Project Results for California Childhood Leukemia Study (CCLS)

A 95% confidence interval for the geometric mean (CI-GM) is a range of values between two numbers called the lower bound and upper bound. These bounds are calculated based on sample data collected from a subset of a larger population. In repeated random sampling, the CI-GMs calculated for the various samples will contain the population value of the geometric mean 95 percent of the time. If convenience sampling is used to collect sample data, the CI-GM should be interpreted with caution. This is because a convenience sample may not be representative of the larger population.

A 95% confidence interval for the geometric mean (CI-GM) is a range of values between two numbers called the lower bound and upper bound. These bounds are calculated based on sample data collected from a subset of a larger population. In repeated random sampling, the CI-GMs calculated for the various samples will contain the population value of the geometric mean 95 percent of the time. If convenience sampling is used to collect sample data, the CI-GM should be interpreted with caution. This is because a convenience sample may not be representative of the larger population.

Chemical concentrations in urine can be adjusted for urine dilution using creatinine or specific-gravity. Chemical concentrations in serum can be adjusted for lipids. In the results tables, unadjusted chemical concentrations are denoted by NA.

Below the limit of detection (< LOD) means that the laboratory could not detect the chemical. This may have been because the chemical was not present at all or because it was present at such a low level that the laboratory could not measure it.

Below the limit of quantification (<LOQ) means that the chemical was not present or that it was present at such a low level that the laboratory could not measure it quantitatively with acceptable accuracy.

The chemical that was analyzed in blood or urine samples. The chemical measured is sometimes the parent chemical and sometimes a metabolite of the parent chemical.

The percentage of blood or urine samples with a measurable level of a chemical.

The geometric mean is an estimated middle value of a set of numbers.This is different than the average, also called the "arithmetic mean". A geometric mean is sometimes calculated when the set of numbers contains some extreme values. For example, the geometric mean of the set of numbers "1, 2, 2, 3, 4, 5, 5, 6, 10, 100" is calculated by multiplying all ten numbers together and then raising to the 1/10th power, giving 4.8. To compare, the arithmetic mean is calculated by adding all ten numbers and dividing by 10, giving 14. 

In the data tables, an asterisk (*) means the geometric mean was not calculated because the chemical was found in less than 65% of the study group.

The chemical(s) listed in this column is the chemical(s) to which a person may have been exposed through various sources (e.g., via drinking water or use of a consumer product).  This chemical is commonly called the parent chemical.    

The number of individuals whose blood or urine samples were analyzed for a particular chemical.

The limit of detection (LOD) and limit of quantification (LOQ) are indicators of the lowest level of a chemical the lab can measure with acceptable accuracy and precision. For some projects, this is reported as an LOD. For others, it is reported as an LOQ. The wet-weight LOD/LOQ is presented as an amount of a chemical per liter of a sample (for example, microgram of a chemical per liter of urine, or µg/L). This is often the way that biomonitoring results are reported as well (for example, µg/L urine or µg/L serum). In some cases, however, biomonitoring results are presented as lipid-adjusted concentrations (µg/g lipid) or creatinine-adjusted concentrations (µg/g creatinine). For these cases, the units for the wet-weight LOD/LOQ will differ from the units used to report the biomonitoring results. For more information on lab results and protocols, please contact us.

The time period during which blood or urine samples were collected from participants in Biomonitoring California projects or laboratory collaborations.

A range of values calculated to show the distribution of measured chemical levels. See specific percentiles below for examples.

A brief description of the people who provided blood and/or urine samples for analysis in a particular study. 

Human biomonitoring data are commonly reported as an amount of a chemical present in a specified volume of a bodily fluid (such as blood or urine). For example, a chemical measurement expressed in units of µg/L urine tells us the number of micrograms (µg) of the chemical present per one liter (L) of urine. Using standard units allows for comparison across different studies. For more examples, see definition for: Units used by Biomonitoring California.

Unweighted results summarize the measurements collected from study participants but may not apply to a wider group of Californians.

Weighted results are results that have been calculated using a statistical method that adjusts over-represented and under-represented samples. Weighted results adequately reflect a wider population in California.