Further analysis of Aiken et. al.'s study illustrates a breakdown of the study's components, enumerated and discussed below: Hypothesis

There is a significant relationship between nurses' education and patient outcomes.

Study design

The research is a cross-sectional study that sought to confirm the researchers' hypothesis (stated above) among 232,342 general, orthopedic, and vascular surgery patients from 168 general hospitals in Pennsylvania.

Variables

Variables under study were nurses' educational levels and patient outcomes; additional variables included were nurses' workload and work experience. Patient outcomes were measured through patient mortality and failure-to-rescue rates.

Classification of variables

Nursing education level was...

The former was identified as an ordinal type of variable, while the latter is an interval/ratio variable type.
Instrument validation

Since most information were generated from extant data from hospitals, checks were conducted by researchers to ensure that hospital data used for determining patient mortality and failure-to-rescue rates have integrity, are clean and official, and were obtained from a very credible source -- Pennsylvania Health Care Cost Containment Council (1619).

Reference used:

Aiken, L., S. Clarke, R. Cheung, D. Sloane, and J. Silber. (2003). "Educational levels of hospital nurses and surgical patient mortality." The Journal of the American Medical Association. Vol. 290, No. 12.