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Analysis and Reporting Methods
This section provides detailed information or links for:
Analysis
Testing, estimation and comparisons
- Trend Detection
- Population Estimation for Site Evaluation Categories, Continuous Indicators and Indicator Status
Summarizing the Information
Once the units have been selected and data obtained, a statistical summary is needed. For a public opinion poll, the summary may be as simple as the percentage of people who state that they plan to vote for a particular candidate. How the percentage is calculated depends on the survey design used to collect the data. When the survey design is a simple random sample, the percentage is calculated simply as the number of respondents who plan to vote for the candidate divided by the total number of respondents and multiplied by 100 to convert to a percentage. If the survey design is more complex (and most are), then the calculation is more complex but conceptually the same. The same is true for aquatic probability survey designs. The analysis can not be done independent of the design.
Examples:
- Miles of Oregon Streams
- Chemical vs Biological Impairment, Oregon Streams, Ohio Stations
- Impaired Macroinvertebrate Conditions
- Aquatic Vertebrate Species Status
- South Carolina - Estuaries - IBI
Reporting
EPA Region 4: Poster Presentation of Preliminary results on mercury in fish from Southeastern wadeable streams.
Communicating Results
No sample survey is useful until the results are promptly and unbiasedly communicated to the intended audience. A carefully conducted probability survey can be negated by how a report is written. Reports of a public opinion poll may re-phrase the question asked on the questionnaire, giving readers a different impression of the question's meaning. Results may be reported as percentages and not actual values, giving the impression that a problem is a minor issue rather than impacting millions of people. Graphs may be constructed to emphasize a particular point of view. Similar issues arise with aquatic monitoring.