Parameters:
(1) number of citations in Year X to articles published in Year (X-1)
(2) total number of citable articles in Year (X-1)
(3) number of citations in Year X to articles published in Year (X-2)
(4) total number of citable articles in Year (X-2)
impact factor =
= ((number of citations to articles in X-1) + (number of citations to articles in X-2)) / ((number of citable articles in X-1) + (number of citable articles in X-2))
Interpretation:
• minimum impact factor: 0
• maximum impact factor: > 50
• The higher the impact factor the greater the journal's impact.
Limitations of impact factor (page 2):
• Negative citations count the same as positive.
• Lag time in publication of articles.
• The accuracy in counting citations at ISI (Institute for Scientific Information).
• Ease of access (an online publication may be more accessible and so more widely cited)
• Selection bias in the choice of journals and languages reviewed.
• Selection bias by publishers for articles of a certain type.
• Exertion of influence by editors.
• Citation by authors of their own work.
• Citations to "non-citable" articles in the journal.
• Review articles are cited more often than other kinds.
• Differences in citation behavior between subject areas.
