You work in an outpatient substance use treatment program staffed by 2 case managers and 3 therapists, among others. Clients who participate do so for 3 months and attend multiple services including case management, individual therapy, and support groups. The program is designed to improve substance use outcomes (measured as number of days without substance use). You recently heard through the grapevine that clients have been expressing serious complaints about their experiences, including the times when services are to be delivered getting changed at the last minute and staff not seeming well-supported. As such, you set off to learn more about the experiences of clients so that you can make improvements. To do this, you stand at the front door one morning and ask those who enter whether they will participate in one of four focus groups you will be hosting. At the outset of the focus groups where you ask clients about their experiences, you also ask each participating client to complete a short survey that includes some questions on their basic demographics (age, gender, and racial/ethnic identity), what services they have participated in and with which staff, and their satisfaction with each of the services (scale of 1-5, 5 being very satisfied). You then proceed with the focus group for more information about their experiences.
Question: In this scenario, what kind of sampling was used in this evaluation?

none of these

random

snowball

stratified