Incorporating uncertainty associated with censored water quality data in parametric trend analysis

Technical Report · Tue Jun 01 00:00:00 EDT 1993

OSTI ID:5981504

Water quality data are often collected in monitoring programs to serve as a basis for the estimation of trends. A problem arises in trend estimation when data series contain observations reported as below detection limit (BDL). The several published methods that deal with BDL observations are generally oriented towards obtaining the best value to substitute for the censored values. When the definition of a detection limit associated with a datum is unknown, a conservative lower bound (with a theoretical justification) for the precision of the observation is given. The results show that weighted regression estimates of linear trends are much less sensitive to the method of substitution for BDL values than unweighted regression trend estimates. The results also indicate that use of weighted regression in multiply censored data series eliminates the need to apply the highest detection limit to all data in the series (when data below this highest limit exist in the data series) in order to avoid trends due to changing detection limits.

• Research Organization: Environmental Protection Agency, Annapolis, MD (United States). Chesapeake Bay Program
• OSTI ID: 5981504
• Report Number(s): PB-93-208262/XAB; CBP/TRS-75/93
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
WATER QUALITY
MONITORING
CHESAPEAKE BAY
DATA COVARIANCES
FORECASTING
MANAGEMENT
NUTRIENTS
PARAMETRIC ANALYSIS
THEORETICAL DATA
WATER CHEMISTRY
WATER POLLUTION
ATLANTIC OCEAN
BAYS
CHEMISTRY
COASTAL WATERS
DATA
ENVIRONMENTAL QUALITY
INFORMATION
NUMERICAL DATA
POLLUTION
SEAS
SURFACE WATERS
540320* - Environment
Aquatic- Chemicals Monitoring & Transport- (1990-)