Modelo de datos

Figure 1 provides full details of the screening and exclusion process. The search yielded 22 studies, which provided 25 prevalence rates across 16 cohorts consisting of 112,617 separate participants. Table 2 summarises the key details regarding the studies, including the samples and rates, to provide context to the following results. The identified studies used a variety of different measures. Thirteen were interview studies, seven self-report questionnaires, and two administered an interview schedule in a self-report questionnaire format. These measures utilised different response options, from dichotomous yes-no to likert scales. Unless already determined, the overall observed rate was calculated by any positive endorsement.

Further details of the measures used, the items required for presence of hearing voices, and the endorsement thresholds are provided in Table 3.

24

Records identified through database searching (N=3594) (PSYCHINFO: 827; MEDLINE: 561; EMBASE: 1199;

WEB OF SCIENCE: 1007)

25 Table 2

Cohorts and data sources for identified studies

Cohort (duration) Location Data source

Recruitment

strategy N

Age

range Measure instrument Type

Observed rate

McGrath et al. (2015) Multistage, clustered-area

26

Netherlands: throughout Van Nierop et al.

(2011)

Sweden: Uppsala region Therman, Suvisaari,

& Hultman (2014)

Norway: throughout Krakvik et al. (2015) Random national statistic selection

2533 18+ LSHS-modified: Norwegian version

QST 7.25% ^w (6.16, 8.35)

27

Mater University of Queensland Study of

Pregnancy (MUSP) (2002-04)

Australia: Queensland Scott et al. (2008) ^e Restricted opportunistic sampling

2441 18-23 CIDI 2.1 psychosis screen INT 3.44% (-)

Dutch general population (2006-08)

Netherlands: throughout Sommer et al. (2010)

e

Non-random, biased

4135 18+ LSHS-modified: Dutch version

QST 11.54% (-)

Community residents (-) Korea: no specification Chang et al. (2015) ^e (-) 223 18-65 LSHS-Revised: Korean version

UK: South London Freeman & Fowler ^e (2009)

17000 20-70 Standard interview schedule (created by authors)

UK: throughout West (1948) ^e Biased random, convenience

1519 (-) Standard interview schedule (as above)

QST/

INT

8.82% (-)

Key: CIDI = Composite International Diagnostic Interview; SPIKE = Structured Psycho-pathological Interview and Rating of the Social Consequences of Psychological Disturbances for Epidemiology; CAPE = Community Assessment of Psychic Experiences; CBQ = Cardiff Beliefs Questionnaire; LSHS = Launay–Slade Hallucination Scale;

RHS = Revised Hallucination Scale; CAPS = Cardiff Anomalous Perceptions Scale; INT = Interview, QST = Questionnaire

Notes: (-) = not stated in paper, c = CI were calculated from standard error rates, e = excluded due to poor quality, n = not included in quantitative synthesis due to overlapping sample, w = rate was weighted by authors

28 Table 3

Measures used across studies

Measure No. Type Description Item Response options

World Health

12 INT The CIDI is a diagnostic tool for epidemiological studies, which expands the Diagnostic Interview Schedule (DIS) to include both ICD and DSM classification, for cross-national comparisons (Cooper, Peters, & Andrews, 1998).

CIDI 2.1: It contains a psychosis screen including 17 delusion items and 2 hallucination items.

CIDI 3: Due to poor reliability and validity of earlier CIDI versions, a new psychosis add-on instrument was constructed. This includes a carefully worded introduction using normalising language to help improve the accuracy of responses (Kessler, Wittchen, Abelson, & Zhao, 2000). It contains six structured questions about the DSM-IV (APA, 1994) delusions and hallucinations found to more strongly predict clinician-diagnosed non-affective psychosis in the NCS (Kendler, Gallagher, Abelson, & Kessler, 1996; Kessler et al., 2005). These questions were modified with a clinical expert to align with how symptoms are experienced by community cases and therefore capture subclinical psychosis rather than full psychotic disorder.

