MLA
Oberg, Kathryn J. An Investigation of Reference Question Difficulty Over Time. 2011. https://doi.org/10.17615/j4pv-hw82
APA
Oberg, K. (2011). An Investigation of Reference Question Difficulty over Time. https://doi.org/10.17615/j4pv-hw82
Chicago
Oberg, Kathryn J. 2011. An Investigation of Reference Question Difficulty Over Time. https://doi.org/10.17615/j4pv-hw82