| Abstrakt: |
The British number plate test and the Snellen test of visual acuity are compared. The observations of 60 subjects, 30 of whom have failed the official number plate test, are analysed statistically. It is found possible to estimate the probability of a subject having a specified Snellen acuity, reading a number plate of the 3⅛" (80 mm) symbol type, at 67 ft. (∼ 20.5m). It is considered, however, that the probability of passing the official number plate test is a different value and this is also shown to be estimated from the Snellen visual acuity. The calculations based on the sample of candidates who had failed the number plate test suggest that a driving test candidate with a Snellen decimal acuity of 0.55, or approximately 6/12[SUP+2] in clinical notation, has a 50% chance of passing the number plate test, but the level of visual acuity which would fail the same number of candidates as the number plate test is deduced from an approximate population model, to be 0.6, or 6/9[SUP-2]. Many other quantitative estimates relating the two tests are given in the text and accompanying tables and figures. [ABSTRACT FROM AUTHOR] |
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