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Design choices when estimating the treated incidence of schizophrenia

Published online by Cambridge University Press:  26 July 2019

Simon J. Hogerzeil
Affiliation:
Parnassia Psychiatric Institute, The Hague, The Netherlands; Leiden University Medical Center, Leiden, The Netherlands
Albert M. van Hemert
Affiliation:
Parnassia Psychiatric Institute, The Hague, The Netherlands; Leiden University Medical Center, Leiden, The Netherlands
Corresponding
E-mail address:
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Abstract

Type
Correspondence
Copyright
Copyright © Cambridge University Press 2019 

Anderson et al. (Reference Anderson, Norman, MacDougall, Edwards, Palaniyappan, Lau and Kurdyak2018) estimate the gap between the number of incident cases of schizophrenia aged 16–50 in Ontario, Canada in 1997–2015, and the number who were enrolled into Early Psychosis Intervention (EPI) services. Their analysis is a direct comparison between administrative records and the standard method for estimating the treated incidence.

The standard method (known as the ‘first-contact design’) involves screening subjects for signs of psychosis when they present for psychiatric treatment. Subjects screened positive then undergo standardized diagnostic procedures to establish the criteria for schizophrenia. But studies based on administrative records have suggested that two out of three cases may be missed this way (Hogerzeil et al., Reference Hogerzeil, van Hemert, Rosendaal, Susser and Hoek2014; Pedersen et al., Reference Pedersen, Mors, Bertelsen, Waltoft, Agerbo, McGrath, Mortensen and Eaton2014; Jongsma et al., Reference Jongsma, Turner, Kirkbride and Jones2019).

Anderson et al. (Reference Anderson, Norman, MacDougall, Edwards, Palaniyappan, Lau and Kurdyak2018) also found that two out of three cases of schizophrenia had remained unknown to EPI services. Not all cases met EPI-services' inclusion criteria, but still a substantial number of true cases of schizophrenia had been missed. In their discussion, Anderson et al. (Reference Anderson, Norman, MacDougall, Edwards, Palaniyappan, Lau and Kurdyak2018) focused on the issue of incomplete coverage of services, but this is only one of several design aspects that matter.

We propose to distinguish three design aspects where complete case finding can go wrong: coverage of services, time frame of the diagnosis, and accuracy of the diagnosis. We believe that these distinctions can help to understand the five- to ten-fold variation in incidence between populations, which is commonly reported but only partially explained (Mcgrath et al., Reference Mcgrath, Saha, Welham, El Saadi, MacCauley and Chant2004; Jongsma et al., Reference Jongsma, Gayer-Anderson, Lasalvia, Quattrone, Mule, Szoke, Selten, Turner, Arango, Tarricone, Berardi, Tortelli, Llorca, de Haan, Bobes, Bernardo, Sanjuán, Santos, Arrojo, Del-Ben, Menezes, Velthorst, Murray, Rutten, Jones, van Os, Morgan and Kirkbride2018, Reference Jongsma, Turner, Kirkbride and Jones2019).

(x) Coverage of services where cases can be detected. These may range from (1) very specialized services such as EPI services, emergency or inpatient services, extending to (2) general psychiatric or addiction services, and further to (3) primary care or somatic medical care or ultimately to (4) the general population.

(y) Time frame of the diagnosis, the interval allowed between the first contact with a service and the moment a diagnosis can be made. It may range from (1) case ascertainment at first-contact only, extending to (2) later stages of treatment, e.g. subjects presenting initially with another diagnosis, ultimately extending to a (3) life-time follow-up.

(z) Accuracy of the diagnosis, ranging from diagnosis based on (1) research diagnostic procedures, extending to (2) clinical criteria diagnoses (e.g. DSM-5 or ICD-10) and (3) non-standardized diagnostic procedures.

This can be illustrated in 3D, where design choices along the {x y z} axes determine a box, the volume of which represents the incidence estimate. Figure 1 illustrates how the first contact design (solid box; i.e. typically measured as first contacts at specialized services, using research diagnoses) results in a lower incidence compared to cumulative records (dotted box; i.e. typically measured at all psychiatric services, using clinical diagnoses over much longer timespans).

Fig. 1. Graphical illustration of three design aspects for studies measuring the incidence of schizophrenia. The volume of the solid box represents the incidence as estimated in a typical first-contact design and that of the dotted box the incidence as estimated in electronic administrative records.

Case-register studies from the 1950s to the 1970s typically focused on inpatient hospital services, with long time frames and non-standardized diagnoses. The first-contact studies of the 1990s and later focused on a wider coverage of services and better diagnostic accuracy, while restricting the timeframe (Jablensky et al., Reference Jablensky, Sartorius, Ernberg, Anker, Korten, Cooper, Day and Bertelsen1992). That approach has high specificity but low sensitivity: many subjects with an ultimate diagnosis of schizophrenia will be missed because they do not meet criteria for the disorder when they first seek treatment (Rietdijk et al., Reference Rietdijk, Hogerzeil, van Hemert, Cuijpers, Linszen and van der Gaag2011; Hogerzeil et al., Reference Hogerzeil, van Hemert, Rosendaal, Susser and Hoek2014).