CIDI 2.1: G18 Have you more than once heard things that other people couldn’t hear, such as a voice? G19 Did you ever hear voices others could not hear? Yes / No CIDI 3: The next questions are about unusual things, like seeing visions or hearing voices. We believe that these things may be quite common, but we don't know for sure because previous research has not done a good job asking about them. So please take your time and think carefully before answering. […] The second thing is hearing voices that other people could not hear. I don't mean having good hearing, but rather hearing things that other people said did not exist, like strange voices coming from inside your head talking to you or about you, or voices coming out of the air when there was no one around. Did you ever hear voices in this way? Did this ever happen when you were not

dreaming, not half-asleep, and not under the influence of alcohol or drugs?^* Yes / No

1 INT The SPIKE was developed for psychiatric epidemiological surveys (Angst, Dobler-Mikola, & Binder, 1984). In 2008 a new psychotic symptoms section was added to assess the sub-threshold range of these experiences in the general population. It includes four screening questions representing four syndromes.

"To hear voices that others don’t" If positively endorsed item is followed by a series of detailed and more specific questions about the pertinent symptoms. Yes / No

29

Standard interview schedule:

2 INT This standard interview scheduled was developed by Sidgwick and colleagues (1894) for the purpose of their census of hallucinations. It begins with an explanation that the question relates to experiences that Psychologists would describe as “casual hallucinations of sane persons”.

Have you ever, when believing yourself to be completely awake, had a vivid impression of seeing or being touched by a living being or inanimate object, or of hearing a voice;

which impression, so far as you could discover, was not due to any external physical cause? Anyone answering yes are given schedule B with follow up questions differentiating the experience. Yes / No

4 QST The original LSHS (Launay & Slade, 1981) consisted of 12 true/false items assessing hallucinatory predisposition. Bentall and Slade’s (1985) LSHS-R added a five-point Likert certainty scale. Morrison and colleagues (2000) added visual hallucination items, resulting in the 16 item RHS endorsed by frequency. Laroi and Van der Linden (2005) incorporated further hallucinatory modalities and modified the items found to pose research problems, resulting in 17 items with the original certainty scale.

In the past I have had the experience of hearing a person’s voice and then found that there was no-one there? ^**

LSHS-R/modified: Certainly does not/ Possibly does not / Unsure / Possibly / Certainly does apply to me

RHS: Never / Sometimes / Often / Almost always Community Assessment of

Psychic Experiences (CAPE):

1 QST The CAPE (Stefanis et al., 2002), is a modified version of the Peters et al. Delusions Inventory (Peters, Joseph, & Garety, 1999). It contains 42 positive, negative, and depressive items explicitly designed to probe clinically relevant PEs.

Do you ever hear voices when you are alone?

Never / Sometimes / Often / Almost always Cardiff Beliefs

Questionnaire (CBQ):

1 QST The CBQ (Pechey & Halligan, 2011) contains 48-items (27 delusion-like/paranormal/religious beliefs; 13 societal/cultural beliefs; and eight anomalous experiences (four paranormal, two hallucinations, and two delusions)).

How often have you heard voices when no one is around?

Never / Rarely / Sometimes / Often Cardiff Anomalous

Perceptions Scale (CAPS)

1 QST The CAPS (Bell, Halligan, & Ellis, 2006) is a 32-item questionnaire, developed in both non-clinical and psychotic groups, to assess perceptual anomalies.

Do you ever hear voices saying words or sentences when there is no one around that might account for it?^*** Yes/No Notes: INT = Interview, QST = Questionnaire; *McGrath et al. (2015) included some surveys using versions of CIDI (numbers not provided) containing an item phrased: “Did you ever hear things that other people said did not exist, like strange voices coming from inside your head talking to you or about you, or voices coming out of the air when there was no one around.” However, contact with the lead author confirmed that the final survey rates related to verbal hallucinations only. ** Additional items: Krakvik et al.

(2015) “I often hear a voice speaking my thoughts aloud”; Sommer et al. (2010) “I have been troubled by hearing voices in my head” ***Additional items: Freeman & Fowler (2009) “Do you ever hear voices commenting on what you are thinking or doing?”, “Have you ever heard two or more unexplained voices talking with each other?”

30 1.4.2 Study quality

Table 4 summarises the study quality scores. An independent rater (a Trainee Clinical Psychologist, UCL) scored 11 randomly selected papers (indicated in bold) using the same tool and guidelines. The independent ratings were compared and discussed. Any differences in ratings were resolved by discussion.

