Does depression explain poor effort on Symptom Validity Tests (SVT)?

Background and aims

Valid assessments require sufficient effort from the part of the testee. Motivation may be compromised, particularly in psychiatric conditions. We examined associations between response bias on free recall and self-reported symptoms in depressed and PTSD patients.

Participants and methods

This is a cross-sectional study. Patients had depression (n = 48), or PTSD or other anxiety disorders (n = 37). A control group (n = 47%) had chronic pain disorder, fibromyalgia or chronic fatigue. The Green Word Memory Test (GWMT) was administered to all subjects. The Structured Inventory of Malingered. Symptomatology (SIMS), and the Beck Depression Inventory (BDI-II) were administered in subsamples. Study outcome was self-reported depressive symptoms in Symptom Validity Test (SVT) negative cases.

Results

Average age of the participants was 45.1 years (SD 9.5), 48.5% were female. GWMT was positive in 52.3% of all cases, GWMT and SIMS were positive in 33.8%, and GWMT and SIMS were negative in 37.7%. No significant group effects on GWMT were found. Average BDI-II scores were 32.8 (SD 13.9) for depressed patients, 28.3 (15.5) for those with anxiety disorders, and 27.6 (14.1) for controls (P = 0.43). Seventy-eight percent of depressed GWMT negative cases reported at least moderate depressive symptoms (BDI-II > 18), and 44.4% severe symptoms (BDI-II > 29). Approximately half of the GWMT negative cases with anxiety disorders and controls scored BDI-II > 18.

Conclusions

Non credible test performance is prevalent in disability claimants with affective, mood disorders. However, depressive symptoms per se do not explain poor effort on cognitive tasks.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Symptom Validity Testing (SVT) and Social Security Disability Claims

Background and aims

Over 50% of adult disability claimants fail some form of SVT. While some over report psychological, affective symptoms, others may report incredible cognitive symptoms. We examined effects of different types of response bias on free recall and self-reported depression.

Participants and methods This is a single site cross-sectional study using a convenience sample (n = 224) of disability claimants in the Netherlands. The Green Word Memory Test (GWMT) was administered to all subjects. The Amsterdam Short Term Memory Test (AKTG), the Structured Inventory of Malingered. Symptomatology (SIMS), and the beck depression inventory (BDI-II) were administered in subsamples. Participant classification according to GWMT and SIMS outcomes resulted in four groups, G+/S+, G+/S−, G−/S+ and G−/S−.

Results

Average age of the participants was 46.3 years (SD 9.9), 41.5% were female, and 43% were higher educated. GWMT was positive in 48.2% of all subjects, and 27.6% scored positive on both GWMT and SIMS. Analysis of variance of GWMT Free recall and Beck depression scores showed significant group differences [F(3, 123) = 33.21, P = .000] and [F(3, 106) = 25.17, P = .000] respectively.

Conclusions

Non credible test performance was prevalent in this Dutch study of disability claimants. Insufficient effort and over reporting of psychological symptoms are associated with different score profiles on regular tests and self-rating scales.

Disclosure of interest

The author receives funding for his work as a neuropsychologist in an expertise setting.

Occurrence and potential health risk of Cryptosporidium and Giardia in different water catchments in Belgium

Human wastewater and livestock can contribute to contamination of surface water with Cryptosporidium and Giardia. In countries where a substantial proportion of drinking water is produced from surface water, e.g., Belgium, this poses a constant threat on drinking water safety. Our objective was to monitor the presence of Cryptosporidium and Giardia in different water catchment sites in Belgium and to discriminate between (oo)cysts from human or animal origin using genotyping. Monthly samples were collected from raw water and purified drinking water at four catchment sites. Cryptosporidium and Giardia were detected using USEPA method 1623 and positive samples were genotyped. No contamination was found in purified water at any site. In three catchments, only low numbers of (oo)cysts were recovered from raw water samples (<1/liter), but raw water samples from one catchment site were frequently contaminated with Giardia (92 %) and Cryptosporidium (96 %), especially in winter and spring. Genotyping of Giardia in 38 water samples identified the presence of Giardia duodenalis assemblage AI, AII, BIV, BIV-like, and E. Cryptosporidium andersoni, Cryptosporidium suis, Cryptosporidium horse genotype, Cryptosporidium parvum, and Cryptosporidium hominis were detected. The genotyping results suggest that agriculture may be a more important source of surface water contamination than human waste in this catchment. In catchment sites with contaminated surface water, such as the Blankaart, continuous monitoring of treated water for the presence of Cryptosporidium and Giardia would be justified and (point) sources of surface water contamination should be identified.