TABLE 2.

Interventions and control groups.

References	Intervention	Comparison
Van der Wal and Kok (21)	- Laughter therapy with humor. - Laughter therapy without humor. - Laughter therapy, unknown whether humor was used.	All forms of control or comparison groups were allowed.
Zhao et al. (22)	- Laughter therapy. - Humor therapy. - Clown intervention.	Control groups received no specific humor or laughter intervention. Control conditions were for example: usual day care, placebo intervention.
Rudnick et al. (27)	- Stand-up comedy training (experimental arm). - Watching and discussing comedy videos (active control arm).	- Treatment as usual without any humor-related intervention (passive control arm).
Ventis et al. (28)	1. Systematic desensitization group (n = 13); rating non-humorous hierarchy items for fear, standard desensitization procedure. 2. Humor desensitization group (n = 14); rating non-humorous hierarchy items for fear, eliciting humorous perspective, completing incomplete statements about spiders in a humorous way.	- Control group (n = 12); no treatment. Waiting list condition.
Deutsch (29)	3 types of audiovisual stimuli: 1. “Static”: 10-min static signal, complete with white noise. 2. A nature documentary: this film was to provide interesting material for the subjects without being specifically humorous. 3. A comedy clip: a 10-min portion of a Seinfeld episode. - Each segment was 10 min long, divided into 2, 5-min segments, and viewed in 10 s increments. - Segments were run on individual basis to prevent group effects. - All subjects watched the 3 films in the order: nature documentary, comedy, static video.	- The static video was the control condition for the content-based formats of the other two conditions.
Cai et al. (17)	- n = 15 - Humor skill development program based on the 8 steps program by McGhee (37). - 5 weeks of training with 2 sessions a week.	- n = 15 - Doing handwork
Gelkopf et al. (26)	- The experimental group watched films labeled as comedies, such as Laurel and Hardy, Charlie Chaplin, Tootsie, and Police Academy. - During 3 months, daily 2 films, 4 days of the week.	- The control group watched neutral films (action, romantic, drama) and also some comedies (only 15% of the films). - During 3 months, daily 2 films, 4 days of the week.
O’Brien (10)	- 10 therapists treated 2 participants: 1 participant in the experimental condition, 1 in the control condition. - Humor defined as a verbal behavior with the elements of SLAP. Therapists were to remember the elements of humor for use in session and increasing the frequency with which comments containing SLAP were made. - Brief counseling was offered, limited to four sessions.	- Restricting the use of humor, therapists were to limit comments containing SLAP. - Brief counseling was offered, limited to four sessions.
Panichelli et al. (25)	- No interventions were designed to be applied. Humorous interventions were scored in retrospect. - Spontaneous humor was allowed during the sessions, but aggressive humor was avoided to protect the therapeutic alliance. - Humorous interventions were used only if clinically appropriate. - Various humorous interventions were used: * Exaggeration of the client’s ideas and behavior. * Expressing non-verbalized or implicit client thoughts. * Asking about the client’s favorite joke. * Using jokes and metaphors. * Giving a humorous, provocative nickname. - Sessions have been conducted by 1 therapist, the author of the study.	- No control
Falkenberg et al. (16)	- Humor training program McGhee.	- No control.