International Journal of Open Educational Resources
Figure 1 . Zero Order Plot of Interaction Between OER and Course Difficulty
between OER use and course difficulty on student grades in that OER adoption appeared to lessen the negative relationship between course difficulty and final grades .
To address this study ’ s purpose , we calculated the unique measure of course difficulty based on the proportion of students who earned a D or F in each course . Because the study included multiple sections of many courses over multiple semesters , the calculation of current failure rate is arguably logical and stable . While course difficulty was ultimately dependent on individuals ’ course grades , the aggregation of failure rate across many sections and semesters did not result in undue multicollinearity , likely because of the large sample size involved .
The most important novel finding in this study , however , is the significant interaction between course difficulty and OER . The interaction term emerged in the presence of controlling for several potential confounds which typically “ consume ” available variance in multiple regression models predicting course grades . Finally , the interaction term emerged in the presence of a most powerful predictor , past student achievement . One potential explanation for this is that students ’ need for course materials to perform well in a course may increase with course difficulty . In other words , it is possible that students are able to manage in less difficult courses without access to course materials , but for the more difficult courses they need support beyond what is pro-
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