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The IUP Journal of Computational Mathematics
Temporal Changes in the Parameters of Statistical Distribution of Journal Impact Factor
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The statistical distribution of Journal Impact Factor (JIF) is characteristically asymmetric and non-mesokurtic. Even the distribution of log10(JIF) exhibits conspicuous skewness and non-mesokurtocity. This paper estimates the parameters of Johnson SU distribution fitting to the log10(JIF) data for 10 years, 1999-2008, and studies the temporal variations in those estimated parameters. The 'over-the-samples stability' in the estimated parameters for each year is also studied by the method of resampling close to bootstrapping. It has been found that log10(JIF) is Pearson Type-IV distributed. Johnson SU distribution fits very well to the data and yields parameters stable over the samples. The paper concludes that Johnson SU distribution is the best choice to fit to the log10(JIF) data. It is also found that over the years the log10(JIF) distribution has become more skewed and leptokurtic, possibly suggesting the Matthew effect in operation, which means that more cited journals are cited even more over time.

 
 
 

The Journal Impact Factor (JIF) is one of the very important numerical measures of scientific or research importance of a journal. Notwithstanding the observations of Rossner et al. (2007), who question the veracity of JIF data altogether, the importance or quality of a paper/article (and, by implication, the author(s) of the paper/article) published in a journal is often judged by the JIF of the journal concerned. After the University Grants Commission, India, notified its Regulation on Minimum Qualifications for Appointment of Teachers and Other Academic Staff in Universities and Colleges and Measures for the Maintenance of Standards in Higher Education on September 23, 2009, JIF has become all the more important since publication of research papers/articles in high-impact journals has become an important factor in assessment of the academic performance of teachers in colleges and universities in India (Mishra, 2009). Impact factors are calculated every year for those journals that are indexed in Thomson Reuters' Journal Citation Reports.

In the past, researchers have hypothesized various types of statistical distributions underlying the generation mechanism of JIFs. These are: negative exponential (Brookes, 1970), combination of exponentials (Avramescu, 1979), Poisson (Brown, 1980), generalized inverse Gaussian-Poisson (Sichel, 1985; and Burrell and Fenton, 1993), lognormal (Matricciani, 1991; and Egghe and Rao, 1992), Weibull (Hurt and Budd, 1992; and Rousseau and West-Vlaanderen, 1993), gamma (Sahoo and Rao, 2006), negative binomial (Bensman, 2008), approximately normal (Stringer et al., 2008), normal (Egghe, 2009), generalized Waring (Irwin, 1975; Panaretos and Xekalaki, 1986; and Glänzel, 2009) and so on.

 
 
 

Computational Mathematics Journal, Statistical Distribution, Journal Impact Factor, Johnson System, Normal Distribution, Probability Density Function, Quantile Estimation Method, Computer Programs, Empirical Distribution, Universal Distribution, Burr and Dagum Distributions.