Research studies usually include terms that must be carefully and precisely defined, so that others know exactly what has been done and there are no ambiguities. Two types of definitions can be given: conceptual definitions and operational definitions.
Loosely speaking, a conceptual definition explains what to measure or observe [what a word or a term means for your study], and an operational definitions defines exactly how to measure or observe it.
For example, in a study of stress in students during a university semester. A conceptual definition would describe what is meant by ‘stress.’ An operational definition would describe how the ‘stress’ would be measured.
Definition 2.1 [Conceptual definition] A conceptual definition articulates what exactly is to be measured or observed in a study.
Definition 2.2 [Operational definition] An operational definition articulates how to capture [identify, create, measure, assess etc.] the value.
Sometimes the definitions themselves aren’t important, provided a clear definition is given. Sometimes, commonly-accepted definitions exist, so should be used unless there is a good reason to use a different definition [for example, in criminal law, an ‘adult’ in Australia is someone aged 18 or over].
Sometimes, a commonly-accepted definition does not exist, so the definition being used should be clearly articulated.
Example 2.2 [Operational and conceptual definitions] Players and fans have become more aware of concussions and head injuries in sport. A Conference on concussion in sport developed this conceptual definition [McCrory et al. 2013]:
Concussion is a brain injury and is defined as a complex pathophysiological process affecting the brain, induced by biomechanical forces. Several common features that incorporate clinical, pathologic and biomechanical injury constructs that may be utilised in defining the nature of a concussive head injury include:
Concussion may be caused either by a direct blow to the head, face, neck or elsewhere on the body with an “impulsive” force transmitted to the head.
Concussion typically results in the rapid onset of short-lived impairment of neurological function that resolves spontaneously. However, in some cases, symptoms and signs may evolve over a number of minutes to hours.
Concussion may result in neuropathological changes, but the acute clinical symptoms largely reflect a functional disturbance rather than a structural injury and, as such, no abnormality is seen on standard structural neuroimaging studies.
Concussion results in a graded set of clinical symptoms that may or may not involve loss of consciousness. Resolution of the clinical and cognitive symptoms typically follows a sequential course. However, it is important to note that in some cases symptoms may be prolonged.
While this is all helpful… it does not explain how to identify a player with concussion during a game.
Rugby decided on this operational definition [Raftery et al. 2016]:
… a concussion applies with any of the following:
The presence, pitch side, of any Criteria Set 1 signs or symptoms [table 1]… [Note: This table includes symptoms such as ‘convulsion,’ ‘clearly dazed,’ etc.];
An abnormal post game, same day assessment…;
An abnormal 36–48 h assessment…;
The presence of clinical suspicion by the treating doctor at any time…
Example 2.3 [Operational and conceptual definitions] Consider a study requiring water temperature to be measured.
An operational definition would explain how the temperature is measured: the thermometer type, how the thermometer was positioned, how long was it left in the water, and so on.
In contrast, a conceptual definition might describe the scientific definition of temperature.
Example 2.4 [Operational definitions] Consider a study measuring stress in first-year university students.
Stress cannot be measured directly, but could be assessed using a survey [like the Perceived Stress Scale [PSS] [Cohen et al. 1983]].
The operational definition of stress is the score on the ten-question PSS. Other means of measuring stress are also possible [such as heart rate or blood pressure].
All of these have advantages and disadvantages.
Think 2.1 [Definitions] Define a ‘smoker.’
References
Cohen S, Kamarck T, Mermelstein R. A global measure of perceived stress. Journal of health and social behavior. 1983;385–96.
Fayet-Moore F, Peters V, McConnell A, Petocz P, Eldridge AL. Weekday snacking prevalence, frequency, and energy contribution have increased while foods consumed during snacking have shifted among Australian children and adolescents: 1995, 2007 and 2011–12 National Nutrition Surveys. Nutrition Journal. 2017;16[65]:1–4.
Levine RV. The pace of life. American Scientist. 1990;450–9.
McCrory P, Meeuwisse WH, Aubry M, Cantu B, Dvořák J, Echemendia RJ, et al. Consensus statement on concussion in sport: The 4th International Conference on Concussion in Sport held in Zurich, November 2012. British Journal of Sports Medicine [Internet]. British Association of Sport; Exercise Medicine; 2013;47[5]:250–8. Available from: //bjsm.bmj.com/content/47/5/250.
Meline T. Selecting studies for systematic review: Inclusion and exclusion criteria. Contemporary Issues in Communication Science and Disorders. 2006;33:21–7.
Raftery M, Kemp S, Patricios J, Makdissi M, Decq P. It is time to give concussion an operational definition: A 3-step process to diagnose [or rule out] concussion within 48 h of injury: World Rugby guideline. British Journal of Sports Medicine [Internet]. British Association of Sport; Exercise Medicine; 2016;50[11]:642–3. Available from: //bjsm.bmj.com/content/50/11/642.