The most simple pain assessment scale is the Visual Analogue Scale (VAS). The reliability and vality of this scale has been published and it has been used in a lot of studies and populations.
These two studies might help you
Article Int Reliability and validity of the visual analogue scale fo...
Article Analysis of outcome measures for persons with patellofemoral...
Pain is a subjective experience, whatever type of scale you will be using will only highlight to the care provider the amount of pain the person is having. In my experience, it does not matter what type of scale you will be using, just ask your patient what he/she favours. Go for the simples one, the descriptive as many can understand it. Some feels it difficult to put their pain into numbers but it work very well with oncology cases especially the young age adults.
I recommend Numerical Rating Scale.this is very easy to measure pain and a very well validated tool.you can convert this to rupee scale to make it simple.