Food waste has also generally increased while glass and metals have decreased. Paper appears to be decreasing since 1977 as a proportion of the total. No consistent pattern is discernible from yard waste. Consistent trends are less clear from the reported total waste stream compositions. There is a general, but not consistent, pattern in growth in plastic as a proportion of the waste stream.
Food waste is indicated as roughly the same concentration as in a previous study.
Glass and metals have declined, but not consistently. For the sake of reference, the most recent EPA values for the composition of wastes disposed in the United States are included in Table ES-11 . In comparing the results of the historical waste characterization studies, it should be recognized that the studies were conducted using widely varying methodologies, numbers of samples, and material categories. Therefore, comparisons or generalizations from one study to another are influenced by both differences in definitions, sampling error, and perhaps some unknown sampling bias. Alameda County Waste Characterization Study was one of the largest such studies ever conducted in the United States.