Borkovec, T. D., Robinson, E., Pruzinsky, T., & De Pree, J. A. (1983). Preliminary exploration of worry: Some characteristics and processes. <i>Behaviour Research and Therapy</i>, 21, 9-16.
Flavell, J. H. (1987). Speculations about the nature and development of metacognition. In F. E. Weinert, & R. H. Kluwe (Eds.), <i>Metacognition</i>,<i> Motivation</i>,<i> and Understanding.</i> Hillsdale, NJ: Lawrence Erlbaum Associates. pp. 21-29.