When assessing new therapeutic goods through clinical trials, researchers must obtain information on the degree of a patient’s physical response to therapy. This data then undergoes detailed statistical analyses in order to determine the safety and efficacy (effectiveness) of the drug or treatment.
Central to Clinuvel’s clinical trial design, and the value of these studies, is measurement of the severity of phototoxic reactions (adverse reactions to light or UV radiation) in trial patients. In order to do this accurately, a symptom severity scale has been developed based on the method of ‘Likert scaling’.
The Likert scale was initially conceived by an American psychologist and social scientist, Dr. Rensis Likert (1903-1981). In his research, Likert needed to measure and compare people’s attitudes or opinions in a way that was deemed scientifically sound. He aimed to generate a system that could convert psychological attitudes and beliefs into properties that could be measured on a true metric scale, as happens with metrics such as length and temperature. Likert did this by assigning quantitative values (numbers) to qualitative (the nature, description or quality of something) data so that it could be compared and analysed.
Characteristics of a Likert scale:
- The scale must have a construct, which is the attitude or feeling being measured. In this case, it is the extent of the phototoxic reaction as perceived by the patient.
- The options listed on the scale need to be valid, undimensional (all measuring the same trait) and discriminating; so that distinctions can be made between them.
- The scale contains several options for the respondent to choose from.
- Options are arranged according to rule; this means that they are in order of level, ranging from one extreme to the other, with the intermediate responses listed in between.
- Options are labelled with consecutive numbers.
- Options are accompanied by written descriptions which denote evenly spaced graduations.
- Strictly speaking, a Likert scale consists of several questions or statements (called ‘items’) which the respondent must answer. In this respect, the symptom severity scale is a single item rather than a traditional Likert scale.
The following is a sample of an 11-point ‘symptom severity scale’, similar to that used in Clinuvel’s erythropoietic protoporphyria (EPP) clinical trial (CUV017). The patient is asked to indicate the number of phototoxic reactions in a given period of time and the maximum severity of each reaction is reported according to the following definitions:
0 None - No symptoms.
1-3 Mild - The reaction is transient and easily tolerated, not requiring any treatment.
4-6 Moderate - The reaction caused discomfort and interrupted usual activities. Some form of
treatment was required.
7-9 Severe - The reaction caused considerable interference with usual activities and may have
been incapacitating, requiring treatment.
10 Worst Imaginable – The reaction causes extensive interference with usual activities and is
incapacitating, requiring strong analgesics and/or hospitalisation.
Using a scale like this one means that numbers that can be meaningfully assigned to a person’s estimation of their physical symptoms. It allows for standardisation of a variable, ‘symptom severity’, which is highly subjective. This creates uniform levels which can be effectively used for statistical analysis.
References
Trochim, W.M.K, 2006, General Issues in Scaling, The Research Methods Knowledge Base, 2nd edn, retrieved 10th August 2010, <http://www.socialresearchmethods.net/kb/scalgen.php>.
Uebersax, J.S, 2006, Likert scales: dispelling the confusion, John Uebersax Enterprises LLC, retrieved 10th August 2010, <http://www.john-uebersax.com/stat/likert.htm>.
Image reference
‘69/365 – food diary.’ uploaded to flickr.com by ‘BLW Photography’ on the 18 November 2009, <http://www.flickr.com/photos/macbeck/4123122634/>.
