Introduction

Given the considerable public concern about possible health risks from exposure to power frequency electric and magnetic fields, what kinds of exposure controls would members of the public select on the basis of their current knowledge and beliefs? The answer might be expected to depend upon the costs of exposure controls, the extent to which people are familiar with the state of the evidence, and the extent to which they consider risks from field exposure plausible.

This paper reports the results of a study using a survey instrument to present 40 options to reduce or eliminate exposure to fields from 60-Hz electric power to an opportunity sample of adults from the Pittsburgh area. The respondents can be reasonably characterized as "middle income, lay opinion leaders," i.e, they have a somewhat higher level of education and are somewhat more likely to be involved in leadership positions than the general public. The exposure control options ranged from voluntary design, measurement and information guidelines to banning sources of high or unusual fields. Respondents rated the options as "should definitely be done," "uncertain," or "should definitely not be done." Additionally, all subjects rated their degree of belief in health effects. A majority of subjects favored implementing twelve of the options proposed. These twelve options are characterized by restrictions on new sources of high fields, including overhead distribution and transmission lines and wiring in new buildings, and providing field information on new appliances. Surprisingly, asking respondents to estimate the costs had no significant overall effect on preferences for exposure control options, although the cost estimates produced tended to be reasonable. Insensitivity to the fact that field strength decreases with distance was approximately equally prevalent in this study as in a previous study of lay perceptions of fields.1 Although most subjects were moderate in their beliefs (less than 10% thought that serious health effects from exposure to electric and magnetic fields were "unbelievable" or "not only believable, but true"), stronger beliefs in health effects correlated positively with preferences for implementing more exposure reduction strategies. Overall, subjects appeared to favor field limitation measures that could entail significant investments, especially for new sources.

Study Design

Subjects were divided into two treatments, no-cost and cost. In the first, subjects completed a questionnaire that asked for their preferences regarding the implementation of field-exposure control. In the cost condition, the questionnaire included additional questions requesting estimates of the costs of twelve of the field control measures. A small portion of both groups of respondents also received an informational brochure32 on 60-Hz fields. The questionnaire was piloted on a half-dozen subjects and subsequently shortened, so that the no-cost version took approximately twenty minutes to complete.

Figure 1
Instructions for using the response scale
[Omitted]

The questionnaire was divided into six sections. The first section consisted of two questions about prior knowledge of fields, and one that asked subjects to judge the plausibility of human health risks from exposure to fields. These were followed by an explanation of how to use the response scale. Figure 1 includes this explanation.

The questions in sections two through five asked subjects if they thought each of 40 field control options should be implemented. Fields from transmission lines, distribution lines, building wiring and appliances were covered in these four sections, respectively. Figure 2 illustrates the questions for one option, together with the associated cost-estimation task that was included in the cost condition.

Figure 2

Sample questionnaire item including field reduction item (above)

and cost-estimation task for respondents in cost condition (below)

[deleted]

Abbreviated descriptions of each of the options are provided in the right-hand column of Figure 3. In each section, questions were ordered roughly from options requiring the least intervention (e.g., issuing voluntary guidelines to the industry for low-field appliance design) to those requiring the most (e.g., banning all further sales of electrical appliances until manufacturers can reduce the field exposure they produce). The problem of defining "exposure"3 was not discussed. The options can be characterized by whether the changes suggested focus on the dissemination of information and are not mandatory for the public (i.e., information strategies), are mandatory, affect previously established field-exposure conditions (i.e., strategies that involve retrofitting), or require a total shutdown (i.e., ban strategies). Demographic questions concluded the questionnaire.

Figure 3 --/4

Responses to field-exposure reduction and elimination options

[deleted]

The field control options used can be classified into four general categories: those that focus on information dissemination and are not mandatory (I); those that specify some mandatory action but do not require retrofitting existing facilities (M); those that involve retrofit of existing facilities (R); and those that involve a ban on a product or activity (B). Each field-exposure control option was independently coded into one of the four strategies by two coders. The independent codings agreed on 38 of the 40 options, and the disagreements were resolved. The codings are shown in the center column of Figure 3.

