Traffic Reduced after Changing Preferred Domain

[ehealthaccess]

After 3 Years I have selected my preferred domain as www....com from that time my search engine traffic was reduced may I know the reason and is it for temporary problem or it will affect my site permanently.

Before I get 3000+ impress but now I am only getting 300 to 500 can anyone tell me what is the problem and how to solve it.

[aakk9999]

Could you provide a bit more information please.

Are you saying that you have selected www version of your domain as a prefered domain in Google Webmaster Tools and this is the only change you did?

If not, how did you change your preferred domain? Did you redirect from non-www to www version or something else?

When exactly did you do this change?

After the change, did you lose your traffic immediately or was it a slow drop over the time?

Have you analysed your traffic loss - is it across all pages/keywords or from a particular page /keyword set?