Study	Reason for exclusion
Abbot 1995	The 'placebo intervention' was 'compressed air with freon' which, sprayed on skin, lowers temperature: impure placebo.
Abikoff 1985	All patients underwent a placebo run‐in period and only those not responding were included: not relevant participants.
Allen 1987	Dropout was > 50%.
Allen 1996	Randomisation was not described in the original paper. In a subsequent correspondence the authors described the method of randomisation: 'put three pieces of paper into a hat, each with the number 1, 2 or 3 and then drew a number each time a subject arrived and then assigned them accordingly '. There was no concealment of allocation. The number of patients in the placebo group was 105, in the no‐treatment group 75.
Amanzio 1999	Pain was induced experimentally.
Amanzio 2001	Not explicitly a randomised trial.
Archer 1992	Not a randomised study.
Arnett 1990	Inclusion of patients to no‐treatment groups started later than inclusion to active/placebo.
Avis 2008	Patients received payment.
Babizhayev 2001	No explicit randomisation between placebo and no‐treatment.
Barrett 1999	Low self‐esteem is not regarded a clinical problem.
Beck 2002	Male nursing home residents were not randomised, but 'assigned to the groups'. The proportion of males differed between the compared groups from 10% to 24%.
Benedetti 1998	Allocation to placebo and no‐treatment was not explicitly random.
Benedetti 1999b	Pain was induced experimentally.
Benedict 1989	The outcome in this study of chronic schizophrenia was reaction‐time which we regard not clinically relevant.
Bennet 2001	The outcome was not clinical.
Benton 1988	The trial studied the impact of vitamin supplements on the intelligence of normal schoolchildren, not regarded a clinical study.
Bergmann 1994	No untreated group.
Beutler 1988	The 'placebo' intervention consisted in 'paranormal healing at a distance', directed at a patient behind a screen, however the patients in the no treatment group also sat behind a screen, so the patient in both groups experienced the same: unacceptable no treatment group.
Bierman 1997	The outcome in this alcohol addiction trial was 'sleep quality': regarded not clinically relevant.
Björkstén 1986	Randomisation not mentioned.
Blackwell 1972	Participants were 'medical students': not a clinical study.
Blanchard 1978	6/30 patients were reallocated after randomisation.
Borden 1989	The clinically relevant outcomes (parents' and teachers' ratings) were not blinded.
Borkovec 1975	The participants were college students screened by group test program and receiving research credit for participation: not a clinical setting.
Bornstein 1973	The accumulated weight loss of the patients in the placebo group was 'positively reinforced': impure placebo.
Bouchet 1996	The participants were normal subjects.
Brown 1999	Pain was induced experimentally.
Buckalew 1972	The participants were normal subjects.
Bullock 1999	Drop out rate > 50%.
Bush 1985	Allocation of participants to the different groups of the trial was not concealed.
Butler 1984	The placebo intervention consisted in ordering difficult tasks for social phobics and practicing these tasks in ascending order: impure placebo.
Carlson 1993	The outcomes were 1) a questionnaire assessing the boys' attributions and 2) performance at an experimental word puzzle test: regarded not clinically relevant.
Carpenter 1994	Subjects were paid for participation.
Chambless 1984	Drop‐out rate > 50%.
Chen 1999	Unclear wether the trial was randomised. Authors contacted by e‐mail for clarification but did not respond.
Cole 1983	Randomisation not stated.
Corletto 1999	Placebo group got active treatment after 40 days.
Corson 1994	The placebo intervention implied pain inducing needle sticks: not a pure placebo intervention.
Cottraux 1986	Placebo group received not only a placebo intervention but also advice to reduce alcohol intake which is associated with smoking: impure placebo.
Cram 1980	The no treatment group sessions ('chart headaches only' ) also included discussions of 'situational themes': unacceptable no treatment group.
Cristofalo 1999	Normal subjects (athletes with no diagnosis of asthma).
Cullhed 1961	Allocation by day of admission.
Dahlquist 1986	Placebo group children were removed from parents. This was probably in itself anxiety inducing: impure placebo.
Daley 2007	According to the protocol patients received money for entering the trial.