Subjects

Questionnaires were distributed during the Fall of 1990 to an opportunity sample of adults whose children were members of the Fox Chapel Hockey Club, to adults who were members of the Pittsburgh Association of Society Executives, and several friends and associates identified by both groups. The sample could be described as "white and middle income." The parents of Hockey Club members have heterogeneous careers. They are on average better educated than the average U.S. citizen and more likely to be involved in executive or other leadership positions, but they come from several communities with varied incomes. Many are involved in community activities. The members of the Pittsburgh Association of Society Executives are similar, although all are employed in semi-technical administrative positions. These groups were chosen as convenience samples of typical "community opinion leaders," the sorts of reasonably well-educated, active people to whom others might turn for advice and community leadership in the event of a controversy over power line siting. We gave $8.00 to the club for each completed response received, all of which were usable. Table 1 characterizes the sample. The majority of respondents (65%) had completed an undergraduate college education and about half (53%) were female. Most were homeowners, and most did not consider themselves technically minded. The sample can reasonably be characterized as consisting of "lay opinion leaders."

Table 1
Demographics of Respondents [Omitted]

The use of such opportunity samples is rather common practice in studies of risk perception,5 particularly when the objective is to study inferences about risk rather than to sample well formulated beliefs. In previous research on public understanding of the physics of fields,6 very similar results were found in opportunity samples and a true random sample, although a small effect from the higher educational level of the opportunity sample was observed.

Results

Of 425 questionnaires distributed, 199 (47%) were returned, all usable. The response rate varied by condition, with lower returns on more time consuming tasks. On the basis of discussion with the leader of the two groups, we have no reason to believe that the attributes of the non-respondents were significantly different than those of the respondents, with the one exception that respondents were probably more interested in the topic. Of those involving the no information condition, 94 (62% of the 152 distributed) were returned in the no-cost condition and 81 (52% of 156) were returned in the cost condition. Response rates were much lower in the information condition. Six (17% of the 35 distributed) were returned in the no-cost condition and eighteen (22% of 82) were returned in the cost condition. Although those who received the brochure appear slightly less likely to say that any given option should be implemented, differences are not statistically significant (t = -1.38, p = 0.17). Given the low response rate for the information treatment group, no further separate analysis of these data was undertaken. Responses were judged to be sufficiently similar to justify combining the information and no information conditions in the subsequent analyses of preferences for exposure control options.

Most respondents (83%) had heard of electric and magnetic fields. This information came primarily from respondents' general education or the news media (i.e., television, newspapers, magazines). A majority (66%) had also heard of the possibility of health effects from exposure to fields. Of those who had heard of fields, 84% found human health risks believable, compared to only 75% of those who had not heard of fields. Of those who had heard of the possibility of health effects from exposure to fields, 89% found human health risks from exposure to fields believable, compared to only 70% of who hadn't. It is interesting to compare these results with responses to a 1990 survey commissioned by Edison Electric Institute.7 In a nationally representative sample, 38% had recently heard something about environmental effects of electric and magnetic fields, and 35% reported hearing about health or environmental hazards associated with transmission and distribution lines. It seems likely that the difference between our sample and the EEI sample reflects three factors: the greater amount of information we were able to provide to our sample respondents, the higher education level of our sample, and the fact that because they were self-selected, our respondents probably had more interest in the topic.

Analyses of the effects of the experimental conditions and of differences in preferences related to education and gender are followed by exploration of the relationship between beliefs in health effects and preferences for field-exposure reduction or elimination.

