Hi Tayeb,

I am not sure is this will answer your question, but I am currently designing an online survey using the Likert scale. Like you, I was wondering about the rationalizations for or against 4, 5, 6, or 7 point scales.   I have not found anything definitive, but there are two articles that could possibly  help you. The first article focuses on comparing the impact of different  Likert scales on the data collected.

Leung, S. (2011). A comparison of psychometric properties and normality in 4-, 5-, 6-, and 11-point likert scales. Journal of Social Service Research, 37(4), 412-421. doi:10.1080/01488376.2011.580697

http://journals1.scholarsportal.info.proxy.library.carleton.ca/pdf/01488376/v37i0004/412_acoppa56a1ls.xml

This next article may also be of interest.  It focuses more on the structure of the Likert scale test, namely on the directionality of the questions in the questionnaire.

Maeda, H. (2015). Response option configuration of online administered likert scales. International Journal of Social Research Methodology, 18(1), 15-26. doi:10.1080/13645579.2014.885159

http://journals1.scholarsportal.info.proxy.library.carleton.ca/pdf/13645579/v18i0001/15_rocooals.xml

I hope these articles help.

http://journals1.scholarsportal.info.proxy.library.carleton.ca/pdf/01488376/v37i0004/412_acoppa56a1ls.xml

http://journals1.scholarsportal.info.proxy.library.carleton.ca/pdf/13645579/v18i0001/15_rocooals.xml

thank you very much Mr. Don Myles for your interest and your answer. I have sent an article to a journal  named (Jordan Journal of Business Administration), one of two reviewers asked me to provide a justification for the use of the seven-point scale in my article. when I look for the reason in my modest readings, I found no convincing answers to his request. but what I find is to review my references, I have told him that among nearly 30 articles there are almost seven articles in referred  journals have used a seven-point scale. the second argument that the seven-point scale is a mediate scale in length comparing to 5 or 9 point scales.

what do you think Mr. Myles about this answer? 

i can send you the reports of reviewing but in Arabic.

Hi Tayeb,

Unfortunately, I do not read Arabic. Both of your arguments are good and I am not sure what the reviewer is looking for,.  You could possibly use these two citations to support your use of a seven-point scale, however,  I am not well versed in this area.  I hope these help you. 

Dornyei (2003, pp. 37-38) states,

“Original Likert scales contained five response options (as just illustrated), but subsequent research has also used two-, three-, four-, six-, and seven-response options successfully. The most common step numbers have been five or six, which raises a second important questions: Shall we use an even or an odd number of steps?      Some researchers prefer using an even number of response options because of the concern that certain respondents might use the middle category ('neither agree nor disagree, ' 'not sure, ' or 'neutral') to avoid making a real choice, that is, to take the easy way out. Although according to research, this may be true of roughly 20% of the respondents, it appears that the inclusion or exclusion of a middle category does not affect the relative proportions of those actually expressing opinions and thus does not modify the results significantly (Nunnally, 1978; Robson, 1993).”

You could also look at Joshi, Kale, Chandel, and Pal (2015, p. 398).  They state that a scale larger than 5 offers the participant the ability to select the best fitting choice and not simply the closest one to their real opinion.

“Seven /ten point scale - They are the variation of 5 point scale in which adjacent options are less radically different(or more gradually different) from each other as compare to a 5 point scale. This larger (step by step) spectrum of choices offers more independence to a participant to pick the ‘exact’ one (which he prefers most) rather than to pick some ‘nearby’ or ‘close’ option [15].”

Dörnyei, Z. (2003). Questionnaires in second language research: Construction, administration, and processing. Mahwah, N.J: Lawrence Erlbaum Associates.

Joshi, A., Kale, S., Chandel, S., & Pal, D. K. (2015). Likert scale: Explored and explained. British Journal of Applied Science & Technology, 7(4), 396-403. doi:10.9734/BJAST/2015/14975

Mr. Myles I have attempted to reach this articles in databases (JSTOR, SCIENCEDIRECT, SPRINGER) but these journals are not indexed in their lists.

but in the net, I have found a Brazilian article (of course in English). we can read it in this attached file below. 

thank u for your intereset.

best regards.

thank u again Mr. Myles

I am so grateful to u professor.