Table 3 Session format

Effective

Collins 2006 [25]

16-weeks

16 classes

2 h

Group

In person

Creswell 2012 [26]

8-weeks

8 sessions + 1 retreat

120-minute sessions. Day-long retreat

Group

In person

Gaggioli 2014 [30]

3-weeks

3 sessions

2 h

Group

In person

Larsson 2016 [38]

34-weeks

Between 2–5 group and 1–16 individual meetings

Maximum 1.5 h

Individual and/or group

In person and/or online

Ehlers 2017 [27]

24-weeks

72 sessions

1-hour

Group

In person

Bouwman 2017 [22]

6-weeks

NR

NR

Individual

Online

Cohen-Mansfield 2018 [24]

NR

Mean 4 [range 0–7] group sessions,

mean 5 [range 1–13] individual meetings

NR

Individual and/or group

In person

Hwang 2019 [32]

12-weeks

24 sessions

2 h 35 min

Group

In person

Kall 2020 [33]

8-weeks

8 modules

NR

Individual

Online

Ghanbari 2021 [31]

4-weeks

16 sessions

30 min

NR

In person

Fong 2021 [29]

1 day

1 event

NR

Individual and/or group

In person and/or online

Kall 2021* [34]

9-weeks

9 modules

NR

Individual

Online

Nazari 2021 [39]

5-weeks

5 sessions

60–80 min

Group

In person

Kotwal 2021 [36]

Between 6- and 24-months

NR

NR

Individual and/or group

In person

Can’t tell if effective

Steven 2000 [43]

NR

12 lessons

NR

Group

In person

Rolandi 2020 [40]

5.5-weeks

5 sessions + 6 tutoring

2 hours^φ

Group

In person

Caputi 2021 [23]

5-weeks

5 sessions

50-minutes

Group

In person

Kanter 2021 [35]

16 days

14 text messages

Between 5 and 12 min

Individual

Online, mobile based

Shapira 2021 [42]

3.5-weeks

7 sessions

1-1.5 h

Group

Online

Not effective

Fields 2021 [28]

8-weeks

8 sessions

NR

Individual

Online

Sandu 2021 [41]

1 year

NR

Median 11-minute phone call

Individual

Over the phone

Kramer 2022 [37]

NR

NR

NR

Individual

Online