Cost Estimates

Respondents in the cost condition were asked to estimate costs for nine different options,8 involving a total of twelve different estimates. For each such estimate, subjects were asked to respond as if "the option were implemented everywhere in the U.S. and the costs were somehow spread equally across all electric power consumers in the U.S." Costs were framed in terms that would be most relevant to the respondents. For example, respondents were asked to estimate costs of power line controls in terms of the amount of average annual increase in the respondents' electric bill over the next few years for implementing the option. To illustrate, the first option cost-condition respondents were asked to estimate by cost was doubling the right-of-way for all new transmission lines. The expert estimate for an upper bound on the cost of this option was $9 a year. Subjects were given a choice between six ranges: "less than $5 per year," "between $5 and $10 per year," "between $10 and $50 per year," "between $50 and $100 per year," "between $100 and $500 per year," and "more than $500 per year." The mean, median and modal responses for this option coincided at "between $10 and $50 per year," which is the next response category higher than the highest spanned by the expert estimate.

Relative to an expert estimate of these costs, the median and modal lay estimates fell in the correct interval for eight and seven of the options, respectively. Median lay estimates were one or two response categories higher than the range spanned by the expert estimate for three of the thirteen options. Although this illustrates a slight tendency to overestimate the costs, given the numerous uncertainties in estimating such costs, subjects responded with relatively realistic estimates. Details of the lay cost estimates are provided in Appendix I.

Effects of the Cost-Estimation Task on Preferences

Explicit consideration of costs was hypothesized to dampen preferences for implementing field reduction or elimination options by bringing budget constraints to mind. A simple comparison of the proportions of subjects who preferred to implement each option by cost condition shows the proportions to be similar on all options. Where they differ, differences are small, and the proportions are sometimes greater for the cost condition (e.g., 28% of the cost and 22% of the no-cost respondents favored forbidding access to rights-of-way for only new transmission lines) and sometimes greater for the no-cost condition (e.g., 24% of the cost and 26% of no-cost favored forbidding access to rights-of-way for all new and existing transmission lines).

A simple regression of the proportions of those preferring to implement each option in the cost condition on the proportions of those in the no-cost condition shows that the proportions are highly correlated (R2 = 0.96), the constant is indistinguishable from zero (t = 1.06, df = 39) and the regression coefficient is highly significant and indistinguishable from one (

= 1.0, t = 31.10, p < 0.001). The regression was actually performed on the arc sine square root transformations of the proportions, to meet the standard regression assumptions. By chance, a much larger proportion of women respondents were in the no-cost than in the cost condition, but there is no difference by cost condition controlling for gender. Given that the cost-estimation task had no detectable effect on expressed preferences, the cost and no-cost conditions are combined in the following analyses.

Comments on the questionnaire indicated that subjects in the no-cost condition were cognizant of the importance of considering costs. Of the 21 subjects in the no-cost condition who wrote comments on the questionnaire, one-third mentioned cost. This may partially explain the similarity between the two groups. Other possibilities are that subjects' priors are higher than actual costs, which the cost-estimation task helped them approach, or that the cost-estimation task design did not effectively increase subjects' attention to costs.

Overall Preferences

Most options were unsupported by the majority of respondents, but some strategies were consistently supported across the four exposure domains. Figure 3 summarizes the pooled results for all options.

Expanding or managing the use of rights-of-way would be an inexpensive way to reduce exposure. However, of these options, only limiting use of rights-of-way (51%) and doubling rights-of-way (64%) under new transmission lines were favored by a majority of the respondents. Yet, a majority would bury new transmission lines (58%) and new urban distribution lines (64%). Consistent with observations in previous studies,9 new lines are consistently treated differently. This is illustrated by the smaller proportion of respondents who favor doubling rights-of-way under existing lines (22%), burying existing urban overhead transmission (29%), and burying distribution lines (30%) (see Figure 3). Many respondents did, however, comment on the desirability of longer time spans for retrofitting. The questionnaire suggested that five years be allowed for addressing existing conditions, whereas some respondents wrote comments suggesting that ten to twenty years would be more appropriate. For example, one respondent wrote: "Five years is too short a compliance term. I would have voted for some of the changes if existing facilities had 15 years to comply."

