Table 1 Characteristics of group 1~4
| Â | knowledge | concern | dummy variable | Number | |
|---|---|---|---|---|---|
| Â | Â | Â | Â | 18-month group | 36-month group |
Group 1 | high | Low | Â | 690 | 748 |
Group 2 | low | Low | X1 | 1145 | 813 |
Group 3 | high | high | X2 | 367 | 379 |
Group 4 | low | high | X3 | 418 | 306 |
| Â | knowledge | concern | dummy variable | Number | |
|---|---|---|---|---|---|
| Â | Â | Â | Â | 18-month group | 36-month group |
Group 1 | high | Low | Â | 690 | 748 |
Group 2 | low | Low | X1 | 1145 | 813 |
Group 3 | high | high | X2 | 367 | 379 |
Group 4 | low | high | X3 | 418 | 306 |