Evaluating Limitations
This section explains how to evaluate potential limitations at your site. It shows you how to describe the limitations, determine if the limitations could affect your conclusions, and identify recommendations to address the limitations.
Throughout the PHA process, you must evaluate potential limitations in the available information and determine whether critical data are available and sufficient to support a public health conclusion. If critical data are missing, consider recommending actions to help fill those data gaps. You can use the Potential Limitations table [PDF – 174 KB] to help identify and navigate the potential limitations.
In some cases, you might need additional data to confirm or further support your decision. Carefully examine the importance of the missing data, whether you can obtain the needed data, and if you can obtain it in a timely manner. In some cases, the data might never be available (e.g., past exposure data), so you will need to use the best available data (e.g., more recent sampling data or in limited circumstances modeled data) to evaluate potential hazards and draw conclusions.
If you determine that available data are insufficient to draw a conclusion, clearly indicate this in your written document. Also, recommend additional actions when possible and state that a definitive conclusion cannot be drawn because of the absence of critical data.
Not all data gaps are data needs. Before recommending sampling or further investigation, carefully assess and distinguish what would be good to know versus what is needed to draw a public health conclusion. Also consider issues that the community needs to know or that it might reasonably expect ATSDR to address. Provide as much perspective as possible using available data.
You will need to clearly explain in your documents what is known and not known, and where and why there are limitations. Also, in your conclusions, state how you accounted for uncertainties related to these limitations. Whenever possible, ATSDR accounts for limitations by using protective, reasonable exposure estimates as the basis for determining whether harmful health effects are possible (see the Potential Types of Limitation Sources and Examples Table).
Types of Potential Limitation Sources |
Examples of Potential Limitations by Source |
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Measurements/ sampling data |
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Modeling* |
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Exposure units |
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Exposure point concentrations |
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Exposure doses |
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Site-specific population |
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Health guidelines and cancer risk values |
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Studies used to support analysis |
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*Note: Modeling data can be used to supplement the available sampling data in limited circumstances. Health assessors need to discuss the appropriateness and feasibility of using modeled data beforehand with subject matter experts (SMEs).