1 Subjects: “...Disease Notification...”

2 “...This paper studies the effects of a voluntary skill certification scheme in an online freelancing...”

3 Subjects: “...disease notification...”

4 Subjects: “...notification...”

5 Subjects: “...certification...”

6 Subjects: “...certification mark...”

7 Subjects: “...death certificates...”

8 Subjects: “...energy performance certificates...”

9 “... certification for absence from work from 1948 to 2010, it shows that doctors, employers, employees, politicians...”