Longer time frames became possible with (a) the wide adoption DSM or ICD based clinical diagnoses and (b) well maintained administrative records in (c) institutions serving all psychiatric needs of well-defined populations. Such databases can now be used to reconstruct diagnostic histories or treatment pathways through services, up to the first diagnosis of schizophrenia, capturing new onsets along pathways that cannot be covered with the standard approach. This new approach is more sensitive, although it might come at the expense of some diagnostic specificity.

The study by Anderson et al. (Reference Anderson, Norman, MacDougall, Edwards, Palaniyappan, Lau and Kurdyak2018) is the second to compare first-contact and cumulative methods directly. Their study can be understood as a replication of our finding (Hogerzeil et al., Reference Hogerzeil, van Hemert, Rosendaal, Susser and Hoek2014) that in administrative data the incidence of treated schizophrenia is two- to three-fold higher than detected using the first-contact design. Now replicated, this finding has obvious implications for estimates of the number of cases affected and for the organization of services. Furthermore, considering subjects with psychosis at first contact as ‘prototype cases’ may have distorted our understanding of schizophrenia by spuriously highlighting a younger age of onset and a more acute clinical presentation than seen in actual administrative records (Hogerzeil et al., Reference Hogerzeil, van Hemert, Veling and Hoek2016).

Study design matters a lot when estimating the incidence of schizophrenia. To interpret incidence studies or to make meaningful comparisons between them, we need a more elaborate classification of study designs, as suggested here.

Author ORCIDs

Simon J. Hogerzeil, 0000-0001-6269-179X

Albert M. van Hemert, 0000-0003-3421-355X

References

Anderson, K, Norman, R, MacDougall, AG, Edwards, J, Palaniyappan, L, Lau, C and Kurdyak, P (2018) Estimating the incidence of first-episode psychosis using population-based health administrative data to inform early psychosis intervention services. Psychological Medicine, 19 doi:10.1017/S0033291718002933 (Epub ahead of print).Google ScholarPubMed
Hogerzeil, SJ, van Hemert, AM, Rosendaal, FR, Susser, E and Hoek, HW (2014) Direct comparison of first-contact versus longitudinal register based case finding in the same population: early evidence that the incidence of schizophrenia may be three times higher than commonly reported. Psychological Medicine 44, 34813490.CrossRefGoogle ScholarPubMed
Hogerzeil, SJ, van Hemert, AM, Veling, W and Hoek, HW (2016) Incidence of schizophrenia among migrants in the Netherlands: a direct comparison of first contact longitudinal register approaches. Social Psychiatry and Psychiatric Epidemiology 52, 147154.CrossRefGoogle ScholarPubMed
Jablensky, AV, Sartorius, N, Ernberg, G, Anker, M, Korten, A, Cooper, JE, Day, R and Bertelsen, A (1992) Schizophrenia: manifestations, incidence and course in different cultures. A World Health Organization ten-country study. Psychological Medicine. Monograph Supplement 20, 197.10.1017/S0264180100000904CrossRefGoogle ScholarPubMed
Jongsma, HE, Gayer-Anderson, C, Lasalvia, A, Quattrone, D, Mule, A, Szoke, A, Selten, J-P, Turner, C, Arango, C, Tarricone, I, Berardi, D, Tortelli, A, Llorca, P-M, de Haan, L, Bobes, J, Bernardo, M, Sanjuán, J, Santos, JL, Arrojo, M, Del-Ben, CM, Menezes, PR, Velthorst, E, Murray, RM, Rutten, BP, Jones, PB, van Os, J, Morgan, C, Kirkbride, JB and European Network of National Schizophrenia Networks Studying Gene-Environment Interactions Work Package 2 (EU-GEI WP2) Group (2018) Treated incidence of psychotic disorders in the multinational EU-GEI Study. JAMA Psychiatry 75, 3646CrossRefGoogle ScholarPubMed
Jongsma, HE, Turner, C, Kirkbride, JB and Jones, PB (2019) International incidence of psychotic disorders, 2002–17: a systematic review and meta-analysis. The Lancet Public Health 4, e229e244.CrossRefGoogle ScholarPubMed
Mcgrath, J, Saha, S, Welham, J, El Saadi, O, MacCauley, C and Chant, D (2004) A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology. BMC Medicine 2, 291.10.1186/1741-7015-2-13CrossRefGoogle ScholarPubMed
Pedersen, CB, Mors, O, Bertelsen, A, Waltoft, BL, Agerbo, E, McGrath, JJ, Mortensen, PB and Eaton, WW (2014) A comprehensive nationwide study of the incidence rate and lifetime risk for treated mental disorders. JAMA Psychiatry 71, 573581.CrossRefGoogle Scholar
Rietdijk, J, Hogerzeil, SJ, van Hemert, AM, Cuijpers, P, Linszen, DH and van der Gaag, M (2011) ‘Pathways to psychosis: help-seeking behavior in the prodromal phase. Schizophrenia Research 132, 213219.CrossRefGoogle ScholarPubMed
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