mussels: Concentrations of PAH contaminants in Casco Bay blue mussels.
In ccb60/LCensMeans: Calculate Condtional Means of Left Censored Data

A dataset containing concentrations of PAH contaminants from blue mussels (Mytilus edulis) from Casco Bay, Maine, USA. All concentrations are in ng/g, or (approximately) ppb.

mussels

A data frame with 780 rows and 5 variables:

Site: A four-letter site code. Casco Bay sites include "MEPH" for Portland Harbor, "MEPR" for the Presumpscot River estuary, "MYRY" for the Royal River Estuary, and "MEBC" for Broad Cove.
Year: Year the sample was collected, as an integer
PAH: Chemical name, as a string. Note that many of the chemical names can not be used as syntactic names in R.
Flag: Logical (TRUE/FALSE) value indicating whether the specific contaminant was detected or not. A TRUE value means the associated compound was not detected. The Concentration value then represents the associated detection limit.
Concentration: Concentration expressed in ng/g. Value either represents the observed value (if Flag == FALSE) or a related detection or reporting limit (if Flag == TRUE).

Data are derived from NOAA Gulfwatch data collected from 1993 through 2000.

Data exhibits many of the challenges of working with non-detects, in a small, compact form.

Some compounds were observed all or almost all the time.
Some compounds were not sampled every year, generating missing values
Some compounds were detected rarely, or even never detected.

Note that format of data follows a specific convention for handlign non-detects. One data column contains a column of concentrations (including detection/reporting limits for "Non-detects" and a column if flags (logical TRUE/FALSE values) indicating which values represent non-detects.

https://gulfofmaine.org/public/gulfwatch-contaminants-monitoring/findings/

ccb60/LCensMeans documentation built on Oct. 30, 2020, 3:26 a.m.