Systematic review: The placebo effect of psychological interventions in the treatment of irritable bowel syndrome

Table 1 Descriptive statistics for characteristics of included studies

Ref.	Year	Country	n	Mean age (yr)	Female sex	Recruitment	Years of illness	Criteria	Therapy	Control	Format	Ses-sions	Trained therapist intervention/placebo	Protocol inter-vention/placebo
Craske et al[23] 2011	2011	United States	110	39.4	74	Community advertisement; university clinic		RII	Cognitive-behavior-al therapy	Psycho-educatio-nal support	Individual	10	Unclear/unclear	Yes/yes
Drossman et al[24] 2003	2003	United States and Canada	215	37.3	100	Community and hospital advertisement; physician referral in community or university-based practices		R1	Cognitive-behavior-al therapy	Psycho-educational support	Unclear	12	Yes/yes	Yes/yes
Gaylord et al[25] 2011	2011	United States	75	42.7	100	Local advertisement; physician care		RII	Mindful-ness	Support	Group	9	Yes/yes	Yes/yes
Moser et al[26] 2013	2013	Austria	100	45.5	79	Primary, secondary care and university clinic	4/10.5	RIII	Hypno-therapy	Support	Group	10	Yes/yes	Yes/no
Payne et al[27] 1995	1995	United States	34	40.1	85	Personal physician	16	RI	Cognitive therapy	Psycho-educatio-nal support	Therapy: individual; Control: group	10	Yes/unclear	Yes/yes
Shinozaki[28] 2010	2010	Japan	21	31.6	52	University clinic			Relax	Psycho-educatio-nal support	Individual	8	Yes/unclear	Yes/yes

Table 2 Risk of bias ratings for included studies

Ref.	Year	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Dropout treatment/placebo control (%)	ITT or PP
Craske et al[23] 2011	2011	Low	Low	Low	Low	Low	Low	Interoceptive Exposure:34; Stress Management: 36/16	ITT
Drossman et al[24] 2003	2003	Low	Low	Low	Low	Low	Low	13/24	ITT
Gaylord et al[25] 2011	2011	Low	Low	Low	Low	Low	Low	6/18	ITT
Moser et al[26] 2013	2013	Low	Low	Low	Low	Low	Low	0/2	PP
Payne et al[27] 1995	1995	Unclear	Unclear	Low	Unclear	Low	Low	0/0	ITT
Shinozaki[28] 2010	2010	Unclear	Unclear	High	High	Low	Low	0/0	ITT

Possible ratings were low, high or unclear risk of bias. Studies with 2 control groups were rated twice for risk of bias because of lack of blinding (rated or active control groups appear in parentheses). ITT indicates that the analysis was intent-to-treat (analyzed as randomized). PP: Per protocol.

Table 3 Placebo treatment and placebo response rate

Ref.	Placebo treatment	Primary outcome measure	Duration of treatment1	Follow-up	Placebo response	Treatment response
Craske et al[23] 2011	Psycho-educational support	BSS index	10 wk	3 mo	59% (13/22)	62% (29/47)1
						54% (22/41)2
Drossman et al[24] 2003	Psycho-educational support	Composite score3	12 wk		37.3% (19/51)	70% (77/110)
Gaylord et al[25] 2011	Support group	IBS-SSS	8 wk	3 mo	45.2% (17.6/39)	68.8% (27.4/36)
					53.1% (20.7/39)	75% (27/36)
Moser et al[26] 2013	Supportive talks	IBS-IS	12 wk	12 mo	40.9%( 18/44)	60.8%(28/46)
					25% (11/44)	54.3% (25/46)
Payne et al[27] 1995	Psycho-educational support	CPSR	8 wk	3 mo	25% (3/12)	75% (9/12)
					18% (2/12)	83% (10/12)
Shinozaki[28] 2010	Psycho-educational support	AR	8 wk		30% (3/10)	81.8% (9/11)

¹Cognitive behavioral treatment;

²Stress management;

³Composite score: Mc-Gill Pain Questionnaire; IBS-QOL; satisfaction with treatment; global well-being. IBS: Irritable bowel syndrome; BSS: Bowel syndrome severity index; IBS-SSS: IBS-Symptom Severity Score; IBS-IS: IBS-Impact Scale; AR: Adequate relief; CPSR: Composite primary symptom reduction.

Table 4 Comparison of outcome measurements

Author	Symptoms	Anxiety	Depression	Quality of life
Craske CBT-IE	Bowel Symptom Severity (BSS)	VSI	-	IBS-QOL (FA and IF)
	56%/89% = 63%	0%/44% = 0%	-	FA: 31/25 = 125%
				IF: 9/10 = 84%
Craske SM	BSS	VSI	-	IBS-QOL (FA and IF)
	56%/82% = 68%	0%/23% = 0%	-	FA: 31/17 = 184%
				IF: 9/14 = 64%
Drossmann	Mc Gill pain Questionnaire	-	-	IBS-QOL
	2.77/4.58 = 60%	-	-	4.8/9.35 = 51%
Gaylord	IBS-Symptom Severity Score	VSI	Brief state inventory-depression	IBS-QOL
	(IBS-SSS)	Brief State Inventory-anxiety
	42.2/68.8 = 61%	1.16/5.78 = 20%	0.78/1.49 = 52%	3.7/0.19 = 36%
		1.64/3.86 = 42%
Moser	IBS-Impact Scale (IBS-IS)	HADS	-	SF-36
		Hospital Anxiety and Depression Scale
	40.9/60.8 = 67%	0.5/3.7 = 14%	-	24/117.9 = 20%
Payne and Blanchard	Composite Primary Symptom Reduction (CPSR)	STAI (state)	BDI	-
		STAI (trait)
	25%/75% = 33%	FALSE	0.4/6.3 = 6%	-
		FALSE
Shinozaki	Adequate Relief	State Trait Anxiety Inventory (state)	Self rating depression scale	SF-36
	Self Reported IBS Questionnaire (SIBSQ)	STAI (trait)	(SDS)
	30/81.8 = 37%	3.2/2.8 = 114%	0.1/1.8 = 6%	15.5/58.2 = 27%
	19.6/3.2 = 612%	4/1.5 = 267%

The percentages were calculated by dividing the treatment effect in the placebo group by the treatment effect in the intervention group and multiplying the quotient by 100. FA: Food avoidance; IF: Interference; VSI: Visceral sensitivity index.