By examining the percentages of subjects preferring to implement double width rights-of-way (ROW), optional property purchase at up to three times ROW, and optional property purchase within sight of the line, one can see that approximately 20% of respondents were insensitive to the way in which field strength changes with distance from the line. This is roughly consistent with the findings from previous investigations of lay perceptions of fields,10 showing lay people tend to substantially underestimate the rate at which field strength declines with distance. It is an open question whether education about how field strength declines with distance would change these preferences.

Respondents generally favored new low-field designs, where they were suggested. Seventy-one percent favored new low-field designs for distribution lines. A majority (61%) would also like to see sales of low-field and trade-ins of high-field appliances encouraged.

The informational strategies represented in the first few wiring and appliance options are also very popular. Most respondents want to see voluntary measurements of fields from wiring in building and houses (88%), voluntary wiring (88%) and appliance design (89%) guidelines, and voluntary appliance labeling (84%). Slightly fewer would like to see required building codes for wiring in all new buildings (72%), required measurements of fields from wiring at point of sale (61%), and required appliance labeling (81%). Several respondents mentioned that they would like to see more insulation and shielding strategies. For example, one wrote "What about shielded cables? What engineering studies have been done on how to reduce levels?"

Given the choice between increasing research efforts to find out "exactly what health risks there may be from electric and magnetic fields" or immediately taking "strong action to reduce exposure to electric and magnetic fields even if it means higher electric rates," only 18% of a nationally representative sample choose immediate strong action,11 up from 11% in 1987. This could relate to how people interpreted "strong action." Very few respondents chose the ban options in any domain, showing they were careful to reject extreme strategies (see Figures 3 and 5). Nevertheless, a majority of respondents in our survey endorse a number of field control actions now, including giving the public more information about fields, low-field designs, and burying transmission and distribution lines. Consistent with this, the 1991 EEI survey also showed that 61% of people polled favor regulation of fields from transmission lines, up from 51% in 1987.

Individual Differences in Overall Field-Control Preferences

Previous research has sometimes shown that women are more concerned about environmental risks than men,12 for which reason we expected women to favor field-exposure reduction or elimination on average more than men. Technical-mindedness, which was self-reported, was expected to correspond to a pro-technology attitude, and hence a weaker preference for field-exposure controls. Table 2 shows the proportion in favor of each kind of field-exposure control strategy, averaged across the options categorized as that kind of strategy. While there is little difference between technically and non-technically-minded women, men are on average less inclined to favor all strategies than women, and non-technically minded men somewhat more likely to favor most strategies than technically-minded men. These general tendencies appear even when controlling for beliefs in health effects.

Table 2
Percent age of respondents favoring field-exposure reduction strategies

by gender and self-judged technical-mindedness [Omitted]

Belief in Human Health Risks from Exposure to Fields

The question on degree of belief in health effects was worded thus:

How plausible do you think it is that exposure to the electric and magnetic fields from electric power poses a serious human health risk that is, does this idea seem believable to you, does it seem to make sense?

Subjects were given a response choice of "unbelievable, the idea that electric and magnetic fields might cause serious human health risks just doesn't make any sense at all to me," "somewhat unbelievable, the idea that electric and magnetic fields might cause serious human health risks does not make much sense to me," "somewhat believable, the idea that electric and magnetic fields might cause serious human health risks does make some sense to me," "believable, the idea that electric and magnetic fields might cause serious health risks makes a lot of sense to me," and "not only believable, but true, I am fairly certain that electric and magnetic fields actually do cause serious human health risks." Again, strong beliefs in risks could be expected to correlate with stronger preferences for exposure control.

Figure 4 shows the distribution of beliefs in health effects by gender and by technical-mindedness. More people find health effects believable than not. As Figure 4 also shows, women tend to find effects from exposure more believable than men. Several respondents spontaneously mentioned the lack of knowledge about possible risks from fields. Their comments indicate that at least some are sensitive to the degree of scientific uncertainty about health risks from fields. One respondent wrote "Need more studies on health effects from exposure." Another said, "It is not clear what type of damage occurs from these lines (if any)." A third wrote "A risk factor has not been determined. Let's not go crazy trying to control an unknown risk."

