Pilot survey implementation Statistical results

Table 1 Disposition of initial contacts and response rates Number Percentage Category Letters mailed 462 100 89 19.3 Moved out of area, undeliver- able 373 81 Net sample size 18.8 87 No answer after repeated calls Sample contacted 286 62 Ineligible due to illness, lan- 11.7 54 guage 131 28.4 Refusals no time, lack of trust, etc. 5 5 No shows 96 Accepted and interviewed 41.4 Response rate of those con- tacted and eligible 33.6 Response rate of those con- tacted 25.7 Response rate of net sample near the river and towns along the river Fort Lupton, Fort Morgan, Greeley, Longmont, and Platteville. To increase the chances for a com- pleted interview, we reminded the participants with a phone call shortly before the interview. As a result, only five people or 5 failed to show for the interview. Two individuals conducted the in- terviews in the respondent’s home. 1 The disposi- tion of these mailings is indicated in Table 1 along with three different estimates of the response rate. Depending on whether one calculates the response rate on just those that were contacted by phone or all residents, the response rate varies from a low of 25.7 to a high of 41. The low response rate is due in part to losing some individuals at each of the many contacts made. While the low response rate does not influence the illustration of how we portrayed ecosystem services, it certainly has im- plications for generalizing the dollar value of re- sults to the population. We address the implications of this low response rate in the later section. Table 2 presents the number and percent ‘yes’ responses at each bid amount. As can be seen it is a fairly, although not perfectly, well behaved dis- tribution. At the two lowest dollar amounts, 100 indicated they would pay. With the exception of three bid amounts, the percentage of ‘yes’ re- sponses decrease as the bid increases. It is not perfectly monotonic, but some of this is more than likely due to the small sample sizes in the individual cells. independent variables times their respective means. Confidence intervals around mean WTP were calculated using the variance-covariance ma- trix and a simulation approach of Park et al. 1991.

12. Pilot survey implementation

Sufficient funds were available to allow for a small sample using in-person interviews of about 100 individuals during the spring and summer of 1998. The sample frame were individuals living in towns nearby or along the portions of the South Platte river under study. From February to July 1998, we mailed 462 introductory letters to house- holds in the South Platte river basin in the follow- ing locations: two suburbs of northern Denver 1 While two interviewers were used, we tested whether this resulted in different responses. Using a dummy variable in the logit regression of WTP we found no statistically significant effect. Table 2 Responses at each bid amount 3 2 1 100 Bid 50 40 30 20 12 10 8 5 5 4 2 3 1 11 Yes 9 8 9 5 3 No 3 4 8 4 3 5 5 1 2 50 33 50 63 38 50 90 Yes 80 100 100

13. Statistical results

A full statistical model including all survey demographic and attitude variables was initially estimated. To conserve space, only the model with independent variables significant at the 0.05 level or better were retained. Demographic variables such as income, education or age were consis- tently insignificant and these were not included in the final model. The final statistical model was: [logyes1 − yes] = B o − B 1 bid − B 2 unlimited water + B 3 government purchase + B 4 environmentalist − B 5 average water bill + B 6 urban 3 where ‘yes’ is the dependent variable and records if a person was or wasn’t willing to pay the amount asked during the interview. The number 1 records a yes vote, and 0 records a no vote. Bid, specifies the increase in water bill the per- son was asked to pay. Unlimited water, ‘do you agree or disagree with the statement; farmers should be allowed to use as much water as they are entitled to even if it temporarily dries up portions of streams?’ agree, 1 and disagree, 0. Government purchase: ‘do you agree or dis- agree with the statement; Government purchase of land along the South Platte river to increase fish and wildlife is something I would support?’ agree, 1 and disagree, 0. Environmentalist: are you a member of a con- servation or environmental organization? yes, 1 and no, 0. Average water bill: the average indoor use monthly water bill for each community. Urban equals one if lives in urbansuburban area, equals zero if live in ruralfarm area.

14. Interpretation of the regression results