Mineral Resources On-Line Spatial Data
National Geochemical Survey
Analysis of Variance (AOV) Methods in the NGS
The methods used to collect samples for analysis of variance are described with the sampling protocol for each dataset. Basically, two procedures were used, and there are two data fields that store relevant information.
- AOV_CODE. In areas where sample collection was based on a grid, with cell sizes
usually either 10x10 km or 17x17 km, certain cells were designated for analysis of variance. AOV_CODE is used to indicate samples that were collected in these AOV cells. Values in this field are:
- D1 = The sample is the primary one collected in the cell.
- D2 = This is a second sample, collected in a different quarter of the cell than the D1 sample.
- D3 = This is a third sample, collected 50-100 m upstream from the D2 sample.
- D4 = This is a fourth sample, made by taking a split of the D3 sample in the laboratory.
- D5-D9 = Used for additional AOV samples taken in the cell (rarely used)
When archives of pre-existing samples were used as a source of material for re-analysis, as was the case for all NURE samples in the NGS, a small percentage of samples were selected for replicate (usually duplicate) analysis. Pre-existing datasets that were incorporated into the NGS may also have contained replicate analyses of some samples. Codes for these samples are:
- R1 = The sample is the first of 2 or 3 replicates.
- R2 = The sample is the second of 2 or 3 replicates.
- R3 = The sample is the third of 3 replicates.
There is no significance to the order of samples labeled R1, R2, and R3.
The field is used to identify AOV or simple replicate samples that belong together. The field
may contain two types of information:
- The word "first". This indicates that the sample was either
replicated or is the primary AOV sample in the cell. There are other records associated with this record in the database.
- A laboratory number. This indicates that the record with LABNO equal to this value is the primary record with which this one is associated. This sample is either an AOV sample or a replicate sample, depending on the value in AOV_CODE.
Thus if a sample was analyzed in duplicate, the two records in the database might appear with the LABNO, AOV_CODE and REPLICATE fields as follows:
A series of samples from an AOV cell might appear with the LABNO, AOV_CODE and REPLICATE fields as follows:
Note: there are cases where the primary sample in an AOV cell was lost or not analyzed. In these cases, the D2 sample will contain the word "first" in the REPLICATE field.
U.S. Department of the Interior, U.S. Geological Survey
This page is part of U.S. Geological Survey Open-File Report 2004-1001
Maintained by Jeff Grossman
Last modified: 09:05:14 Wed 14 Mar 2012
Privacy statement | General disclaimer | Accessibility