Table 1.

Table 1 Hierarchy of Study Designs

Level	Study design	Description
I	Randomized Controlled Trial (RCT)	A study in which people are allocated at random (by chance alone) to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The investigator controls the exposure to the intervention.
II	Non-Randomized Controlled Trial	A study in which people are allocated to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The investigator controls the exposure to the intervention but allocation of people is not based on chance. It includes interrupted time series and before-after studies.
III	Observational study with controls	A study in which individuals are observed or certain outcomes are measured without a specific attempt to affect the outcome (the investigator does not control the exposure to the intervention, e.g., the use of a CPOE). The intent is to observe how exposure to risk factors (implemented CPOE) influences the outcome of interest. Includes cross-sectional studies to estimate the prevalence of the outcome of interest or the prevalence of exposure to intervention or both; cohort (longitudinal) studies with control in which individuals who are exposed to the intervention are followed for a defined length of time and the effects of the intervention on the exposed group is compared to a group that was not exposed; and case control studies in which a comparison of exposure to the CPOE in a group of individuals with the outcome of interest (cases) is compared to those without the outcome of interest (controls).
IV	Observational study without controls	Includes cohort studies without controls or case series.