More effective for surveys: horizontal Likert scale or answer options listed vertically?

Question

My survey has numerous questions with answers ranging from, for example, 'Not at all satisfied' to 'Extremely satisfied' and 'Not important' to 'Very important'.

My instinct is to display these answer options in 5-point horizontal Likert scales with a label on each endpoint and a label on the middle-point; A friend thinks that displaying the answers spelled out individually and displayed vertically (example below) may result in people more quickly and easily understanding the answer options, and more accurately answering questions.

Do people more quickly and easily understand answer options when they are spelled out individually, and what effect does displaying answers that way have on the accuracy of answers?

Example of answers spelled out individually and displayed vertically:

A) Not at all satisfied
B) Slightly satisfied
C) Moderately satisfied
D) Very satisfied
E) Extremely satisfied

Answer 1

Yup, people more easily understand answer options when they're explicitly spelled out. It also helps to ensure that everyone choosing the option is doing so with the same understanding, as explained in this "wording for rating scales" PDF):

Providing a word label over each point better ensures that everyone interprets the points similarly reducing measurement error.

If everyone has the same understanding of the option, that should increase the accuracy of the answers.

Here are some other examples of phrasing for Likert ranges:

• http://researchbasics.education.uconn.edu/likert_scales/
• https://www.surveylegend.com/likert-type-scale-responses-examples-with-examples/