using the academic motivation scale (AMS C-28)

To calculate a person's score on the AMS, you need to find the mean (average) response for each of the subscales. These means will vary between 1 and 7. You then insert these means in the following formula which will enable you to calculate a self-determination index. 

2((know+acc+stim/3))+iden-((intro+reg/2)+2amo)=self-determination index

know=intrinsic motivation to know

acc=intrinsic motivation to accomplishments

stim=intrinsic motivation to experience stimulation

iden=identification

intro=introjected regulation

reg=external regulation

amo=amotivation

The highest level of self-determination: 2((7+7+7/3))+7 - ((1+1/2)+2*1)

The highest self-determination score = +18:

2((7+7+7/3))+7 - ((1+1/2)+2(1)

2((21/3))+7 - ((2/2)+2(1)

2((7))=& - ((1)+(2)

2((7))+7 - (3)

2((7))+7 - (3)

14+7-3=18

This formula can be put into an Excel spreadsheet, and the survey instrument results can be plugged in to calculate survey respondent's self-determination scores.

The formula in the scoring guide will give you scores ranging from -18 (a very low self-determination score) to +18 (a very high self-determination score). Most of the people tested with this scale have scores around +10. The closer the score is to +18, the higher self-determination a person has. The closer the score is to -18, the lower self-determination a person has.  Scores will be relevant within the group tested. In my study, testing college students motivation and comparing two groups, scores ranged from -3 to +11. 

I would like to mention that this scale has not been normalized. This index is only used for research purposes. Nevertheless, we noticed that a high (self-determination) index is associated with positive consequenses and, on the opposite, a low (self-determination) index is associated with negative consequenses for the person. (personal correspondence 2015-04-21 21:37 GMT-04:00 Bob Vallerand)