3.3 - Exposure Measurement Techniques

Data can be collected by directly monitoring an individual or indirectly, each method with advantages and disadvantages.

1. Direct Method - Monitor individuals using some measurement device on their person.or by taking biological samples.

  • Personal monitoring: personal exposure monitors for particulate matter (PM), patches worn under clothing for pesticide applicators
  • Biological monitoring: lead concentrations in blood, biomarkers in urine, blood, breath, hair, nails

2. Indirect Method - Various possibilities--

  • Questionnaires/diaries
  • Job exposure matrix (JEM)
  • Environmental monitoring/modeling - monitor the environment and assume that people who live in that environment are exposed at the level observed at the monitoring site
  • Calculate the concentration of an agent in all locations/activities and multiply by the duration spent in each location/activity, (Examples: Indoor and outdoor exposure to ambient air particles, exposure to \(NO_2\) on the road)

Advantages and Disadvantages

1. The Direct Method

  • Provides exposure values with minimal assumptions
  • Assesses exposure and collects data at the individual level
  • May not be practical in a large epidemiological study because of the expense and effort required.
  • Heavily dependent upon ½ life of compound (how long it lasts in the body); may have affinity for certain tissues
  • Can be affected by inter-individual differences in metabolism, inter-laboratory variation and intra-individual variability due to diurnal variation, diet, season, etc.
  • If the chemical does not persist in the body, level will not reflect long-term exposure
  • An example: serum cotenine - this is a metabolite from tobacco smoking; measuring the cotenine level in serum reflects an individual's exposure to tobacco

2. The Indirect Method

  • Practical and less expensive, the indirect method has been used extensively in epidemiological studies
  • Often involves gathering data with a questionnaire.
  • Potential problems of a questionnaire: low response rate, non-responsiveness to an individual question, recall bias (not being able to remember), social desirability (false answers), low question validity and reliability.
Environmental Biomarker Research Example:
The US EPA is working to connect levels of environmental contamination to the risk of adverse effects in the public's health with the ultimate goal of reducing this risk. Check out the Chemical Safety for Sustainability Strategic Research Action Plan 2016-2019 to see how the EPA is working toward this goal. In particular, see Topic 2: Life Cycle Analytics, beginning on page 19.

Considering Four Types of Assessment: Questionnaires Section

  • Recall of exposure can be enhanced by question format
    • For example, ask questions that ask the participant to recall certain occupations and then go back and detail exposure for these occupations during their lifetime; can include a checklist of specific jobs, tasks, materials, other workplace exposures to minimize differential recall.
    • Job specific modules have been developed to elicit information systematically.
  • Open-ended questions: if needed, code by trained personnel
  • Clear wording at the appropriate reading level--no jargon
  • Avoid ambiguous quantities "regular" or "often" unless using Likert scale to assess preferences
  • Avoid overly detailed questions
  • Always consider the design, layout and overall order of the questions
  • May need to include a cognitive component for elderly populations
Example 3-3

Behavioral Risk Factor Surveillance System (BRFSS)

  • This is the world's largest, on-going telephone health survey system, tracking health conditions and risk behaviors in the United States yearly since 1984
  • Conducted by the 50 state health departments as well as those in the District of Columbia, Puerto Rico, Guam, and the U.S. Virgin Islands
  • Provides state-specific information about issues such as asthma, diabetes, health care access, alcohol use, hypertension, obesity, cancer screening, nutrition and physical activity, tobacco use, and more.
  • Federal, state, and local health officials and researchers use this information to track health risks, identify emerging problems, prevent disease, and improve treatment
Example 3-4: Questions from Colorectal Cancer Screening - BRFSS

CATI (Computer Assisted Telephone Interview) note: If respondent is < 49 years of age, go to next section. is

20.1 A blood stool test is a test that may use a special kit at home to determine whether the stool contains blood. Have you ever had this test using a home kit? (184)

  1. Yes
  2. No [Go to Q20.3]
  3. Don't know / Not sure [Go to Q20.3]
  4. Refused [Go to Q20.3]

20.2 How long has it been since you had your last blood stool test using a home kit? (185)

Read only if necessary:

  1. Within the past year (anytime less than 12 months ago)
  2. Within the past 2 years (1 year but less than 2 years ago)
  3. Within the past 5 years (2 years but less than 5 years ago)
  4. 5 or more years ago

Do not read:

  1. Don't know / Not sure
  2. Refused

20.3 Sigmoidoscopy and colonoscopy are exams in which a tube is inserted in the rectum to view the colon for signs of cancer or other health problems. Have you ever had either of these exams? (186)

  1. Yes
  2. No [Go to next section]
  3. Don't know / Not sure [Go to next section]
  4. Refused [Go to next section]

20.4 How long has it been since you had your last sigmoidoscopy or colonoscopy? (187)

Read only if necessary:

Do not read:

  1. Within the past year (anytime less than 12 months ago)
  2. Within the past 2 years (1 year but less than 2 years ago)
  3. Within the past 5 years (2 years but less than 5 years ago)
  4. Within the past 10 years (5 years but less than 10 years ago)
  5. 10 or more years ago
  6. Don't know / Not sure
  7. Refused

Are the above questions clear? What happens if questions are not clear?

