Are open-book tests still as effective as closed-book tests even after a delay of 2 weeks?

The present work was conducted to re-examine the findings of Agarwal et al. (Applied Cognitive Psychology, 22(7), 861–876, 2008), which showed that both closed-book tests (with feedback) and open-book tests increased learning outcomes after 1 week compared to simple re-study of the same materials. However, contrary to often found benefits of retrieval practice—which should be more pronounced in closed-book tests—both test conditions proved to be similarly effective. As retrieval practice benefits increase with retention interval, this pattern may change with a longer delay. Hence, we conducted a laboratory study and applied three within-participant learning conditions (re-study, open-book test, closed-book test with feedback) with a 2 weeks instead of 1 week delay between studying and the final test. Notably, our results mirrored the findings of Agarwal et al. (Applied Cognitive Psychology, 22(7), 861–876, 2008) showing that open-book and closed-book tests outperform re-study but are similarly effective—even using a slightly changed procedure, new materials, a different sample, and a longer delay.