The semantic differential is a bipolar rating scale. It differs from the likert scale in that opposite statements of the dimension are placed at two ends of the scale and respondents are asked to indicate which they most agree with by placing a mark along the scale.
This has the advantage that there is no need for the scale points to be semantically identified. Any bias towards agreeing with a statement is avoided ,as both ends of the scale have to be considered.
The original development of this scale by osgood recommended the use of seven points on the response scale, and this number continues to be the favourite of researchers , although both five point scales and three point scales are used for particular purposes.With semantic differentials scales ,statement should be kept as short and precise as possible because of the need of the respondent to read and understand fully both ends of the scale. Attitudes can be difficult to express concisely, and it is sometimes difficult to find an opposite to ensure that the scale represents a linear progression from end to the other.
For these reasons semantic differential scales are usually better suited to descriptive dimensions. As with all self completion it is wise to provide a sample of how to complete the grid. Care must be taken that the two statements provided determine the dimension the researcher requires. The opposite of ‘modern’ might be ‘old-fashioned’ or might be ‘traditional’.The opposite of ‘sweet’ might be ‘savoury’ or ‘sour’ or ‘bitter’.This forces questionnaire writer to consider exactly what the dimension is that to be measured.This gives the semantic differential scale an advantage over the likert scale. Some dimensions may have no opposite other than a negative statement of attribute.