In addition, invariance of classification is essential to measurement in a two-way frame of reference, such as in comparative judgement (Andrich, 1988).
Jones and Alcock (2014) asserted that the larger number of judges in comparative judgement can be more costly than analytical marking, but this is offset by the greater reliability in the comparative judgment process.
The issue of time in making comparative judgements was highlighted in a study by McMahon and Jones (2014), who investigated the use of comparative judgement in the assessment of a secondary school chemistry experiment.
One of the main reasons for high reliability of relative comparative judgements compared to absolute analytical judgements is that, relative judgements require larger numbers of judges.
For example, a study investigating absolute and relative judgements and standard-setting by Gill and Bramley (2013) considered the accuracy of holistic comparative judgements in relation to the original analytical marks of examination scripts that were 'close together in overall mark' in a standard-setting exercise.
Multivariate analyses using General Linear Models, GLM, revealed gender differences in comparative risk judgements for gum disease, whereas social position varied systematically with risk judgements for tooth decay, gum disease and air pollution.
During this study Professor Richard Kimbell from London University was a visiting scholar at the centre; he introduced the e-scape project, assessing complex practical performance using evidence collected in digital forms, and the use of comparative judgements for generating scores (Kimbell, 2012).
Absence of unrealistic optimism in comparative risk judgements for cancer has been documented elsewhere [ 2].
This study adds to existing evidence by indicating the presence of optimistic biases in comparative risk judgements for various oral health hazards among young adults from the general population.
A sizeable literature has confirmed optimism in comparative risk judgements with respect to various health and safety risks, ranging from catching a cold to having AIDS and experiencing an accident [ 4- 7].
