Human Exposure Assessment for Airborne Pollutants Advances and Opportunities (1991) / Chapter Skim
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5 Survey Research Methods and Exposure Assessment
5 Survey Research Methods and Exposure Assessment
Pages 143-168
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From page 143... ...
found notable departures from sound survey practice; even the most sophisticated and laudable efforts toward improving survey quality, such as the standardized Environmental Inventory Questionnaire, contain some problematic survey practices. Properly designed and conducted survey research can provide the precise population estimates needed for exposure assessment relatively inexpensively.
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From page 144... ...
· Deciding on the most appropriate measurement approach in exposure assessment, these include personal exposure monitors combined with timeactivity diaries (direct) , time-activity diaries alone (indirect)
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From page 145... ...
Direct approach (personal monitor and tim~activity diaIy3 Indirect approach (time-activity diary alone) Questionnaire approach Open versus closed questions Single versus multiple items Long versus short questions Explicit versus implicit questions Aspects of time man (1988~.
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From page 146... ...
Survey researchers can ask how often an individual respondent might have been in a situation that was likely to involve significant exposure, but the respondent's memory of such occasions is extremely problematic. Research on respondent memory has revealed a host of biasing factors and ambiguities (Tulving, 1983; Bradburn, 1987; Pierson et al., in press)
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From page 147... ...
· Assuming that a probability sample has been drawn, that nonresponse bias is negligible, and that measurement error also is negligible, statistical formulas should be used to calculate the sampling error of an estimate based on the sample. Calculated estimates of precision are not appropriate if the response rate is low or if there are substantial measurement errors or problems.
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From page 148... ...
Samples not based on probability sampling methods are often used in preliminary stages of exposure assessment. For example, investigators might conduct a pilot study of a new instrument on their colleagues or on volunteers.
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From page 149... ...
Low response rates warrant careful scrutiny, because they raise the possibility of substantial nonresponse bias. If respondents and nonrespondents are different, the data collected on the respondents are of questionable generalizability to the entire target population.
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From page 150... ...
For a simple random sample taken to estimate a specified population proportion (e.g., smokers or persons exposed to a specified contaminant on a particular day) , sampling error is calculated according to the following equation: sampling error = [(p)
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From page 151... ...
Following the same individuals across time provides an essential perspective for future exposure-assessment studies. MEASUREMENT APPROACHES The process of exposure takes place across time, and exposure assessment needs to be sensitive to the time element in all data collections.
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From page 152... ...
In the indirect approach, exposure is imputed from the activities that respondents report in time-activity diaries. In the more traditional questionnaire approach, exposure is imputed from responses to self-reported factual questions (e.g., occupation, age of dwelling unit, and fuels used for heating and cooking)
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From page 153... ...
The main advantage of the indirect approach is that it places less burden on respondents than personal monitoring and is thus able to achieve higher response rates. Time-activity data can be obtained with several procedures, such as estimation by respondents in the study sample, by direct observation, or from timeactivity diaries.
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From page 154... ...
An important exception is the current statewide study being conducted by CARB. The CARB study was designed specifically for exposure assessment, and it measures periods of exposure to environmental tobacco smoke, time spent in specific rooms in the home, and occurrences of exposure to solvents and other pollutants (Robinson et al., 1989~.
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From page 155... ...
One can estimate with some precision how much time a target population spends working on automobiles, going to the dry cleaners, cooking meals, and, at least theoretically, any other activity that takes place. Of more concern is the possibility of estimating time spent in microenvironments, such as outdoors in transit or at home' etc.
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From page 156... ...
As detailed and focused as the CARB survey was for exposure research, it did not include information on the general health status of the respondents, their exact distances from possible pollutants, their breathing rates during activities, or open spaces in their workplaces or home. Moreover, the activity analyses were confined to a single day for each respondent.
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From page 157... ...
? · Who is in the target population and the sampling frame?
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From page 158... ...
. Diary data can be used to identify population groups whose activity patterns can lead to large exposures and to identify their special demographic features (e.g., younger people or urban residents)
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From page 159... ...
Similarly, questions about use of pesticides and herbicides outdoors refer only to episodes longer than 1 hour over the previous 6 months, whereas shorter duration or frequency of use need to be considered as well. Finally, the EIQ asks a number of factual questions about number of rooms and construction materials.
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From page 160... ...
QUESTIONNAIRE FRAMING AND WORDING Questionnaire results are subject to measurement error in the same way as physical and chemical measurements based on personal monitors. Both questionnaires and monitors can produce readings that differ from the actual value of the characteristic being measured.
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From page 161... ...
· Long versus short reporting periods. In contrast with closed-end questions, open-end questions yield responses that are in respondents' own words, provide insights into respondents' frame of reference regarding the questions, are more detailed, and minimize the frames of reference imposed by the researcher.
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From page 162... ...
~ Implicit terms like soften" mean different things to different respondents and require more inference, whereas 'yesterday should have the same meaning to all respondents. Similarly, in the case of long versus short reporting periods, one should expect more accurate reporting about short and recent periods (e.g., yesterday or last week)
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From page 163... ...
Building on the results of methodological studies and more refined time-activity diary studies, one should be able to develop a concise inventory of exposure-related questions for a variety of contaminants to identify populations at risk. That should be done in conjunction with personal-monitoring studies, in which both short-term (diary)
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From page 164... ...
Of course, there is no guarantee that such monotonic relations will be found, and the extent of such statistical correlations needs to be empirically documented. INCORPORATING SURVEY-RESEARCH METHODS INTO EXPOSURE ASSESSMENT Exposure assessment should enlist the expertise of multidisciplinary teams of specialists including survey statisticians and field specialists.
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From page 165... ...
A series of small benchmark surveys of normal activity patterns or microenvironments would help to establish a basis for comparison in future exposure assessments by, for instance, defying healthy buildings for studies of the sickbuilding syndrome. Application of survey-research methods can also contribute to improving the effectiveness of exposure-study design.
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From page 166... ...
Three measurement approaches can be distinguished in population-based exposure assessments: direct, indirect, and questionnaire. In the direct approach, respondents report In time-use diaries and carry personal exposure monitors that record their exposures for short periods.
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From page 167... ...
· When the situations of high-exposure readings on personal monitors need to be identified more clearly, researchers should assess the feasibility and usefulness of having framed personnel observing respondents and collecting exposure data as unobtrusively as possible. Such a technique would require respondents' consent and selection of observation periods.
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