Glossary

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9

95% Confidence interval for the geometric mean

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.

95% Confidence interval for the geometric mean - lower

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.

95% Confidence interval for the geometric mean - upper

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.

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B

Below the limit of detection (<LOD)

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.

birth cohort

A group of people who were all born during a specified time period.

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C

case-control study

A study that compares people who have a disease or outcome of interest (cases) with people who do not have the disease or outcome (controls).

CASRN - Chemical Abstract Services Registry Number

The CASRN is a unique identification number assigned to individual chemicals by the Chemical Abstract Services division of the American Chemical Society.

CDC

U.S. Centers for Disease Control and Prevention

CDPH

California Department of Public Health

Chemical measured

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.

cohort

Refers to a group of individuals who have something in common, such as sharing a particular experience (e.g., Class of 2016) or characteristic (e.g., people who do not have cancer). For example, see birth cohort.

cohort study

A study that follows a group of people who do not have a disease or outcome of interest for a period of time to see who develops the disease or outcome.

convenience sampling

In convenience sampling, sample data are collected from groups of people chosen based on ease of access for the researcher. Some examples of a convenience sample include a group of friends or coworkers. Convenience samples may not be representative of the larger population.

Creatinine-adjusted concentrations

Creatinine is a normal byproduct of metabolism that is found in urine. A creatinine-adjusted concentration takes into account how dilute or concentrated a urine sample is.

cross-sectional study

A study that measures the occurrence of disease or exposure in people at one particular time point.  Also known as a prevalence study.

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D

Detection frequency (percent detected)

The percentage of study participants with a measurable level of a chemical in their blood or urine sample.

DTSC

Department of Toxic Substances Control

DTSC's

Department of Toxic Substances Control's

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E

Environmental breakdown product

A new chemical that forms when another chemical is changed through the action of bacteria or sunlight, or other processes that occur in the environment. Environmental breakdown products are sometimes measured in biomonitoring studies (e.g., DDE, an environmental breakdown product of DDT).

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F

Full Project collaboration

Biomonitoring California designed and carried out the entire study in partnership with other organizations. This involved choosing the population; recruiting participants; designing and administering exposure questionnaires; collecting blood and urine samples; conducting laboratory analyses; and reporting results to participants.

full project collaborations

Biomonitoring California designed and carried out these entire studies in partnership with other organizations. This involved choosing the population; recruiting participants; designing and administering exposure questionnaires; collecting blood and urine samples; conducting laboratory analyses; and reporting results to participants.

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G

Geometric mean

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.

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I

Indicates exposure to

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.     

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L

Laboratory collaboration

Biomonitoring California laboratories conducted analyses of blood and/or urine samples collected by outside partners as part of other research projects.

laboratory collaborations

Biomonitoring California laboratories conducted analyses of blood and/or urine samples collected by outside partners as part of other research projects.

Limit of detection (LOD), wet-weight

The limit of detection (LOD) is the lowest level of a chemical that the laboratory can measure in whole blood, urine or serum. The wet-weight LOD 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 will differ from the units used to report the biomonitoring results.

Lipid-adjusted concentrations

Some chemicals measured in an individual’s blood are affected by his or her levels of cholesterol and other fats in blood (known collectively as lipids). A lipid-adjusted concentration takes this effect into account and is reported as, for example, nanograms per gram of blood lipid (ng/g).

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M

MAMAS

Measuring Analytes in Maternal Archived Samples

Metabolite

After a person is exposed to a chemical, the body may modify the chemical’s structure, forming a new chemical. This new chemical is called a metabolite. A metabolite is sometimes the best indicator of exposure to the parent chemical.

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N

nested case-control study

A case-control study in which both cases and controls are selected from people enrolled in the same cohort study.

Number of people tested

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

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O

OEHHA

Office of Environmental Health Hazard Assessment

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P

PAH

polycyclic aromatic hydrocarbons

Parent chemical

We use this term to describe the chemical to which a person is originally exposed. Parent chemicals could include, for example, chemicals in consumer products, pesticides, or contaminants in air, drinking water and food. A parent chemical may be converted to a metabolite through various processes in the body.

part per million

One part per million (also called “ppm”) can be envisioned as one drop of a substance in about 13 gallons of water.

Participants

People who have been selected and have agreed to be a part of a project.

parts per million

One part per million (also called “ppm”) can be envisioned as one drop of a substance in about 13 gallons of water.

Population

A population is the entire group of people about whom inferences will be made, based on sample data.

ppm

One part per million (also called “ppm”) can be envisioned as one drop of a substance in about 13 gallons of water.

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R

random sampling

In random sampling, sample data are collected from groups of people chosen by chance. Each member of the larger population has a known, possibly unequal, chance of being included in the sample.

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S

Sample collection date

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

Sample data

Sample data are collected from a subset of a larger population using various approaches, including random sampling and convenience sampling. Sample data from a small group of people are used to make inferences about the larger population.

Selected percentiles

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

Selected percentiles - 25th

If the 25th percentile is 0.3 µg/L, for example, this means that 25% of participants had levels less than or equal to 0.3 µg/L.

Selected percentiles - 50th

If the 50th percentile is 0.6 µg/L, for example, this means that 50% of participants had levels less than or equal to 0.6 µg/L.

Selected percentiles - 75th

If the 75th percentile is 1.2 µg/L, for example, this means that 75% of participants had levels less than or equal to 1.2 µg/L.

Selected percentiles - 90th

If the 90th percentile is 1.5 µg/L, for example, this means that 90% of participants had levels less than or equal to 1.5 µg/L.

Selected percentiles - 95th

If the 95th percentile is 1.9 µg/L, for example, this means that 95% of participants had levels less than or equal to 1.9 µg/L.

Serum

The liquid portion of a blood sample that remains after blood clotting proteins and red and white blood cells have been removed.

Study group

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

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U

Units

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.

Units used by Biomonitoring California

Examples of units used for urine measurements:

  • µg/L urine: Amount of chemical in micrograms per liter of urine.
  • µg/g creatinine: Amount of chemical in micrograms per gram creatinine. For more information follow this link: creatinine-adjusted concentrations.

Examples of units used for whole blood measurements:

  • µg/L whole blood: Amount of chemical in micrograms per liter of whole blood.
  • µg/dL whole blood: Amount of chemical in micrograms per deciliter of whole blood. A deciliter is one tenth of a liter.

Examples of units used for serum measurements:

  • µg/g lipid: Amount of chemical in microgram per gram lipid. For more information follow this link: lipid-adjusted concentrations.
  • µg/L serum: Amount of chemical in micrograms per liter of serum.
 

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