I want to use three established scales which have a Likert Scale as a response - for instance the 10-item Need for Belonging scale (Leary et al., 2013). This scale is a 1-5 response alongside another scale and the third scale is a 1-7 response. I would like to ask that when a participant answers the scales, can I compute a mean score from their answers and thus have a per participant score like this for each scale i.e. three scores, one for each scale per participant? Some papers I read that employ these scales say "To analyze the motivational scales, mean scores were computed across the relevant items to form indices" or "We averaged the items in each scale and used the average scores in the data analyses." but I was not sure how to interpret them.
Comment continued: Also, if your analysis will involve any comparison of Likert-5 data with Likert-7 data, you may need to transform Likert-7 for compatibility with Likert-5. Maybe something like $L.5 = 2(L.7 - 4)/3 + 3 = 2L.7/3 + 1/3$ might work.
Consider Likert-7 data:
L.7 = sample(1:7, 100, rep=T) summary(L.7) Min. 1st Qu. Median Mean 3rd Qu. Max. 1.00 2.00 4.00 4.05 6.00 7.00
'Transformed' to L.5 scale:
L.5 = 2*L.7/3 + 1/3 summary(L.5) Min. 1st Qu. Median Mean 3rd Qu. Max. 1.000 1.667 3.000 3.033 4.333 5.000
Note: There is more than one way to do this. You can google something like 'transform Likert 7 to Likert 5' to see links with lots of approaches and lots of ads.