Fig 1.
From all journals listed with an Impact Factor (IF) in the Science Citation Index (SCI) or Social Sciences Citation Index (SSCI), those were selected for further analysis which showed a change of the IF (ΔIF) equal or greater than a threshold of 3.0.
Fig 2.
Range of Impact Factor changes (ΔIF) for 2014 versus 2013.
(A) ΔIFs for all 10,754 journals with a listed IF for 2013 and 2014. (B) ΔIFs for the journals (n = 49) in the selected study cohort (threshold ΔIF ≥ 3.0). In- and decreasing IFs are highlighted green or red, respectively. The 49 journals in the sample cohort are subsequently identified by a unique identifier (#1 - #49).
Fig 3.
Possible scenarios explaining a changing Impact Factor (IF).
(A) Based on theoretical considerations regarding the potential influence of the variables (citations and article numbers) on the final calculation (i.e. the IF quotient), 13 scenarios are possible which either cause an increased (a1-a5), constant (b1-b3) or decreased IF (c1-c3). In those scenarios where necessary, the size of the arrows indicate the relative importance of the changes (articles (Δ(art)) versus citations (Δ(cit))). (B) The validity of these IF changes as a parameter of (changing) journal quality is categorized and referred to as either ‘valid’ (highlighted green) or ‘invalid’ (highlighted red). See text for further explanation.
Table 1.
Observed maximum changes of citations, articles and Impact Factors.
Fig 4.
Annual changes of the Impact Factor (IF) and its variables (citation versus article numbers).
For the annual changes (A-D) of the IF, the relation of relative changes of the number of citations versus articles is shown in each diagram by blue and grey columns, respectively. Each column shows the relative change (%) in relation the numbers of citations or articles in the preceding year. Below each diagram, the ΔIF for each annual step is classified ‘invalid’ as defined in Fig 3 and indicated by a red box behind the journal ID. The 49 journals in the sample cohort are identified by a unique identifier (#1 - #49).
Fig 5.
Summary of observed scenarios / variants of changing Impact Factor (IF).
(A) IF increases (left bars) and decreases (right bars) for each annual step 2010–11 to 2013–14. IF increases are further classified as valid or invalid according to the classification in Fig 3. (B) The observed IF changes (n = 179) over the four annual steps are classified according to the scenarios explained in Fig 3 and illustrated for their relative frequency. Invalid IF changes (a3 and a4) are highlighted by red boxes. (C) Overall distribution of journals regarding to the validity of their IF changes. (D) Longitudinal development of each journal in the sample cohort. IF increases, IF decreases and invalid IF increases are indicated by green / red color or red boxes, respectively.