Different Anti dandruff shampoos contain different ingredients eg,
salic ylic acid, coal tar, zinc selenium, keta-conazole, etc.

I have a moderate but persistent dandruff problem. I have been trying
to get rid of dandruff for good but only with transitory success. I
have used many shampoos with different ingredients. They have some
effect but then the dandruff comes back.

How do I find out which ingredient (or which shampoo) is most
effective against MY TYPE of dandruff? By using them, I could not
determine their efficacy. Hence the question.

See a doctor and find out of betamethasone or Clobex are indicated.