Diamond 1995	The placebo used was saline. It is likely that saline has a physiological effect on congested nose, and is sold 'over the counter' in Denmark for this purpose: impure placebo.
Disney 1988	Not explicitly a randomised trial.
Dobia 1985	The 'placebo intervention' was relaxation therapy which was an integrated part of the experimental intervention: not a relevant placebo procedure.
Dundee 1988	Patients allocated by day of admittance.
Egbert 1964	The 'placebo' intervention in post‐operative patients having had intra‐abdominal surgery included instructions concerning pain modulating behaviour, e.g. how actively to relax abdominal muscles: impure placebo.
Eickholz 2002	Split mouth design. Teeth were randomised, not patients or treatment periods.
Elkin 1985	No untreated group.
Feather 1972	A non‐clinical experimental setting where pain was induced by heat.
Fevery 1990	The trial was designed to measure outcome after 6, 12 and 24 months. The placebo intervention was only comparable to the no treatment group the first 8 weeks: not a relevant comparison.
Fillmore 1992	A non‐clinical experimental setting with normal subjects.
Fillmore 1994	A non‐clinical experimental setting with normal subjects.
Fillmore 1994b	A non‐clinical experimental setting with normal subjects.
Flor 1983	Untreated group received co‐intervention not given to the placebo group.
Fuller 1986	No untreated group.
Gam 1998	The placebo group received massage and exercise, the no treatment group did not: differential co‐intervention.
Gelfand 1963	The subjects in this non‐clinical experimental pain trial were nursing students.
Goodale 1990	No clear indication in the trial report that 'the reading group' constituted a placebo group.
Gowdey 1967	'Normal subjects': not a clinical problem.
Gregorio 1996	The trial was designed to measure outcome after 6, 12 and 18 months. The placebo intervention was only comparable to the no treatment group the first 6 weeks: not a relevant comparison.
Gregory 1983	The study was 'designed to investigate whether elderly hospitalized people can improve their performance if they are permitted a second attempt at the Set Test, a verbal fluency task': not a therapeutical clinical study.
Gryll 1978	The allocation of participants was not explicitly stated to be random.
Haake 2007	No no‐treatment group. The group receiving acupuncture was not treated with conventional treatment given to the no‐acupuncture group.
Hale 1986	Allocation of participants was done in 'orderly sequence' following randomisation of the first patient.
Hall 1994	'Subjects reimbursed $20 at weeks 3 and 8 and $35 at week 12': participants paid.
Hargreaves 1983	This laboratory study was an uncontrolled trial.
Hayden 1996	The placebo used was saline. It is likely that saline has a physiological effect on congested nose, and is sold 'over the counter' in Denmark for this purpose: impure placebo.
Herth 2000	Placebo not explicitly mentioned.
Hogarty 1973	No untreated group.
Huber 1986	The clinician who decided to remove the placenta knew which patients were in the untreated group: not blindly assessed.
Jensen 1991	The trial was a 'laboratory study' with normal subjects: not a clinical study.
Kalman 1998	The placebo group received dietary advice which was withheld from the no‐treatment group.
Kanner 1999	The placebo treatment included 'intensive smoking‐cessation sessions' which was withheld from the the no‐treatment group.
Kelley 1976	Subjects were normal children: not a clinical study.
Khandwala 1997	According to personal communication with trial report authors, the vehicle was under suspicion of having an effect that was not only due to placebo and is actually sold 'over the counter' in the USA: impure placebo.
Klosko 1990	Patients in the untreated group continued on anxiolytic medication. Patients in the placebo group discontinued their medication. The groups in this anxiety trial are not comparable.
Korner 1982	No randomisation to placebo and untreated.
Lasagna 1954	The study was not randomised.
Levine 1980	The outcome was test anxiety which is not considered a clinically relevant outcome.
Liberman 1964	Not a randomised study.
Lopez 1999	Randomisation was conducted 'with due precaution to avoid differences among the subgroups in the children's mean ages and IQs'.
Lorr 1962	Drop‐out rate > 50%.
Lujan 1992	The headache was induced: an experimental setting.
Lynn 1983	The placebo procedure is described as being of 'an active nature': impure placebo.
