pls .. I want to know if the impact factors of all journals are calculated in the same way .. that is to say .. it is right to compare between two journals on the basis of impact factors putted on their websites.
I had thought impact factors were calculated in the same way, hence allowing this comparison, but now that you've asked the question I am not sure and will check a library website, so if you just ask your librarian they should know
The calculation is done in the same way but it is only valid to compare the two journals if they are both in the same field of study.
For example a Q1 (top 25 journals in the field based on Thomson's Web of Knowledge listing) journal in Medicine like the New England Journal of Medicine has an IF=30 while a Q1 journal in Horticulture eg Euphytica has an IF=1.6.
Hence cross discipline journal IF comparisons are not valid.
Hope that answers your question Ayoub and Deborah.