Figure 4

Degree of belief in human health risk from exposure to

60-Hz electric and magnetic fields

[deleted]

How, and to what extent, does a respondent's prior beliefs about possible risks from exposure effect the exposure options they prefer? The answer, is that stronger beliefs in health effects are consistently associated with a stronger preference for implementing a given field-exposure control option. However, across the four general strategies, retrofits are less popular than prospective mandatory controls. Finally, no group shows significant support for strategies that involve bans.

Reaching these conclusions required a statistical analysis that uses Bayesian updating procedures, but the details can be skipped by non-technical readers. The analytical results, in the form of posterior distributions of preferences for exposure control (0 = don't control, 1 = do control) are shown in Figure 5 by degree of belief in effects from fields, and by strategy. These probability density functions are calculated assuming a uniform [i.e., "uninformative," beta (1,1)] prior distribution. An updating procedure incorporates the data, as illustrated in the equations below.13 xi is an individual's choice to implement a specific option (1 = do; 0, otherwise). [Mathematical symbols cannot be reproduced as ascii text.]

Table 3
Example of posterior distribution for the strategy:
Forbid all NEW overhead lines, build underground [Omitted]

Figure 5
Posterior distributions for respondents' preferences for control options, by health effects belief and strategy type. Curves indicates results for a prior belief that health effects from fields are unbelievable or somewhat unbelievable, somewhat believable, or believable or true [Omitted]

Figure 5 illustrates the posterior distributions across all options for each strategy, by belief in human health risks from fields. The calculation of these distributions by strategy treats an individual's responses to each option of that strategy type as independent. Although this assumption may seem strong, options differ in many regards (e.g., source of fields, type of action proposed, proposed actor, cost). These specifics, like the specifics of a referendum, may cause individuals to assess various options from the same strategy differently, despite the individual's general level of preference for that type of strategy. For comparison, the distributions for a single option from each of the four strategies are also shown.

Discussion

Power frequency electric and magnetic fields have recently received much media attention. This is due undoubtedly to advances in the science of fields as well as to changes in lay perceptions of fields. Regardless of the cause, lay preferences for field-exposure reduction or elimination are also increasing in importance and can be expected to play an increasingly central role in regulatory and management choices involving exposure reduction as well as in litigation.

Preferences expressed in this study show that our sample of lay opinion leaders is willing to endorse even potentially costly options for field-exposure reduction or elimination. Information oriented exposure reduction options were generally preferred by most respondents, regardless of their degree of belief in health effects from exposure to fields. New lines and wiring were treated differently from those already existing. Hence adding retrofitting to an option, such as doubling the right-of-way for old as well as new transmission lines, reduced preferences for the option. Bans were generally eschewed by respondents. On average, women favored field controls more than men, and non-technically-minded men more than technically-minded men. Such differences may increase the likelihood that some social groups will have trouble comprehending others' attitudes toward field control. Common misconceptions, such as underestimating how fast field strength drops off with distance, may affect the kinds of policies people request or endorse. The strong association between beliefs in human health effects and preferences for field-exposure control implies that if people have misconceptions about health effects,14 those are also likely to affect their preferences. Future work on the relationship between preferences, knowledge, and attributes of specific field-exposure controls should further clarify what various interest groups pay attention to, and why.

Because these results are from an opportunity sample, care must be exercised in extrapolating them to other settings. As citizens become more aware of the topic, previous studies we have completed suggest that their level of concern is likely to increase.15 In addition, people in settings that involve actual controversies over facilities citing are likely to favor greater levels of field-exposure control. Both of these considerations suggest that, if they contain a systematic bias, the results reported here may underestimate the level of field-exposure control that the public will desire in many settings

[Appendices I & II are in tabular form and have been deleted]

Notes

* The authors thank Erin Allerton, Paul Fischbeck, Keith Florig, Gordon Hester, Darlene Stangl, Patti Steranchak & Lisa Stanziale for assistance or advice in the execution of the work and preparation of this paper and William Hakanson, the Fox Chapel Hockey Club and the Pittsburgh Association of Society Executives for providing subjects. The research was supported by the Electrical Power Research Institute under RP 2955-3. The authors are solely responsible for the contents.

