## Conditional Probability Analysis: Chlorophyll a > 30 vs. Total Phosphorus for Northeast Lakes

### Plot

- Analysis: Conditional probability analysis
- Independent variable: Total phosphorus concentration in upper water column (ug/L)
- Dependent variable: Probability of unacceptable condition for chlorophyll a at > 30 (ug/L)
- Key: symbols = observations, dashed line = 95% Confidence Intervals
- Sample size: N = 483

### Model

- Conditional probability analysis does not produce a model equation. Rather, it plots the probabilities of observing the stated impairment (i.e. item 3 in the list above) over a stressor intensity gradient.
- Date: 8 November 2006

### Data Analysis

- Program: S-Plus Version 7.0, user written scripts, variable weighting for site data

### Data Origin

- Agency: U.S. Environmental Protection Agency
- Program: Environmental Monitoring and Assessment Program (EMAP).
- Project: Surface Waters, Northeast Lakes Data
- Location: Northeast United States

### Sampling Design

- Data collected using the EMAP probability design over July through September in 1991 through 1994.
- Single grab sample at 1.5 m below surface with van Dorn sampler according to Baker, JR, GD Merritt and DW Sutton (eds.). 1997. Environmental Monitoring and Assessment Program - Surface Waters: Field Operations Manual for Lakes.
- Catalog Documentation for EMAP Surface Waters Northeast Lakes Data, EMAP.

### Contact

John F. Paul, paul.john@epa.gov, (919) 541-3160