Citations in Psychology PhD Theses: An Obsolescence Study
Obsolescence studies are one of the main areas of bibliometrics and infometrics. Obsolescence is a vital aspect of scientific literature. Growth and obsolescence are usually considered together, because they represent the initial and final stages of the information cycle. Growth studies investigate patterns in the creation of literature over time.
An obsolescence study could be treated as an aspect of citation analysis for journal articles. Obsolescence studies are useful for researchers, librarians, and decision-makers in information centers. They are also helpful for pioneers in a scientific discipline to know how far they must go back to obtain material in their field of interest.
The present study attempts to discover the obsolescence rate of psychology literature cited in the doctoral theses awarded from 1963 to 2005, at S.V. University, Tirupati, Osmania University, Hyderabad, and Andhra University, Visakhapattanam. The study focuses on the citations included in doctoral theses awarded in psychology.
The objectives of the present study are to discover:
The objectives of the present study are to discover:
Material and Methods
The doctoral theses which are the products of research activity were examined for the study: 141 theses in psychology, accepted between 1963-2005 by Sri Venkateswara University,Tirupati, Osmania University, Hyderabad, and Andhra University, Visakhapattanam. The total number of journal and book citations found in those theses is 14,374 and 7,110.
The analysis of different characteristics of the literature was carried out on the citations. Number of authors, bibliographic format, year of publication, journal name, subject, country, language, and publisher's name were recorded.
The data was analyzed using Microsoft Excel and the Statistical Package for the Social Sciences (SPSS).
Review of Literature
Obsolescence is defined as the decline over time in the validity or utility of information. Studies of aging or obsolescence of documents commonly assess the decline in the use of a representative set of documents over time. Growth in the literature of a particular field plays an important role in age distribution.
Such studies help librarians decide which documents to keep or discard. To compare the speed of decay in different subjects, “half-life” is used as a measure. Half-life refers to the time during which one half of the current active literature was published.
The study of age of literature basing on citations has a long history. The age of the literature has been analysed in physics (Hooker 1935), speech literature (Brodus 1953), physiology (Lowler 1963), sociology (Lin and Nelson 1969), English literature (Heinzkill 1980), and mathematics (Line 1972). Other studies include chemistry (Brown 1980, Aruna 1999), biological sciences (Vimala 1997), and geology (Mahapatra and Bhagavan 2000).
Results and Discussion
Table 1 presents the obsolescence rate of literature in psychology.
Table: 1: Citation frequency of journals and books in psychology
More than one-quarter of journal citations are 8 years old or less. Fifty percent of journal citations are 14 years old or less. About 75 percent are 22 years old or less.
More than one quarter of book citations are 11 years old or less, slightly over half are 19 years old or less, and. Seventy five percent are 28 years old or less.
Age Distribution of Book and Journal Citations
The Kolmogorov-Smirnov (K-S) test was used to test the exponentiality of the distribution. The Observed (F(x)) and Estimated (E(x)) cumulative percentages and the absolute differences between the observed and estimated cumulative percentages were calculated.
[D N = [1F(x)-E(x)1] are calculated and are shown in Figures 1 and 2.
Under the assumption that the data follow a negative exponential distribution, the estimated cumulative percentages are calculated using the formula of exponential distribution
E(X) =1-e d x
Where d =1/mean and X = 0, 1, 2, 3… n
Significance at 0.01 levels: The K-S statistic (the critical value of D) is equal to 1.63/n 0.5. In this case n= 252 and hence the critical value of D from table it is observed that the maximum value of D does not exceed this critical value (0.0129) and hence it confirms statistically that the age distribution of citations in both bibliographic forms viz., journals and books, follows a negative exponential distribution in all the fields under study.
Half-Life of Journal Citations
A graph is plotted taking the age of citations (in years) on X-axis and cumulative percentage of citations on Y-axis to find out half-life of citations. A line parallel to the X-axis is drawn from a point say "A" representing the half of the citations to meet the curve say "B". Then perpendicular to X-axis (BC) is drawn from point B to meet the X-axis at C. "C" represents the half-life period of citations.
The half-life value obtained by Brown (1980) for chemical Literature is 9.3 years. Vimala (1997) obtained a half-life value of 16.22 years for biological sciences. Aruna Prasad Reddy (1999) obtained a half-life value of 17.84 years for chemistry and Mahapatra and Bhagavan Das (2000) obtained a half-life value of 17 years for geography. In general literature relating to descriptive aspects like properties of matter, basic methodology etc., basic laws and basic concepts decline more slowly compared to empirical matter. The above figures indicate that the obsolescence rate differs from one subject to another and also from one bibliographic form to another one. It is noticed that the half-life period is longer for books than for journals.
Figure 1. Citation frequency of journals in psychology
Figure 2. Citation frequency of books in psychology
Findings and Conclusion
Obsolescence studies play a vital role for librarians, researchers, and information managers as a decision support tool for the retention of the most frequently-used literature, and is also useful for weeding out unused or less-used literature.
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BRODUS (R N).The research literature of the field of speech. Chicago, ACRL (ACRL monograph no.7) 1953.
LOWLER (E). Physiology of the scientists: Age and authorship of citations in selected physiological journals. Physiological Reports. 13; 1963; 537.
LIN (N) and NELSON (C E). Bibliographic reference pattern in core Sociological journals, 1965-66. American Sociology. 4; 1969; 47-50.
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