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PubMedDate not supplied

Accuracy of intraoperative frozen section diagnosis in head and neck surgery: experience at a university medical center.

We performed 2,210 intraoperative frozen sections on 258 patients from the Otolaryngology-Head and Neck Surgery Service in 1990 and 1991. Surgery involved a wide variety of benign and malignant lesions. Techniques included biopsies for diagnosis, simple excision, thyroid and salivary gland surgeries, lymph node biopsies, composite resections with radical neck dissections, laryngectomies, and skull base surgeries. During the 2-year period, 1,947 (88.1%) sections were requested for evaluation of surgical margins, 258 (11.7%) for diagnosis, and five (0.2%) cases for tissue identification. There was disagreement between the frozen section and permanent section in 46 (2.1%) cases, and the deferral diagnosis rate was 0.8%. Disagreements were the result of sampling errors in 33 and interpretive errors in 13 cases. There were six (0.3%) false-negative diagnosis of malignancy and four (0.2%) false-positive diagnoses of malignancy. Three of these had an impact on patient care as discussed. We recommend careful sampling and sectioning of small biopsies and the need for vigilant communication between surgeon and pathologist.

Cytodiagnosis↗

PubMed2004

Estimating pairwise relatedness from dominant genetic markers.

Knowledge of the genetic relatedness between a pair of individuals is important in many research areas of quantitative genetics, conservation genetics, evolution and ecology. Many estimators have been developed to estimate such pairwise relatedness (r) using codominant markers, such as microsatellites and enzymes. In contrast, only two estimators are proposed to use dominant markers, such as random amplified polymorphic DNAs (RAPDs) and amplified fragment length polymorphisms (AFLPs), in relatedness inference. They are both biased estimators, and their statistical properties and robustness to the sampling errors in allele frequency have not been investigated. In this short paper, I propose two new pairwise relatedness estimators for dominant markers, and compare them in precision, accuracy and robustness to sampling with the two previous estimators using simulations. It was found that the new estimator based on the least squares approach is unbiased when allele frequencies are known or estimated from a sample without correcting for sampling effects. It has, however, a low precision and as a result, an intermediate overall performance among the four estimators in terms of the mean squared deviation (MSD) of estimates from actual values of r. The new estimator based on a similarity index is slightly biased but has generally the lowest MSD among the four estimators compared, regardless of the number of loci, type of actual relationships, allele frequencies known or estimated from samples. Simulations also show that the confidence intervals estimated by bootstrapping are appropriate for different estimators provided that the number of loci used in the estimation is not small.

Computer Simulation↗

PubMed1998

Genotyping of 27 human papillomavirus types by using L1 consensus PCR products by a single-hybridization, reverse line blot detection method.

Amplification of human papillomavirus (HPV) DNA by L1 consensus primer systems (e.g., MY09/11 or GP5(+)/6(+)) can detect as few as 10 to 100 molecules of HPV targets from a genital sample. However, genotype determination by dot blot hybridization is laborious and requires at least 27 separate hybridizations for substantive HPV-type discrimination. A reverse blot method was developed which employs a biotin-labeled PCR product hybridized to an array of immobilized oligonucleotide probes. By the reverse blot strip analysis, genotype discrimination of multiple HPV types can be accomplished in a single hybridization and wash cycle. Twenty-seven HPV probe mixes, two control probe concentrations, and a single reference line were immobilized to 75- by 6-mm nylon strips. Each individual probe line contained a mixture of two bovine serum albumin-conjugated oligonucleotide probes specific to a unique HPV genotype. The genotype spectrum discriminated on this strip includes the high-risk, or cancer-associated, HPV genotypes 16, 18, 26, 31, 33, 35, 39, 45, 51, 52, 55, 56, 58, 59, 68 (ME180), MM4 (W13B), MM7 (P291), and MM9 (P238A) and the low-risk, or non-cancer-associated, genotypes 6, 11, 40, 42, 53, 54, 57, 66, and MM8 (P155). In addition, two concentrations of beta-globin probes allowed for assessment of individual specimen adequacy following amplification. We have evaluated the performance of the strip method relative to that of a previously reported dot blot format (H. M. Bauer et al., p. 132-152, in C. S. Herrington and J. O. D. McGee (ed.), Diagnostic Molecular Pathology: a Practical Approach, (1992), by testing 328 cervical swab samples collected in Digene specimen transport medium (Digene Diagnostics, Silver Spring, Md.). We show excellent agreement between the two detection formats, with 92% concordance for HPV positivity (kappa = 0.78, P < 0.001). Nearly all of the discrepant HPV-positive samples resulted from weak signals and can be attributed to sampling error from specimens with low concentrations (<1 copy/microliter) of HPV DNA. The primary advantage of the strip-based detection system is the ability to rapidly genotype HPVs present in genital samples with high sensitivity and specificity, minimizing the likelihood of misclassification.

Animals↗

PubMed1999

Evaluation of heterogeneity of DNA ploidy in early gastric cancers.

