National Regression Results
| Parameter | Estimate | Std. Error | Parameter | Estimate | Std. Error |
|---|---|---|---|---|---|
| Const | 7.123*** | (0.207) | Secchi * MD | −0.259** | (0.085) |
| Secchia, b, c | 0.231*** | (0.034) | Secchi* ME | 2.428*** | (0.077) |
| Secchi * lake area demeanedc | 0.009* | (0.004) | Secchi * MI | −0.0680 | (0.048) |
| Secchi * < 150 m | 0.025** | (0.009) | Secchi * MO | 0.6730 | (0.739) |
| Secchi * lake distance | −0.034*** | (0.005) | Secchi * MT | −2.021*** | (0.465) |
| Secchi * urband | −0.0150 | (0.014) | Secchi * NC | −0.1830 | (0.123) |
| Secchi * ecoregion 5.2d | 0.075* | (0.036) | Secchi * ND | −0.2230 | (0.292) |
| Secchi * ecoregion 5.3 | 0.0430 | (0.033) | Secchi * NE | −0.1790 | (0.101) |
| Secchi * ecoregion 6.2 | 0.5940 | (0.462) | Secchi * NH | −0.0650 | (0.047) |
| Secchi * ecoregion 7.1 | 0.9910 | (0.596) | Secchi * NJ | −0.0030 | (0.052) |
| Secchi * ecoregion 8.2 | 0.0570 | (0.077) | Secchi * NY | −0.0740 | (0.04) |
| Secchi * ecoregion 8.3 | 0.0550 | (0.048) | Secchi * OH | −0.1980 | (0.16) |
| Secchi * ecoregion 8.4 | −0.0170 | (0.069) | Secchi * OK | −0.1240 | (0.266) |
| Secchi * ecoregion 8.5 | 0.0260 | (0.031) | Secchi * OR | −0.8670 | (0.525) |
| Secchi * ecoregion 9.2 | 0.150 | (0.1) | Secchi * PA | 0.154*** | (0.036) |
| Secchi * ecoregion 9.3 | 0.2230 | (0.201) | Secchi * RI | 0.102* | (0.047) |
| Secchi * ecoregion 9.4 | 0.2030 | (0.149) | Secchi * SC | −0.0530 | (0.084) |
| Secchi * ecoregion 10.2 | 0.3060 | (0.462) | Secchi * SD | −0.1270 | (0.287) |
| Secchi * ecoregion 11.1 | 0.6620 | (0.462) | Secchi * TN | −0.1130 | (0.078) |
| Secchi * ecoregion 13.1 | 0.3660 | (0.475) | Secchi * TX | −0.3930 | (0.233) |
| Secchi * ecoregion 15.4 | 0.0320 | (0.048) | Secchi * VA | −0.1340 | (0.083) |
| Secchi * ALd | 0.0030 | (0.202) | Secchi * VT | −0.0780 | (0.129) |
| Secchi * AR | 0.1210 | (0.15) | Secchi * WA | −0.9890 | (0.597) |
| Secchi * AZ | −0.3960 | (0.475) | Secchi * WI | −0.0330 | (0.08) |
| Secchi * CA | −0.7280 | (0.465) | < 150 m | 0.124*** | (0.009) |
| Secchi * CO | −0.4980 | (0.461) | Lake distance | −0.095*** | (0.005) |
| Secchi * CT | −0.266* | (0.12) | Lake areae | 0.013* | (0.005) |
| Secchi * DE | −0.0860 | (0.402) | Median income | 0.131*** | (0.014) |
| Secchi * FL | −0.0190 | (0.037) | Slope | 0.019*** | (0.002) |
| Secchi * GA | 0.0330 | (0.128) | Elevation | −0.0230 | (0.023) |
| Secchi * IA | −0.221* | (0.11) | Lot size | 0.101*** | (0.004) |
| Secchi * IL | −0.1070 | (0.08) | Building age | −0.125*** | (0.003) |
| Secchi * IN | 0.20 | (0.515) | Building size | 0.547*** | (0.01) |
| Secchi * KY | −1.956*** | (0.058) | Quarter 2 | 0.044*** | (0.002) |
| Secchi * LA | 0.0840 | (0.211) | Quarter 3 | 0.05*** | (0.002) |
| Secchi * MA | −0.0270 | (0.024) | Quarter 4 | 0.015*** | (0.002) |
Note: N = 485,860, standard errors clustered at tract level.
↵a Interaction terms for MN and ecoregion 8.1 were preselected as the excluded categories, because the area intersection contains the most observations in the sample.
↵b During estimation, interaction terms for KS, NM, WV, ecoregion 10.1, and ecoregion 12.1 were fully absorbed by fixed effects and dropped from model. Observations for ecoregion 12.1 all fall within AZ. Variation in estimates for KS, NM, and WV can be explained by the corresponding ecoregion interactions.
↵c The log of lake area is demeaned in the interaction term with Secchi. Thus, the Secchi coefficient alone can be interpreted as the effect of water quality for a lake with the mean log-lake area. Secchi * Lake area demeaned can be interpreted as the effect of an increase in lake size over the sample mean.
↵d Because this model is estimated with census tract by year fixed effects, it is not necessary to include urban, ecoregion, and state constituents as control variables.
↵e The lake area when not interacted with Secchi is not demeaned, as it only serves as a control variable in the model not a coefficient of interest.
↵* p < 0.005
↵** p < 0.01
↵*** p < 0.001.