Common quantitative methods

This chapter provides an overview of the meaning, purpose and issues related to quantitative research designs, and presents the common approaches used to answer a variety of nursing and midwifery questions. Related issues such as sampling, data collection, assessment of measurement instruments and data analysis are discussed in Chapters 10-13. The focus is on providing research consumers with the information to evaluate quantitative studies critically. Quantitative research refers to studies where the variables of interest are measurable and the results are quantifiable and coded as numerical data. Figure 9.1 (Bryman & Cramer 2005) shows one way of looking at quantitative research and shows how it can be divided into two branches: survey (also called observational and correlational) and experimental. Both branches include a range of designs but both are capable of testing theory by asking research questions through the specific identification of independent and dependent variables, the formulation of hypotheses and their testing using statistical methods. However, these two branches are not equally capable of discerning cause and effect between variables and there is, essentially, a hierarchy in the ability to do this as illustrated in Table 9.1. There are three major categories of designs along the quantitative continuum: observational, quasi-experimental and experimental. Each category includes a range of designs. Choice of a design relates to the research question or hypothesis, the amount of control a researcher can have and study feasibility. Much of what we know as quantitative research methods have been designed by the discipline of epidemiology. Interestingly, one of the first epidemiologists was Florence Nightingale. Statistical tests which she developed to produce evidence about outcomes for wounded and sick soldiers at the Crimea were recognised at the International Congress of Statistics in 1860 (McDonald 2001). Modern epidemiology (from Greek, meaning 'the study of people') is defined by the Australasian Epidemiological Association (20 1 O) as the study of diseases in populations. Epidemiology has three main aims: to describe disease patterns in human populations; to identify the causes of diseases (also known as aetiology); and to provide data essential for the management, evaluation and planning of services for the prevention, control and treatment of disease. There are many excellent books on epidemiology written expressly for nurses and midwives; a recent example is Epidemiology for Advanced Nursing Practice by Kiran Macha and John McDonough, published in 2011 by Joyce and Bartlett Learning in the USA. Any midwife or nurse undertaking quantitative research is well advised to learn the basics of epidemiology