The ISO 20282 test methods for everyday products include primary product goal setting, specification
of tasks to be performed in a given environment and measurements to reach the goal. For this standard, the
method suggests selecting user groups that reflect the intended user groups; if the task should be easy for
the general public to handle, the product should be tested by individuals with special requirements.32 For
products with low complexity, effectiveness is the most important evaluation factor. Satisfaction can be
graded using a five-point smiley scale,33 which is likely to be interpreted in the same way across different
cultures. In some cultures, 1 represents the highest grade, while 5 is the highest grade in other cultures. In
the German customer satisfaction barometer, the highest satisfaction score a company could receive was
1, while 10 was the highest grade in the Swedish equivalent. The main disadvantage of the smiley scale is
that it does not lend itself to statistical analysis unless it is assumed that there is an equal space between all
levels. Also, all interval scales are usually heavily skewed in one direction, particularly scales with fewer
scale steps; in other words, a five-point scale is more skewed than a seven-point scale. The only way to
remedy this problem is to add more respondents to the tests.