Manner 1987	7/20 placebo treated patients receive sedative anticholinergic premedication (glycopyrrolate) compared to 0/18 untreated patients. Also unclear whether the untreated patients were part of the randomization: differential co‐intervention.
Marchand 1993	Patients were allocated through 'pseudo‐random assignment'. Contact to the authors clarified that this meant that randomisation was based on drawing pieces of paper with group assignments from a hat. There was no concealment of allocation.
McGrath 1988	Suggestions to reduce impact of possible triggers in 'untreated group': unacceptable no treatment group.
Meehan 1985	The no treatment group took prescribed and escape analgesics, the placebo group only escape analgesics.
Montgomery 1996	A non‐clinical experimental study with normal subjects.
Nikolaou 1998	Not a randomised trial.
Peart 1977	No randomisation to untreated and placebo.
Penman 1956	Post‐randomisation reallocations took place.
Pollo 2001	Allocation to placebo and no‐treatment was not explicitly random.
Price 1999	Healthy volunteers. Pain was induced experimentally.
Rampes 1997	Drop‐out rate 33/58=56% [> 50%].
Reich 1990	The participants were normal older subjects: not a clinical study.
Robertson 1991	'All subjects were paid'.
Rodriguez 1997	Post randomisation patient re‐allocation took place: 69 patients were randomised to the untreated group and but results were collected from 78 patients.
Roehrich 1993	This alcohol study had neuropsychological and psychological test variables as outcomes: regarded not clinically relevant.
Roelofs 2000	Paid healthy volunteers. Pain was induced experimentally.
Roos 1969	The placebo intervention was designed to include active components: not a pure placebo.
Roth 1986	Normal subjects.
Rustøen 1998	Placebo not explicitly mentioned.
Sarles 1977	Not a randomised trial.
Sartor 1980	Not properly randomised.
Shaw 1974	The placebo intervention consisted of listening to 'audiotapes designed to help persons cope with everyday fears and anxieties': not a pure placebo.
Sheikh 1986	The participants were older 'normal' volunteers with 'age associated memory impairment' : not a clinical study.
Silvestri 1977	Anxiety is the only outcome considered clinically relevant in this trial of the effect of implosive therapy for emotionally disturbed retardates, however, anxiety was not recorded in the no treatment group.
Skovlund 1991	No untreated group.
Smith 2002	The so‐called 'no treatment' group (but not the placebo group) received advice about changes in diet and the use of vitamin B6.
Spanos 1988	'All were paid $15 for their participation'.
Staats 1998	Pain induced by 'hand exposure to ice water': not a clinical study.
Stanley 1989	Not blindly assessed.
Suchman 1992	Not blindly assessed.
Tashkin 1977	Not a randomised trial.
Taylor 1977	Anti‐hypertensive drugs were given at variable dose as co‐intervention. More patients in the placebo group than in the untreated group were increased in dose: differential co‐intervention.
Vacc 1980	The investigation studied the effect of various interventions on maladaptive behaviour of otherwise normal children: not regarded a clinical study.
Van Damme 1998	Healthy volunteers.
Volweider 1981	Placebo procedure included physical exercise: not a pure placebo.
Weber 1975	Averaged Electroencephalic audiometry (AEA) thresholds was the outcome in this study of CNS stimulant medication on children with minimal brain damage: outcome regarded not clinically relevant.
Weintraub 1992	The placebo period (week 160 to 190) was followed by the untreated period (week 190 to 210), (no randomisation).
Windle 2001	Allocation of patients by alternation.
Winnan 1982	The Bernstein test is a diagnostic test. Pain was induced by infusion of acid: not a therapeutic clinical study.
Worner 1992	Drop out rate > 50%.
Zeisset 1968	The outcome was 'interview anxiety' which was not considered clinically relevant as a measure for general anxiety.

Impure placebos: interventions with clearly specified contents or procedures that have an effect which, with considerable likelihood, goes beyond the effect of the treatment ritual. Such interventions are mostly 1) physical or pharmacological vehicles (see, e.g., Khandwala 1997), or 2) psychological 'placebos' with clear behavioural‐cognitive therapeutical elements (see, e.g., Bornstein 1973) or direct health related advice (see, e.g., Cottraux 1986).