What is the difference between SCI and SCIE?
Thomson Reuters customer support explanation on SCI and SCIE:.
The Science Citation Index (SCI) is a sub-set of the Science Citation Index Expanded (SCIE), containing journals that rank competitively among the most highly-cited core journals in their category or categories. The Science Citation Index Expanded is essentially the web version of what used to be a database available only on CDRom/Diskette.
When selecting the journals for the Science Citation Index we choose the top journals from each subject category and supplement this with top regional journals from each category to give broad geographic and multidisciplinary coverage. The evaluation of and acceptance of a journal for the Science Citation Index Expanded or the Science Citation Index is essentially the same with one major difference.
This difference is in the application of citation analysis to the journal. While every science journal in our database is covered in the Science Citation Index Expanded and only those journals of relatively significantly higher citation impact are selected for the Science Citation Index. In other words, Science Citation Index covers only the most highly cited, highest impact journals in each category. This is because of the constraints of the CDROM and print media there is no difference in the selection process for Science Citation Index and Science Citation Index Expanded journals.
From Thomson Reuters:
... the evaluation of and acceptance of a journal for the SCI or the SCIE is essentially the same with ONE major difference. The only difference is the storage media. SCI is only available on CD/DVD format; however, SCIE is available online.
I got an explanation from Clarivate Analytics:
Based on the fact that Thomson Reuters selects journals of SCIE (including SCI) through a strict selection process, we hereby prove that journals of Science Citation Index® (SCI) and Science Citation Index ExpandedTM (SCIE) have the SAME QUALITY as the journal selection process for journals of SCI and SCIE is essentially identical.
The only small difference between of Science Citation Index® (SCI) and Science Citation Index ExpandedTM (SCIE) is the storage format. As known, both SCI and SCIE are available online. However, SCI is available on CD/DVD format but SCIE is not.