Measurement and Scales in Quantitative Method Introduction
Measurement is a foundational element of quantitative research, serving as the means to quantify attributes of persons, objects, or events. In nursing research, measurement provides consistency and a meaningful representation of patient data, facilitating decision-making, planning, and evaluating nursing interventions. This article explores the principles and practices of measurement in nursing, the various scales of measurement, the importance of measurement in nursing research, and the contributions of key nursing scientists to this field.
Measurement and Scales
Measurement focuses on the quantification of a characteristic or attribute of a person, object, or event. It involves a systematic process that uses established rules to assign numbers to persons, objects, or events, representing the amount or kind of a specified attribute. The goal of measurement is to provide consistent and meaningful information about an attribute, ensuring that the same measurement process or instrument yields comparable results over time.
Measurement Attributes
Effective measurement involves identifying and specifying common aspects of attributes for meaningful interpretation and categorization. Ambiguity and confusion arise when the meaning of any measurement is not clearly defined. Measurement relevance is determined by an explicit or implicit theoretical framework that provides structure to the phenomenon being studied. Qualitative assessments also apply measurement principles by providing meaning and interpretation through the description and categorization of phenomena, highlighting that measurement is essential in both qualitative and quantitative research.
Importance of Measurement
Measurement is crucial in all nursing settings. Nurses rely on measurement instruments to determine patient attributes, such as clinical laboratory and physical examination results, which inform patient needs and care planning. Nurse researchers use a wide range of clinical, laboratory, observational, and questionnaire measures to study phenomena of interest. Additionally, nurse educators use measurement instruments and test scores to assess students’ mastery of skills and knowledge. In essence, measurement underpins all aspects of nursing practice, research, and education.
Levels of Data Scales
Measurement scales provide the rules for assigning numbers to objects to represent the amount or kind of an attribute. In nursing research, four primary types of measurement scales are used: nominal, ordinal, interval, and ratio scales.
- Nominal Scale: This scale places attributes into defined categories according to a specific property. Numbers assigned to nominal level data have no hierarchical meaning but represent an object’s membership in one of a set of mutually exclusive, exhaustive, and unorderable categories. For example, categorizing participants in a study as either male or female is nominal measurement.
- Ordinal Scale: In ordinal scale measurement, rules are used to assign rank order to an attribute characterizing a person, object, or event. It involves the rank ordering of objects into hierarchical categories according to relative amounts of the attribute studied. An example is the grading of heart murmurs from 1 to 6, where each grade represents a different intensity level. However, the intervals between ranks are not equal or necessarily measurable.
- Interval Scale: This scale represents continuous measurement with equal numerical distances between adjacent scores, reflecting equal amounts of the attribute being measured. However, the absolute amount of the attribute is not known because the zero point is arbitrary. An example is temperature measurement in Celsius or Fahrenheit, where zero does not indicate the absence of temperature but rather an arbitrary point on the scale.
- Ratio Scale: Ratio scales provide the same information as interval scales but include a true zero point, indicating the absence of the attribute being measured. Volume, length, and weight are commonly measured using ratio scales, making this level of measurement the most precise and informative.
There is some controversy over the appropriate use of statistical procedures for different levels of measurement scales. Some researchers argue that only non-parametric statistical methods should be applied to nominal or ordinal data, while parametric methods are suitable for interval and ratio data. For example, Likert scales, commonly used in nursing research to measure attitudes or opinions, are often considered ordinal. However, it has become accepted practice to treat Likert scale data as interval-level data for statistical analysis.
Other Levels from Other Disciplines
Nursing, as a multidisciplinary field, frequently borrows measurement instruments from other disciplines, such as education, psychology, sociology, and physiology. This practice reflects nursing’s comprehensive approach to care, which encompasses both biological and psychosocial aspects. However, there are limitations to this approach. Instruments developed in other fields may not be well-suited for nursing-specific contexts or may be cumbersome to use in clinical settings.
Nursing studies often involve diverse populations, such as children, frail elderly patients, and culturally diverse groups. The lack of nursing-specific instruments to measure important variables from a nursing perspective has been a challenge. Research on families, communities, and systems has also been hindered by the absence of effective tools to assess group and system variables in the context of nursing (Strickland, 1995).
Research and Nursing Bureau of Health
In the 1970s, the nursing profession recognized the need for more rigor in developing measurement instruments. In 1974, the Division of Nursing, Bureau of Health Manpower, and Health Resources Administration awarded a contract to compile nursing research instruments. The resulting two-volume publication, “Instruments for Measuring Nursing Practice and Other Health Care Variables,” prioritized instruments focused on nursing practice and patient variables rather than nurse variables. This effort marked an important milestone in nursing measurement, providing a comprehensive set of clinically focused instruments developed or used by nurses.
Nursing Research and Two Groups of Nursing Scientists
Two groups of nursing scientists emerged as leaders in developing measurement as an area of emphasis in nursing research during the late 1970s and early 1980s.
- At the University of Arizona-Tucson, Ada Sue Hinshaw and Jan Arwood focused on refining instruments for clinical settings. They established the first postdoctoral program in nursing instrumentation and measurement and hosted annual national conferences on nursing measurement. These conferences provided a forum for nurses to discuss measurement issues and present information on instruments used in their studies.
- At the University of Maryland, Ora Strickland and Carolyn Waltz concentrated on defining measurement principles and practices to enhance the rigor of nursing research. Their assessments of nursing research revealed that nurse investigators often neglected issues of reliability and validity when selecting and developing instruments and overly relied on paper-and-pencil self-report measures rather than biological measures as indicated by their studies’ conceptual frameworks (Strickland & Waltz, 1986).
The Maryland group published the first measurement textbook for nurses, “Measurement in Nursing Research,” and developed a measurement project funded by the Division of Nursing, Department of Health and Human Services. This project trained over 200 nurse researchers to develop and test instruments for use in clinical or educational settings, resulting in the award-winning four-volume series, “Measurement of Nursing Outcomes.”
In 1993, Ora Strickland initiated the “Journal of Nursing Measurement,” with Ada Sue Hinshaw as co-editor, providing a dedicated platform for the discussion, development, and dissemination of nursing measurement instruments.
Measurement Principles and Practices in Nursing Research
The efforts of these nurse scientists helped to build a foundation for rigorous measurement practices in nursing research. These practices include:
- Reliability and Validity: Ensuring that instruments used in nursing research are reliable (consistently measure what they intend to measure) and valid (accurately measure the intended attribute).
- Appropriate Use of Measures: Encouraging the use of instruments that are appropriate for the nursing context, including biological measures when indicated.
- Development of Nursing-Specific Instruments: Creating tools that are suitable for diverse populations and settings in nursing, such as children, the elderly, and culturally diverse groups.
Outcomes
Since the late 1970s, the nursing profession has made significant progress in developing and refining measurement tools for various settings. Nurses have created new instruments and adapted those developed in other disciplines for use in nursing studies. However, challenges remain, particularly in developing instruments that adequately address the unique needs and contexts of nursing research.
Conclusion
Measurement is a critical aspect of nursing research, providing the quantitative data necessary for patient care, clinical decision-making, and evaluating the effectiveness of nursing interventions. The development of reliable and valid measurement instruments tailored to the needs of nursing research is crucial for advancing the profession. As the field continues to grow, ongoing efforts to refine measurement practices will enhance the quality and impact of nursing research, ultimately improving patient outcomes and advancing the science of nursing.