Self-Reported Exposures

  • Many studies compare self-reported data to industrial hygiene measurements of exposure to one or a few agentst to validate the self-reported data
  • Self reports tend to give the 'usual' level, yet there is much day to day variability in exposure.
  • There is often large variation in reported agreement between self-reports and other measures

Self-reported Exposure Data Improves when

  • Subjects can sense exposure (smell, large particle sizes, vibrations…)
  • Queries use familiar language (e.g. 'degreaser' instead of using a specific chemical name)
  • The subject purchased or applied the chemicals (e.g. farmer)
  • Responses are prompted (e.g. give them a list of exposure agents)
  • Guides are provided to make relative comparisons, (e.g. noise equivalent to a vacuum cleaner)

Considering Four Types of Assessment: Occupational Histories Section

  • Are rarely validated against actual exposure data or even biomarkers
  • Can be compared to employer records (for validity-truthful?)
  • Can be compared to previous self-report (reliability - same answer at different times?)
  • Factors that reduce validity and reliability of questionnaires
    • Complex occupational history
    • Longer period of recall
    • Short duration of job
  • Internal validity and reliability can be checked within a study; e.g. take a random 10% sample and re-administer a critical part of the occupational history tool.

Sensitivity, specificity, the Kappa, \(R^2\) can be calculated for these measures.

Using a Job Exposure Matrix is another way to measure relative exposure. Samples are taken to characterize exposure to a compound by workers in particular jobs. An example of a JEM is posted in ANGEL: Hopf, et al. (2009). Cumulative exposure estimates for polychlorinated biphenyls using a job-exposure matrix. Chemosphere 76 (2) 185-93. Job Exposure Matrices have their advantages and disadvantages as well.

Advantages of JEM:

  • JEMs are available for a wide range of occupational exposures
  • Provides exposure ranking that is not subject to recall bias
  • Can be applied to large population databases (e.g. Sweden)
  • Estimates of probability can be used to stratify the relative risk or odds ratio calculation

Disadvantages of JEM:

  • JEM categories may not be comparable across studies
  • Misclassification more likely in high occupational exposures
  • Time consuming to develop
  • May be highly dependent on the expert providing a rank
  • Only some JEMs have been correlated well with biomarkers
  • "Generic" JEMS may perform less well than study-specific

Considering Four Types of Assessment: Expert Assessment Section

Do experts have a better vantage point? Do experts always say the same thing?

  • We assume experts have better vantage point to assess exposure; however, they may not know the exact conditions present in the work situation of each subject
  • Experts may use different sources---E.g. One expert could use self-reported data to make the judgment of exposure level while another devises a study-specific JEM based on literature or a database.

Various factors affect the validity and reliability of expert assessment of exposure:

  • The agent
  • Expertise of assessors
  • Whether or not agent can be sensed
  • Whether assessing a broad class or a specific agent
  • Expert estimates are generally better than self-reports
  • Improve Reliability and Validity
    • By giving the expert assessor access to data that may improve their estimate—subject reported exposure data, work conditions and measurement data

Considering Four Types of Assessment: Direct Exposure Measurements Section

In an ideal situstion, you can measure exposures directly. A cohort or cross-sectional study may offer the opportunity to measure exposure directly. Questions to ask in this process include the following: how many samples are required? should subjects be grouped and if so, how?

Quantitative data from an existing database could also be available to an investigator. For example, ionizing radiation exposures have been recorded since 1950; certain records are required from mines. Given recent international trends toward data-sharing, more records should become available.

Using records from an existing database requires calculating an estimate of average exposure for a worker when no individual identifiers are associated with the data. If the database is not from the actual worksite of interest, validity and reliability studies are recommended.

Techske et al (2002) state that the highest priority in an environmental or occupational case-control study is measuring exposure. Most of the time we consider defining controls to be the most important part of a case control study. Do you agree with Techske? Why or why not?