Terms and definitions

“Epidemiology is so beautiful and provides such an important perspective on human life and death, but an incredible amount of rubbish is published.” (Taubes 2007)

Sir Richard Peto, Professor of Medical Statistics & Epidemiology

1.1.1 Epidemiology

The origin of the word epidemiology is unknown, but it is derived from the Greek words meaning ´study upon populations´ (epi = upon, demos = people, ology = study). Although few excellent epidemiological investigations were conducted earlier, most principles of epidemiology began to form only in the second half of the 20th century. The latter part of the 20th century was an era of rapid growth in terms of epidemiological concepts (Rothman et al.

2008). MacMahon and Pugh (MacMahon & Pugh 1970) defined epidemiology as the study of the distribution and determinants of disease in man, whereas Miettinen as the principles of studying the occurrence of illness and related states and events, including those of health care (“occurrence research”) (Miettinen 1985).

Nowadays, the scope of epidemiology has widened substantially. Epidemiology includes 1) the methods for measuring the health of groups and for determining the attributes and exposures that influence health; 2) the study of the occurrence of disease in its natural habitat (rather than in the controlled laboratory environment); and 3) the methods for the quantitative study of the distribution, variation, and determinants of health-related outcomes in specific groups (populations) of individuals, and the application of this study to the diagnosis, treatment, and prevention of these states or events. Epidemiology can be divided into 1) descriptive (observational) epidemiology, 2) analytical epidemiology, and 3) clinical epidemiology. Clinical epidemiology (evidence-based medicine) serves as ´a basic science for

clinical medicine´ and encompasses diagnosis and treatment in patient care, including evaluation of various approaches in terms of techniques and methods, algorithms and decision rules as well as the organisation and provision of services (Sackett et al. 1991).

Epidemiology is characterised by an empirical, quantitative and stochastic approach to the study of health-related phenomena. Empirical approach means that observations are systematically collected. Quantitative and stochastic nature means that observations are treated numerically and occurrence and effects can be presented as probabilities. These characteristics form the basis for the epidemiological concept of cause. Generally, a cause in epidemiology is defined as a factor that alters the probability of occurrence of the consequence. Causal relations investigated in epidemiology are typically complex, multifactorial networks and their elucidation is demanding due to limitations in easily applicable concepts and measurements. A risk factor (when used in the wide sense on not necessarily implying causality as in this study) can be defined as an antecedent event, condition, or characteristic associated with an outcome. Sometimes a distinction is made between causal factors (with well established etiological role), correlates (without a causal effects), risk factors (incompletely understood possible causal factors) and risk indicators (predictive factors regardless of possible causal involvement). (Rothman et al. 2008)

Epidemiology is closely related to several other disciplines including (clinical) medicine, statistics and demographics. Both medicine and epidemiology cover health and disease. The focus in clinical medicine is an individual (patient), whereas epidemiology looks at the population level. Clinical epidemiology (evidence-based medicine) is in between. Statistics has provided tools for epidemiological research, whereas many study designs used in epidemiology are originally from demographical research.

This dissertation covers prevalence, impact and risk factors of nocturia. The natural history of nocturia will be assessed in our future work. Despite lacking the prospective aspect of nocturia here, this dissertation covers the other most important viewpoints of epidemiology, thereby justifying the title ´Epidemiology of nocturia´.

1.1.2 Lower urinary tract symptoms and nocturia

Earlier research on urinary symptoms has focused on LUTS on men and on SUI in women.

Traditionally, nocturia has often been attributed to aging or childbirth in women, and to LUTS suggestive of benign prostatic hyperplasia (BPH) in men. In recent years ´overactive bladder symptoms´ and their treatment in both sexes has commanded attention worldwide (Ouslander 2004, Cartwright et al. 2008). Nocturia was for a long time a neglected topic in the medical literature (Barker & Mitteness 1988). However, it has recently been recognised as a clinical entity in its own right (Weiss & Blaivas 2000, van Kerrebroeck et al. 2002), and currently there is a growing interest in nocturia (Figure 1).

Generally, the definition of a disease/condition/symptom is a critical factor in evaluating its epidemiology; nocturia is no exception to this rule (Hunskaar 2005). To facilitate discussion and research related to LUTS, the ICS has produced standardisation reports. The ICS revised its Standardisation Report of lower urinary tract function terminology in 2002 (Abrams et al.

2002). The Report has been already revised further and the discussion/debate is ongoing (Abrams et al. 2009).

In the 2002 Standardisation Report (Abrams et al. 2002), LUTS were divided into three major groups (storage, voiding and post-micturation symptoms), while related symptoms were further divided into four groups (symptoms associated with sexual intercourse, symptoms associated with pelvic organ prolapse, genital and lower urinary tract pain, and genitor-urinary pain syndromes and symptom syndromes suggestive of lower genitor-urinary tract dysfunction).

Voiding symptoms include slow stream, splitting/spraying, intermittent stream, hesitancy, straining and terminal dribble, whereas post micturition symptoms include feeling of incomplete emptying and post micturition dribble (Abrams et al. 2002). The FINNO Study aims to evaluate especially urinary storage symptoms such as nocturia and urinary urgency.

The ICS recognises four kinds of ´urinary storage symptoms´, (formerly ´irritative´

symptoms):

1. Increased daytime frequency (formerly urinary frequency, pollakisuria) defined as the complaint by the patient who considers that he/she voids too often by day.

2. Nocturia defined as the complaint that the individual has to wake at night one or more times to void

3. Urgency defined as the complaint of a sudden compelling desire to pass urine which is difficult to defer.

4. Urinary incontinence is the complaint of any involuntary leakage of urine.

It has been proposed that the difference between nocturia and night-time frequency should be clarified as shown in Figure 2 (Homma 2008).

Figure 2. Newly defined nocturia does not include voiding from the time of going to bed until the time of falling asleep, waking-and-voiding not due to a desire to void, or voiding from the time of waking until the time of rising from bed. (Figure including figure legend reprinted with permission from Homma. Lower urinary tract symptomatology: Its definition and confusion. Int J Urol 2008;15:35-43).