[Statistics (III) Apples plus pears; level of measurement].

: A score is a numerical expression of an observation, such as length or number in rank ordered scores. Scores may be manipulated. A mean score 8 for arithmetics represents an indication of the achievement, but the mean score 1.5 for 'belief' (from 1 Roman Catholic, 2 Anglican and 3 = not religious) is meaningless, due to the so called 'level of measurement'. In relation to the measurement scales, measures of central tendency and deviations thereof, among which the standard deviation, are presented.