From the datasets downloaded from the Directory of Open Access Journal, we did some analysis. We found that among the journals that do offer article processing charges (APC), 87 % of them offer variations. So that the APC that the author expects to pay could be higher or lower. Those fluctuations depend on many factors. For example an article that requires language editing would have higher APC and if the author comes from a low/medium income countries then the APC will decrease. The table one shows the percentage of journals offering variations in pricing. The table 2 shows the list of the most frequent factors that contribute to APC variations.
Table 1. Percentage of journals offering variations in pricing (2015).
Table 2. Frequency of sub-types of variations.
Please note that we did not count every variation found. For example, variations likely based on simultaneous print versions of journals such as colour charges were not capture.