** Dr. Bostrum is Assistant Professor of Public Policy at the School of Public Policy, Georgia Institute of Technology. She received her B.A. (English) from the University of Washington, her M.B.A. from Western Washington University and her Ph.D. (Public Policy Analysis) from Carnegie Mellon University.

Dr. Morgan is Professor and Head of the Department of Engineering and Public Policy, Carnegie Mellon University (DEPP-CMU) He received his B.A. (Physics) from Harvard College, his M.S. (Astronomy & Space Science) from Cornell University and his Ph.D. (Applied Physics and Information Science) from the University of California, San Diego.

Dr. Adams is Research Engineer at the DEPP-CMU. He received his B.S. (Physics) from the University of Massachusetts, Boston and his M.S. and Ph.D. (Electrical & Computer Engineering) from the University of Massachusetts, Amherst.

Dr. Nair is Associate Professor and Associate Department Head at the DEPP-CMU. She received her B.Sc. (Physics & Mathematics) and M.Sc. (Physics) from the University of Bombay, M.S. (Physics) from Kansas State University and Ph.D. (Physics) from Northwestern University.

1 See, e.g., Electromagnetic Fields, Consumer Reports, May 1994, at 354, 355.

2 M. Granger Morgan, Electric and Magnetic Fields from 60 Hertz Electric Power: What do we know about possible health risks? (DEPP-CMU 1989).

3 M. Granger Morgan & Indira Nair, Alternative Functional Relationships Between ELF Field Exposure and Possible Health Effects: Report on an Expert Workshop, 13 Bioelectromagnetics 335 (1992).

4 (N=199). ROW = right-of-way, I = information strategy, M = mandatory, R = retrofit, B = ban. *Included cost task.

5 Sarah Lichtenstein et al., Judged Frequency of Lethal Events, 4 J. Exp. Psych.: Hum. Learning & Memory, 551 (1978). Donald G. MacGregor, Worry about Technical Activities and Life Concerns, 11 Risk Anal. 315 (1991).

6 M. Granger Morgan et al., Lay Understanding of Low-Frequency Electric and Magnetic Fields, 11 Bioelectromagnetics 313 (1990).

7 Edison Electric Institute, Quarterly Public Opinion Review: American Attitudes toward Major Issues Facing the Electrical Utility Industry, EMF -- Pts I & II, 1st Quarter (1991).

8 See starred options in Figure 3; see also Appendix I (Responses to All Cost Questions) and II (Summary of Cost Calculations).

9 Gordon Hester et al., Small Group Studies of Regulatory Decision-Making for Power-Frequency Electric and Magnetic Fields, 10 Risk Anal. 213 (1990).

10 Morgan et al., supra note 6.

11 Edison Electric Institute, supra note 7.

12 Thomas A. Arcury, Susan J. Scollay & Timothy P. Johnson, Sex Differences in Environmental Concern and Knowledge: The Case of Acid Rain, 9/10 Sex Roles 463 (1987); T. Jean Blocker & Douglas L. Eckberg, Environmental Issues as Women's Issues: General Concerns and Local Hazards, 70 Soc. Sci. Q. 586 (1989); Gregory W. Fischer et al., What Risks Are People Concerned About? 11 Risk Anal. 303 (1991).

13 Morris H. DeGroot, Optimal Statistical Decisions (1970).

14 Morgan et al., supra note 6.

15 Donald G. MacGregor, Paul Slovic & M. Granger Morgan, Perception of Risks from Electromagnetic Fields: A Psychometric Evaluation of a Risk-communication Approach, Risk Anal. (in press).