Communication Journals
Just what really is a Communication Journal? It sort of depends on who's counting. But it does matter when issues of academic productivity, university and disciplinary stature, and the current National Research Council's national ranking procedures are considered.

These are the Communication journals that appeared in both The Iowa Guide (1998) and Thomson Scientific/Institute for Scientific Information's (ISI) Journal Citation Reports (1997). Three others that are included on only one of the lists were added as being clearly communication journals, as of 1997/1998.

I have not collated the overlap list using the most recent edition of the Iowa Guide. However, the full list of ISI Communication Journals for 2006 follows. These are used, along with the Sociology and Psychology journals, as the basis for the National Research Council productivity compilations for the Social and Behavioral Sciences (thanks to Charles Atkin at MSU):

Alternatively, here's a list of journals typically considered Communication journals, with an indication of whether they are included in the ISI database or not (as of March 2007) (thanks to Linda Putnam at Texas A&M). Some of these have actually been included in ISI in prior years, but have been dropped for a variety of reasons. There are likely other titles that would or should be considered as Communication journals.

So there are different lists of "Communication Journals" depending on who collects the information and what's considered "communication." However, the ISI's Social Science Citation Index (the basis for the social science Web of Science), and particularly the Core Communication Journal list in its annual Journal Citation Report, are currently the primary bases for computing citing totals, cited totals, impact factor, citation half-life, immediacy, and other measures. As you can see from above, what a flexible take on communication journals might come up with is somewhat different from what Thomson/ISI comes up with. So how are journals selected for inclusion?

Criteria for ISI Selection (summarized from The Thomson Scientific Journal Selection Process, January 2004, and from Linda Putnam)
ISI indexes and collects bibliographic, abstract and cited references data for over 8,700 journals worldwide (and over 7,000 books and proceedings) in the sciences, social sciences and arts and humanities. They do not index every journal, as research shows that most (85%) published and cited (95%) articles are included in a core of about 2,000 journals. Thus they accept only about 10-12% of the 2,000 new journal titles evaluated annually. And journals already indexed that fail to continue meet the criteria may be dropped.

The criteria for selection of ISI are both quantitative and qualitative. However, ISI relies heavily on impact factors. The evaluation of the journal will begin when at least three consecutively published, on-time issues are received along with a formal request for consideration letter. Evaluation typically takes a full year with issues being sent on a regular basis. Criteria for selection include:

a. Timeliness - publish on time, not chronically late.
b. Adheres to international editorial conventions-informative titles, published in multiple languages, use of author keyword, abstracts for articles, etc.
c. Use of peer review process - completeness of cited references.
d. Editorial content - journals that publish emerging topics or new areas are given special consideration.
e. International Diversity - covers international topics, includes international editorial board, publishes authors based internationally.
f. Citation Data - overall citation rate, impact factor, and immediacy index. ISI folks consider the publishing record of the journal's authors and the editorial board members, noting where articles have been published and if their work has been cited. It also examines citations from its own ISI database. So the calculations are based on being cited in the journals currently included in ISI.
g. E-journals must meet the same criteria for evaluation.
h. ISI's www.isinet.com

As of March, 2007, ISI just accepted Management Communication Quarterly into its Communication database, and is currently reviewing three journals: Journalism History, Text and Performance Quarterly, and Asian Journal of Communication. New Media & Society was added a few years ago.

Impact Ratings Based on Articles Published and Articles Cited
Impact Ratings are the ratio of number of citations received to articles in that journal, divided by number articles published in that journal two years prior. For example, in 2005, the Journal of Communication had an impact factor of 1.134. This was based on the number of citations to articles published in JoC in 2003 (61) and 2004 (32), or 93, and the number of articles published in JoC in 2004 (39) and 2003 (43), or 82. 93/82=1.134. Cited Half-Life is the number of years it takes for half of all the citations to articles in that journal to have been received.

In general, there is an extensive literature on the uses, meanings, and problems of citation datae. The October 14, 2005 issue of the Chronicle of Higher Education contained a report on the uses and abuses of impact factors. Thomson Scientific (http://www.thomson.com/solutions/scientific/scientific.jsp, April 2005) cautions against using citation data without qualifications. Citations are influenced by a variety of factors, including "language, journal history and format, publication schedule, and subject specialty." Impact ratings change noticeably across years. Articles considered for counting citations do not include editorials, letters, news items and meeting abstracts. Published articles are coded by document type, but their citations are not, so you can't tell if citations are to letters, reviews, or original research (although only review and original research articles are used in computing impact factors). Journals may change their size; for example a journal that expands from four to six issues will typically have substantially lower impact the following year, as citations tend to increase in the second year, but the number of articles used in the impact denominator in the first year are already higher. It takes two years after a journal changes its title for the journal data to be fully allocated to the new title. Again, the impact factor may be lower for the new title, and higher for the old title, during the transition. Finally, some journals are not indexed as source journals (for a variety of reasons), so only citations to them are totalled in the JCR. Such cited-only journals do not include self-citations, again reducing their impact factor.

Ranking of Communication Journals by Impact Rating, 1998-2002 (thanks to Sam Luna at ICA)

Impact Ratings and Cited Half-Life of Communication Journals, 2000

Impact Ratings of ICA Journals, 2000-2005 (summarized from Thomson Scientific web pages)

You can see that the three ICA journals have generally been increasing their impact ratings, especially compared to 2000. Paradoxically, in order to get higher impact ratings, a journal has to be (a) included in the ISI indexing database, (b) included in the JCR Core Communication Journal listing, and (c) receive sufficient citations from other journals already included in the ISI database. So current and new journals aspiring to be included in the ISI database - and thus become in some ways official communication journals -- have considerable challenges!