Table 4

Risk of bias assessment scores

Note: Scoring: Y= met criteria, N=did not meet criteria, U=unclear; ^a Short hand summary: 1, sample frame; 2, sampling/recruitment, 3, sample size; 4, sample characteristics described; 5, coverage bias; 6, measurement validity; 7, measurement reliability; 8, appropriate statistical reporting; ^b Excluded on the basis of poor methodology; ^c Not included in the quantitative synthesis due to overlapping WHO-MHS samples

Quality rating criteria ^a

31 On the basis of their quality ratings, seven studies were excluded. The independent rater agreed with all exclusions of studies. Three questionnaire studies were excluded as they did not meet the minimum sample size set out in the critical appraisal tool (N>240). These studies were also rated ‘poorly’ overall. The lack of detail provided in two of these studies (Chang et al., 2015; Langer et al., 2015) which had sample sizes of 223 and 68 respectively, made it difficult to rate the quality of the methodology and therefore to determine the validity of the prevalence estimate. The third study recruited via leaflet distribution to postcodes scoring highly on indexes of deprivation in South London with a poor response rate (Freeman & Fowler, 2009).

This led authors to conclude that the sample of 200 was unlikely to be truly representative of the UK general population. Given the priority placed on estimates reflecting wider general population prevalence within this review, this also lowered its quality rating.

A further two studies, conducted by the Society of Psychical Research, were determined to have poor methodology throughout (Sidgwick et al., 1894; West et al., 1948). The only quality rating that could be confidently asserted was sufficient sample size. In terms of their methodology, their sample frames were unclear and as has been noted by previous reviewers, their recruitment methods were biased and unsystematic (Beavan et al., 2011). In particular, they used primarily friends and society acquaintances (Sidgwick et al., 1894) or a motivationally biased sample of voluntary helpers (West et al., 1948) and their respective personal networks to collect data using their study specific census asked in questionnaire format. The limited monitoring and control over this process led to poor ratings regarding reliability. The latter study also acknowledged numerous misunderstandings and indeterminable cases within their rate.

32 In another excluded study (Sommer et al., 2010) the overall aim was to recruit voice-hearers for a comparison study. The questionnaire was administered through a website containing information on voice hearing and the lead author confirmed that the design of this recruitment webpage “was not intended to give an exact reflection of the general population” (Email correspondence, I. Sommer, 21.03.17). As such their sample frame and recruitment was biased towards voice hearers. The final excluded study used the MUSP’s CIDI 2.1 results, however the exact item phrasing could not be established and consequently it was unclear whether endorsement related to voices or broader

‘things’ (Scott et al., 2008). Recruitment from the original MUSP study involved identifying women across the antenatal catchment area covered by a single study hospital. Their offspring were then followed up after 21 years, which formed the sample frame for the current study. Due to the nature of the follow up, this meant that the sample was restricted to 21-23 year olds. Recruitment methods that were used to follow up these individuals were also limited by financial constraints and participant availability, further reducing the representativeness of the sample. For these studies, the only quality items that could be confidently asserted were sufficient sample size and consistent web-based questionnaire administration or sufficient MUSP sample description. As such, their overall low quality rating and bias within their methodology led to their exclusion.

The quality ratings were used to structure, critically analyse, and weight the following results. First a quantitative synthesis of the identified prevalence rates is presented. Following this, the studies, their quality and contribution to the overall rate will be described, starting by evaluation of the sampling populations and recruitment methodologies and finishing with appraisal of the methods for measuring the condition.

33 1.4.3 Prevalence rate

Ten rates from nine studies using separate samples were included in the quantitative synthesis, including seven interview rates and three questionnaire rates.

The median prevalence was 2.6% (range=1.88%-15.3%; IQR=2.25%-5.51%). The mean prevalence was 4.54% (SD=4.13%). Prevalence percentiles and quartiles of this estimate are present in Table 5, alongside existing PE estimates. The difference between the median and mean values indicated that the distribution of rates was skewed (Sara et al., 2008). The distribution was found to significantly differ from normality (D(10)=0.272, p=0.034) with a positive skew (z=3.43), particularly influenced by one questionnaire study (z=2.61) (Pechey & Halligan, 2012). The 10%

to 90% range shows that the central portion of the distribution varies over a six- to seven- fold range. The variation in rates is represented in Figure 2.

Table 5

Notes: ^a Rates obtained from present review; ^b Rates obtained by Beavan et al (2011);

c Rates obtained from Linscott & van Os (2013)

34 Figure 2

Cumulative frequency of voice-hearing