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We are having problems performing correlation analysis on data obtained from GC chromatograms. As the extraction efficiency of the samples is highly variable we are expressing individual peaks as a percentage of the total peaks area. The problem then is that the Limit of Detection (LOD), which we are defining as the smallest peak that the integrator can handle divided by the total peaks area, changes with the extraction efficiency for each sample. We are now trying to correlate the percentage of each compound (as a fraction of the total) as detected by GC with other continuous biochemical and anthropometric variables. Deleting the data which is below the LOD is going to skew the analysis and reduce power. Ranking all the 'below the LOD' data as equally low results is also incorrect as the samples that extracted very poorly could have results higher than some of the defined data. Is there a formal treatment for these sort of data? If not any ideas? Thanks in advance. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%