@misc{indiciaea6c81e3cce04,
  title = {The qualification period.},
  author = {P Knipschild and P Leffers and A R Feinstein},
  year = {1991},
  doi = {10.1016/0895-4356(91)90208-q},
  url = {https://pubmed.ncbi.nlm.nih.gov/2037850/},
  note = {Source identifier: 2037850}
}