Agree Disagree scales are one of the most common types of question found in social research surveys. They are usually used to ascertain the opinions and perceptions of respondents relating to a particular issue. However, research suggests that framing questions in this way results in a notably lower level of quality (read: accuracy) in responses [1].
When referring to Agree Disagree (A/D) scales, the following is how it would typically be framed/presented (obviously this is an example of self completion format, alterations to wording and structure would be expected for telephone surveys). This type of question is sometimes referred to as a Likert scale, after Rensis Likert who developed it in 1932:

 

Framing a question in this way has a number of limitations that need to be considered:
  • The statements themselves are more often than not leading, such as “I never read the flyers I receive in my letterbox”.
  • Acquiescence response bias needs to be considered. This is the phenomenon whereby some people will agree with almost anything; due to being an agreeable person, assuming that the researcher agrees so they defer to their judgement, and/or because agreeing takes less effort than rationalising disagreement. [1].
  • Social desirability bias also needs to be considered, whereby respondents will answer in a way that places them in a more favorable light to others. The risk of this is greater when using direct contact surveying methodologies such as face-to-face or telephone.
  • Some people will shy away from the extreme ends of a rating scale, particularly if it is a sensitive issue, which can result in central tendency bias.
It is instead suggested that one employes an item-specific (IS) response scale structure. For instance, instead of asking for level of agreement with the statement “I never read the flyers I receive in my letterbox” you instead ask “How often you read the flyers you receive in your letterbox?” with a scale such as ‘Always, Sometimes, Rarely, Never’. Or you could explore the issue in much more depth, having a series of questions to draw out if there are variations between types of flyers, and ascertain greater detail about actions, such as read and discard, read and share with friends/family, read and pin on fridge/pin-up board etc.
Whilst this approach will clearly provide more useful detail, and avoids the risk of A/D scale biases, it does reduce the opportunity for comparison across multiple statements to identify underlying phenomenon. It also requires greater levels of concentration from the respondent to think through each scale individually. This later consideration, however, can in some cases be a good thing as it will encourage greater levels of engagement with the survey (that is, minimise the risk of the respondent ‘zoning out’). Adopting a IS approach can also significantly lengthen survey duration (impacting on respondent satisfaction, response rates and costs).

Conclusion:

As with the design of any survey question, you need to decide on the best approach based on a wide variety of considerations. For some research, A/D scales may be appropriate, yet for others it may be wise to avoid them.The primary consideration should be how you are going to use the information/what type of information is going to be most useful to you. Cost is also a consideration (presenting a number of statements in a A/D table is cheaper than IS questions), however, cost should never overrule usefulness – if you are going to conduct a survey that is not usefull or is likely to provide sub-standard results just to save money, it is better to not run the survey at all.
If you are going to use Agree Disagree Scales, things to consider are as follows:
  • Always randomise the list of statements to avoid response bias.
  • Keep the list of statements to less than 10 to minimise the risk of response fatigue.
  • The benefit of using a Likert scale is that it allows for identifying of variations which might point to an underlying phenomenon relating to the topic being explored.

References

[1] Saris, W.E et al (2010),  Comparing Questions with Agree/Disagree Response Options to Questions with Construct-Specific Response Options, Survey Research Methods, Vol 4 No1 p61-79.