The Farnsworth-Munsell (F-M) 100 hue test1
is widely used for measuring chromatic discrimination by clinicians and vision scientists. As well as helping to identify various congenital colour vision deficiencies, it is a useful and sensitive test for measuring the changes due to neuronal disease2,3
or possible side effects in therapeutic management.4,5
The test was first devised by Farnsworth in 1943 and the present 85 coloured cap version dates from 1957. The caps are arranged in four boxes, each containing a fixed anchor cap at each end. There are 22 caps in the box 1 and 21 caps in each of remaining three boxes. The total error score (TES) is a measure of accuracy of an observer in arranging the caps so as to form a gradual transition in chroma between the two anchor caps; the higher the number of misplacements the larger the TES. TES norms for the test have been published at intervals including those by Verriest et al6–8
based on data for observers divided into various age cohorts (either 5 year or 10 year).
There is, however, ambiguity about scoring cap misplacements occurring near the ends of boxes in the published norms. The test instructions for scoring do not specify how to account for chromatic step changes across the boundaries between boxes. Before automatic scoring equipment was developed, most testers scored the test on the basis that the anchor caps at the ends of the boxes did not exist. Thus a sequence such as cap numbers 20, 19 in the first box followed by caps 26, 23 in the second box would have a partial error score for the last arranged cap in the first box (19) calculated by adding |19 − 20| to |19 − 26| and then subtracting 2 (that is, 1 + 7 −2 = 6). Likewise the partial error score for the first arranged cap in the second box (26) would be |26 − 19| + |26 − 23| − 2 = 8. For this method, the total error score from summing all the partial scores is a multiple of four. Since the introduction of automatic scoring, testers have scored the caps in each box independently of the caps in the previous or following boxes by making use of the numbers of the anchor caps. With this method, the total error score is not necessarily a multiple of four and can result in a lower TES than that obtained using the former method. The scoring artefacts associated with the division of the test into boxes have been addressed by Victor9
and by Craven,10
the latter drawing attention to the point that box-end caps have lower scores than mid-box caps when the TES is low but higher scores when the TES is high.
A further scoring anomaly arose with earlier versions of the test when the boxes were shorter than the current versions. Some testers removed cap 85 from the first box and installed it as the anchor cap instead of 84, leaving just 21 caps for observers to arrange. For example, Verriest et al
observers used binocular vision and the scoring disregarded the numbers of the anchor caps whereas his later observers8
were tested both binocularly and monocularly, the scoring excluded cap 85, and the numbers of the anchor caps were used for calculating misplacements at the ends of boxes.
Finally, the distribution of TES at a given age group has a skewed distribution, hence it has been recommended that the transformation of TES to the square root of TES (√TES) provides a nearer normal distribution for statistical analysis of the data.11
Although this recommendation has been questioned,12
more recent normative data have been published as means of √TES for 5 year and 10 year age groups.8,13
More statistically efficient methods based on maximum-likelihood procedures have been offered by Craven14,15
but they are not convenient to use in a clinical situation.
Here, we report normative data for observers in each year of age from 5 to 22 and for 10 year age groups from the 30s to the 70s in both TES and √TES form. We also report partial error scores (TPES) for the red-green and blue-yellow axes of colour vision deficiencies because they represent a useful way of studying the relative contributions of ageing and retinal disease on colour discrimination. We have, therefore, outlined TPES scores as well as a comparison of the means from using the two methods of scoring misplacements at the ends of boxes.