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For gathering users' emotional reactions to web pages via a survey, a researcher could use either a Likert scale (e.g., Agree Strongly - Agree Somewhat - Indifferent - Disagree Somewhat - Disagree Strongly) or a semantic differential, (e.g., Love - Like - Indifferent - Dislike - Hate). Please note: I'm not talking about doing a usability test; this is about attitude surveys.

Why would a user researcher choose Likert instead of Semantic Differential or visa-versa?

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Semantic differential scale (SDS)

To begin with, your example of SDS is incorrect (Love - Like - Indifferent - Dislike - Hate). Essentially, you have amplified a key challenge in differential scales - coming up with a dichotomous pair.

SDS pairs

A SDS is based on a dichotomous (bi-polar) pair of adjectives. For example:

Simple O O O O O Complex

Finding pairs may not be easy. For instance, what is the opposite of boring? fun or exciting?

Likert can do things SDS can't

Also, sometimes it is hard to find pairs to articulate exactly what you wish to ask. How do you convert this likert to SDS:

I would recommend the site to friends:

O Strongly Agree

O Agree

O Neutral

O Disagree

O Strongly Disagree

How many questions?

One advantage of SDS is that there is typically one question (eg, How would you rate the site) to which there are a few scales each involves only a pair of words. So there's less to read.

With likert, each scale is the same, but each has a different question - so more to read.

Likert scale is easier to answer

The consistency of the likery scale (same for all questions) makes them somewhat easier to answer. This is in contrast to the dual terms that change between each scale on SDS, which not only leaves the adjectives prone to subjective interpretation, but also requires people to consider a pair of adjectives instead of simple agree/disagree variations.

SDS scale is a split scale

Both scales essentially ask for intensity judgement, but SDS is split in the middle where likert isn't. A person filling and SDS scale will typically follow 2 steps:

  • Is it good or bad? (one side or the other). If you do provide a neutral option, this is also an option.
  • How good or bad is it?

Note that on a SDS with 5 points, you only have 2 intensities per side (thus SDSs are often 7-points, so there are 3 intensities per side; but that in itself makes the scale harder to answer as people find it harder to discriminate between the options).

With a 5 point likert there are 5 intensities to choose from. Although you can argue that the middle point splits the scale to good and bad, the fact there aren't two polars mean it ain't quite so. Consider:

I think the site looks professional. (Answer: Disagree).

The person disagrees that the site looks professional, but they may not think it looks amateur - on a SDS scale, they may still mark the middle point.

Consider the following dialog:

- Do you think David Cameron is a good prime minister?
- No I don't.
- Is he a bad one?
- I didn't say so, he isn't bad, but he isn't good.

Summary - it depends

So again, it depends on what exactly you are trying to find out. Mind you that there are other strategies you may wish to consider (BERT, for instance), and many other variants that may play a part.

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