Let's say, I used two scales that measures - 1. Perception of eco-label and 2. Perception of eco-brand. Each of them have 4 items (questions). Items are measured on 7 point-likert type questions. These scales have been previously used in other papers and their items were grouped under these 2 scales names with Factor Analysis in those papers as well. Therefore, According to previous papers, I know what item belongs to which scale.
My question is the following: Do I still need to do 2 separate Factor Analyses, in my paper, for grouping these items under 2 factors (perception of eco-label and eco-brand)? OR it is enough to know from previous papers which items belong to which scale?