Mark van der Gaag

Prof. Dr. Mark van der Gaag

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Research Focus & Metrics

Academic Career Length

37Years (1990-Present)

(Calculated once Scilit publication data is synced: current year − year of first publication + 1)

Representative Publications

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1 July 2006 in Schizophrenia Research
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Journal Article
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MGMark van der Gaag
Mark van der Gaag
THTonko Hoffman
Tonko Hoffman
MRMila Remijsen
Mila Remijsen
RHRon Hijman
Ron Hijman
LHLieuwe De Haan
Lieuwe De Haan
DWDurk Wiersma
Durk Wiersma

19 April 2012 in Schizophrenia Bulletin
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Journal Article
Open access
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HIHelga K. Ising
Helga K. Ising
WVWim Veling
Wim Veling
RLRachel L. Loewy
Rachel L. Loewy
MRMarleen W. Rietveld
Marleen W. Rietveld
JRJudith Rietdijk
Judith Rietdijk
MGMark van der Gaag
Mark van der Gaag
In order to bring about implementation of routine screening for psychosis risk, a brief version of the Prodromal Questionnaire (PQ; Loewy et al., 2005) was developed and tested in a general help-seeking population. We assessed a consecutive patient sample of 3533 young adults who were help-seeking for nonpsychotic disorders at the secondary mental health services in the Hague with the PQ. We performed logistic regression analyses and CHi-squared Automatic Interaction Detector decision tree analysis to shorten the original 92 items. Receiver operating characteristic curves were used to examine the psychometric properties of the PQ-16. In the general help-seeking population, a cutoff score of 6 or more positively answered items on the 16-item version of the PQ produced correct classification of Comprehensive Assessment of At-Risk Mental State (Yung et al., 2005) psychosis risk/clinical psychosis in 44% of the cases, distinguishing Comprehensive Assessment of At-Risk Mental States (CAARMS) diagnosis from no CAARMS diagnosis with high sensitivity (87%) and specificity (87%). These results were comparable to the PQ-92. The PQ-16 is a good self-report screen for use in secondary mental health care services to select subjects for interviewing for psychosis risk. The low number of items makes it quite appropriate for screening large help-seeking populations, thus enhancing the feasibility of detection and treatment of ultra high-risk patients in routine mental health services.

1 March 2015 in European Psychiatry
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Journal Article
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SSS.J. Schmidt
S.J. Schmidt
FSF. Schultze-Lutter
F. Schultze-Lutter
BSB.G. Schimmelmann
B.G. Schimmelmann
NMN.P. Maric
N.P. Maric
RSR.K.R. Salokangas
R.K.R. Salokangas
SRS. Ruhrmann
S. Ruhrmann
This guidance paper from the European Psychiatric Association (EPA) aims to provide evidence-based recommendations on early intervention in clinical high risk (CHR) states of psychosis, assessed according to the EPA guidance on early detection. The recommendations were derived from a meta-analysis of current empirical evidence on the efficacy of psychological and pharmacological interventions in CHR samples. Eligible studies had to investigate conversion rate and/or functioning as a treatment outcome in CHR patients defined by the ultra-high risk and/or basic symptom criteria. Besides analyses on treatment effects on conversion rate and functional outcome, age and type of intervention were examined as potential moderators. Based on data from 15 studies (n = 1394), early intervention generally produced significantly reduced conversion rates at 6- to 48-month follow-up compared to control conditions. However, early intervention failed to achieve significantly greater functional improvements because both early intervention and control conditions produced similar positive effects. With regard to the type of intervention, both psychological and pharmacological interventions produced significant effects on conversion rates, but not on functional outcome relative to the control conditions. Early intervention in youth samples was generally less effective than in predominantly adult samples. Seven evidence-based recommendations for early intervention in CHR samples could have been formulated, although more studies are needed to investigate the specificity of treatment effects and potential age effects in order to tailor interventions to the individual treatment needs and risk status.

1 March 2015 in European Psychiatry
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Journal Article
Closed access
FSF. Schultze-Lutter
F. Schultze-Lutter
CMC. Michel
C. Michel
SSS.J. Schmidt
S.J. Schmidt
BSB.G. Schimmelmann
B.G. Schimmelmann
NMN.P. Maric
N.P. Maric
JKJ. Klosterkötter
J. Klosterkötter
The aim of this guidance paper of the European Psychiatric Association is to provide evidence-based recommendations on the early detection of a clinical high risk (CHR) for psychosis in patients with mental problems. To this aim, we conducted a meta-analysis of studies reporting on conversion rates to psychosis in non-overlapping samples meeting any at least any one of the main CHR criteria: ultra-high risk (UHR) and/or basic symptoms criteria. Further, effects of potential moderators (different UHR criteria definitions, single UHR criteria and age) on conversion rates were examined. Conversion rates in the identified 42 samples with altogether more than 4000 CHR patients who had mainly been identified by UHR criteria and/or the basic symptom criterion ‘cognitive disturbances’ (COGDIS) showed considerable heterogeneity. While UHR criteria and COGDIS were related to similar conversion rates until 2-year follow-up, conversion rates of COGDIS were significantly higher thereafter. Differences in onset and frequency requirements of symptomatic UHR criteria or in their different consideration of functional decline, substance use and co-morbidity did not seem to impact on conversion rates. The ‘genetic risk and functional decline’ UHR criterion was rarely met and only showed an insignificant pooled sample effect. However, age significantly affected UHR conversion rates with lower rates in children and adolescents. Although more research into potential sources of heterogeneity in conversion rates is needed to facilitate improvement of CHR criteria, six evidence-based recommendations for an early detection of psychosis were developed as a basis for the EPA guidance on early intervention in CHR states.

1 September 2013 in Schizophrenia Research
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Journal Article
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MGMark van der Gaag
Mark van der Gaag
FSFilip Smit
Filip Smit
ABAndreas Bechdolf
Andreas Bechdolf
PFPaul French
Paul French
DLDon H. Linszen
Don H. Linszen
PCPim Cuijpers
Pim Cuijpers

1 March 2015 in JAMA Psychiatry
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Journal Article
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DBDavid P. G. van Den Berg
David P. G. van Den Berg
PBPaul A. J. M. de Bont
Paul A. J. M. de Bont
BVBerber M. van der Vleugel
Berber M. van der Vleugel
CRCarlijn de Roos
Carlijn de Roos
AJAd de Jongh
Ad de Jongh
MGMark van der Gaag
Mark van der Gaag
Research from JAMA Psychiatry — Prolonged Exposure vs Eye Movement Desensitization and Reprocessing vs Waiting List for Posttraumatic Stress Disorder in Patients With a Psychotic Disorder — A Randomized Clinical Trial