What type of sampling is the study below. Provide an analysis and the advantages and disadvantages of this approach:
Six hundred and sixty-two divorced individuals from Germany, Italy, and Switzerland participated in this study, including 282 German subjects (228 women and 54 men), 141 Italian subjects (85 women and 56 men), and 239 Swiss subjects (81 women and 158 men). All participants selected for analysis had at least one child, so all participants experienced this particular stress. Participants in Germany and Italy were recruited via newspaper advertisements (in Milan and Berlin), while participants in Switzerland were recruited nationwide via newspapers and an internet site. (Use of the Internet to recruit Swiss participants probably accounts for the higher proportion of men in this subgroup.) There were no differences between subjects responding via mailed questionnaires versus the Internet.