EVIDENCE BOOK OVERVIEW
A. Evolution of the Evidence Book
The original Evidence Book is a collection of Evidence Reports created from the information presented verbally
and discussed within the NASA HRP in 2006. In April of 2008, the 2008 Evidence Book was reviewed by the members
of the Committee on NASA's Research on Human Health Risks, established by the Institute of Medicine (IOM). The
resulting thorough Review of NASA's Human Research Program Evidence Books: A Letter Report (2008) provided
guidance for both the revision of the current risk evidence reports and for the development of future versions.
It is publicly available via the
National Academies Press website.
Per the recommendations of the IOM Review, the Evidence Report information was made publicly available. The method
was either to publish the content of selected reports in multiple specialized journals or to publish a subset of
the reports in a collection, forming a NASA Special Publication entitled the HRP Evidence Book 2008. The
specialized journal publications containing the Evidence Report information were revised and reviewed per the
specifications of the particular journals in which they were published.
Since this original publication, the HRP Elements have continued to update each risk Evidence Report given results
from ongoing research and technology development (R&TD) tasks. The HRR contains the most up-to-date Evidence
Reports in the above table.
An archived publication entitled The Human Health and Performance Risks for Space Exploration Missions,
issued in 2009, is available for reference. Download a copy by clicking this
B. Spaceflight and Ground-Based Evidence
Each risk Evidence Report contains a narrative discussion of the risk and its supporting evidence. All cited
publicly-available references are listed at the end of the report. In addition, data that are significant or
pivotal are summarized in text, tables, and charts in sufficient detail to allow the reader to critique and draw
conclusions. The authors also indicate whether the data are from human, animal, or tissue, cellular, or molecular
studies. The reports discuss evidence from both spaceflight (including biomedical research, Medical Requirements
Integration Document [MRID] data, and operational performance or clinical observations) and ground (including
space analog research and non-space analog biomedical or clinical research) research. When providing evidence
from ground-based studies, authors discuss why these results are likely to be applicable in the space environment,
offering any available validation information for the use of these ground-based systems.
C. Categories of Evidence
To help characterize the type of evidence provided in the reports, authors are encouraged to label evidence
according to the "NASA Categories of Evidence". These categories indicate whether data are from two possible
types of controlled experiments, are observational, or are expert opinion. As shown below, the NASA categories
are compared with a more familiar version of a scale for levels of evidence. The use of a coordinated data
categorization system is new to many NASA life scientists, but authors are encouraged to use such a system to
help clarify the type of evidence presented and thus provide some additional information about the strength of
interpretations derived from those data. They are not required to use the categorization system hierarchically.
|Broad "Experimental" Design Type
||Silagy & Haines Levels of Evidence* (for comparison only)
||NASA Categories of Evidence
||Ia. Meta-analysis of randomized trials
||I. At least one randomized, controlled trial
|Ib. At least one randomized trial
|IIa. At least one controlled study without randomization
||II. At least one controlled study without randomization,
including cohort, case-control, or subject operating as own control
|IIb. At least one other type quasi-experimental study
||III. Non-experimental descriptive studies, e.g. comparative correlation, or case studies
||III. Non-experimental observations or comparative, correlation, and case or case-series studies
||IV. Expert committee reports or opinions or clinical experiences of respected authorities
||IV. Expert committee reports or opinions of respected authorities based on clinical experiences
bench research, or "first principles"
*Source: Silagy C,
Haines A. Evidence Based Practice in Primary Care, 2nd ed., London: BMJ Books, 2001.
D. Computer-Based Simulation Information
Mathematical modeling and computer simulation provide another type of information distinct from experimental
evidence, observation, and expert opinion that can support decision making, including the identification of risks.
In the Evidence Reports, authors present the results of simulations, the types of models used, and the reasoning
that supports the acceptance of the modeling and simulation results as valid and appropriate in the situation of
interest. Appropriate references to papers or reports describing the types of verification to which models were
subjected and the validation methods used are also provided.