s 14 components of basic nursing careDorothy Johnson’s behavioral system modelNola J. Pender’s health promotion modelIda Jean Orlando’s nursing process theoryPeplau’s theory of interpersonal relations in nursing
Systems thinkingRoy adaptation modelKing conceptual system and theory of goal attainmentNeuman systems model
Human existenceBarrett’s power as knowing participation in changeNewman’s theory of health as expanding consciousnessRosemarie Rizzo Parse’s humanbecoming school of thought
Competencies and skillsBrenner’s from novice to expertAmerican association of critical care nurse’s synergy model for patient careTravelbee’s human-to-human relationship model
CaringThe nursing as caring theory by Boykin and SchoenhoferWatson’s theory of human caringSwanson’s middle-range theory of caringDuffy’s quality-caring model
CultureCampinha-Bacote modelGiger and Davidhizer modelLeininger’s culture care diversity and universality theorySpector’s health traditions modelPurnell model for cultural competency
This list is adapted from Part IV Chapters 17-22 of Butts and Rich’s Philosophies And Theories For Advanced Nursing Practice.
Table 4: Other Theories Used in Nurse Practitioner Practice
FocusTheory or Model
Complexity scienceComplex adaptive systems
Critical theory and emancipatory knowingHabermas’s critical social philosophyFreire’s theory of human liberation
EthicsNatural-Law TheoryRights TheoryDeontologyConsequentialismCommunitarianism
EducationalBehaviorist learning theoryCognitive learning theoryGestalt theoryCognitive development theoryInformation-processing theorySocial learning theorySocial constructivismPsychodynamic learning theoryHumanistic learning theory
Health behaviorThe health belief modelTheory of reasoned actionTheory of planned behaviorIntegrated behavioral modelTranstheoretical model and stages of changeSocial cognitive theorySocial ecological models
InterpersonalHarry Stack Sullivan’s theory of interpersonal relationsInterpersonal relations theoryExistentialismPositive psychologyTranspersonal psychology
Organizational behavior and leadershipBureaucratic theoryHuman resource theoryContingency theoryGeneral systems theoryChange theoryTheories X, Y, and Z
This list is adapted from Part III Chapters 6-16 of Butts and Rich’s Philosophies And Theories For Advanced Nursing Practice.

Recommendations for Further Reading

Want to learn more about nursing science and evidence-based practice? These are some of my favorite books.

  • Nursing Research by Polit and Beck. My BSN, MSN, and DNP programs all required this textbook. It is an excellent resource with particularly helpful tables, graphs, and illustrations that explain complex research topics.
  • Doctor of Nursing Practice Essentials by Zaccagnini and White. This is one of my favorite nurse practitioner books. The authors write clearly, succinctly, and confidently. Chapters one and three discuss nursing science and evidence-based practice from a nurse practitioner’s standpoint.
  • Comprehensive Systematic Review for Advanced Nursing Practice by Holly, Salmond, and Saimbert. This is an excellent book if you are interested in learning about or conducting a systematic review. I used this book through every step of my DNP project.
  • Philosophies And Theories For Advanced Nursing Practice by Butts and Rich. These authors offer a detailed guide to nursing theories and the philosophical foundation of our profession. I purchased this book on my own accord during my MSN program. It helped me write my assigned papers and answer the question, “What theoretical framework did you use for this study?”
  • Nurse Practitioners: The Evolution and Future of Advanced Practice by Sullivan-Marx, McGivern, Fairman, and Greenberg. First and foremost, this book is awesome! It provides a great overview of nurse practitioner history. Remember, “Those who cannot remember the past are condemned to repeat it.”
Dr. Melissa DeCapua, DNP, PMHNP-BC

Dr. Melissa DeCapua, DNP, PMHNP-BC


Melissa DeCapua is a board-certified psychiatric nurse practitioner who graduated from Vanderbilt University. She has a background in child and adolescent psychiatry as well as psychosomatic medicine. Uniquely, she also possesses a bachelor’s degree in studio arts, which she uses to enhance patient care, promote the nursing profession, and solve complex problems. Melissa currently works as the Healthcare Strategist at a Seattle-based health information technology company where she guides product development by combining her clinical background and creative thinking. She is a strong advocate for empowering nurses, and she fiercely believes that nurses should play a pivotal role in shaping modern health care. For more about Melissa, check out her blog and follow her on Twitter @melissadecapua.

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