i think some thing has been changed, suddenly from starting of april my organic traffic from google is dropped
Why google will disclose the algorithm changes ? I dont think we can figure out that when exactly and what changes are made in google algo, as a developer we can think that google may keep changing it slightly based on each day research and visitors requirements, as every day lot's of new keywords and new contents are being fed in Internet world.
Yup, but doing seo for site will not change enough, as the importance of all the SEO factors considered by google will be the same... Backlinks, Keyword relevance, Content quality etc...
This is very difficult to find out Google algorithm... We have to just follow the Google web master guidelines to achieve better result in search engines...
This year has only brought one major change that I know about. As of the beginning of this month load time has become a factor in rankings.