DNA ploidy has been shown to be a predictive parameter for prognosis in various solid tumours. The prognostic value of DNA-ploidy in gastric cancers is still a matter of controversy. A possible explanation for the discrepant results reported in the literature could be sampling error in tumours with multiple stemlines differing in DNA-ploidy. In order to determine whether or not such heterogeneity exists in early gastric carcinoma, we have performed DNA cytophotometry on multiple samples of a group of 17 early gastric carcinomas, of which 8 were pure intramucosal and 9 were infiltrating into the submucosa. We found an aneuploid DNA-stemline in 8 (47%) early gastric cancers, more often in tumours invading into the submucosa (5/9) than in purely mucosal tumours (3/8). Multiple DNA-stemlines were found more frequently in submucosally infiltrating tumours (4/5). These results confirm the presence of DNA-aneuploid early gastric carcinoma which are frequently heterogeneous and suggest that heterogeneity occurs more frequently in tumours invading the submucosa. This heterogeneity is best detected by analysing multiple samples of tumours for DNA-ploidy.

Adult↗

PubMed2001

On estimating the proportion of variance in a phenotypic trait attributable to a measured locus.

The measured genotype approach can be used to estimate the variance contributions of specific candidate loci to quantitative traits of interest. We show here that both the naive estimate of measured-locus heritability, obtained by invoking infinite-sample theory, and an estimate obtained from a bias-corrected variance estimate based on finite-sample theory, produce biased estimates of heritability. We identify the sources of bias, and quantify their effects. The two sources of bias are: (1) the estimation of heritability from population samples as the ratio of two variances, and (2) the existence of sampling error. We show that neither heritability estimator is less biased (in absolute value) than the other in all situations, and the choice of an ideal estimator is therefore a function of the sample size and magnitude of the locus-specific contribution to the overall phenotypic variance. In most cases the bias is small, so that the practical implications of using either estimator are expected to be minimal.

Bias↗

PubMed1990

Nonlinear forecasting as a way of distinguishing chaos from measurement error in time series.

An approach is presented for making short-term predictions about the trajectories of chaotic dynamical systems. The method is applied to data on measles, chickenpox, and marine phytoplankton populations, to show how apparent noise associated with deterministic chaos can be distinguished from sampling error and other sources of externally induced environmental noise.

Animals↗

PubMed2004

[Statistical models for spatial analysis in parasitology].

The simplest way to study the spatial pattern of a disease is the geographical representation of its cases (or some indicators of them) over a map. Maps based on raw data are generally "wrong" since they do not take into consideration for sampling errors. Indeed, the observed differences between areas (or points in the map) are not directly interpretable, as they derive from the composition of true, structural differences and of the noise deriving from the sampling process. This problem is well known in human epidemiology, and several solutions have been proposed to filter the signal from the noise. These statistical methods are usually referred to as Disease Mapping. In geographical analysis a first goal is to evaluate the statistical significance of the heterogeneity between areas (or points). If the test indicates rejection of the hypothesis of homogeneity the following task is to study the spatial pattern of the disease. The spatial variability of risk is usually decomposed into two terms: a spatially structured (clustering) and a non spatially structured (heterogeneity) one. The heterogeneity term reflects spatial variability due to intrinsic characteristics of the sampling units (e.g. igienic conditions of farms), while the clustering term models the association due to proximity between sampling units, that usually depends on ecological conditions that vary over the study area and that affect in similar way breedings that are close to each other. Hierarchical bayesian models are the main tool to make inference over the clustering and heterogeneity components. The results are based on the marginal posterior distributions of the parameters of the model, that are approximated by Monte Carlo Markov Chain methods. Different models can be defined depending on the terms that are considered, namely a model with only the clustering term, a model with only the heterogeneity term and a model where both are included. Model selection criteria based on a compromise between degree of complexity and goodness of fit are then needed to discriminate among them, because each specification has a different biological meaning. Our aim is to demonstrate that these techniques can be used to study the geographical distribution of a parasite infection. Our analyses are based on data collected in 142 farms of the province of Latina. In each breeding a fixed number of sheeps has been sampled (20) and checked for the presence of C. daubneyi. We have specified a Binomial model for the proportion of infected animals in each breeding. The heterogeneity component is modelled in a standard way, while we have used different prior specifications for the clustering term to show how they affect the results. When we use the usual specification also for clustering, the two models show a completely different spatial pattern of infection, probably because the intrinsic spatial structure of the clustering term tend to bias our inferences. The selection criterion indicates in this case the heterogeneity model as the "best" one. However, if we modify the prior so that a lower degree of spatial interaction is assumed, the clustering model is less complex and its goodness of fit better and it should be preferred.

Animal Husbandry↗

PubMed1990

Ultrastructural heterogeneity of lung carcinomas: representativity of samples for electron microscopy in tumor classification.

Histologic heterogeneity of tumors is a well-known phenomenon, which has been repeated studied at the light microscopic level. Electron microscopy has been advocated as an adjunct in classification of tumors which pose difficulties on light microscopic classification. However, in view of tumor heterogeneity, it might be anticipated that the problem of sample error could detract from the usefulness of electron microscopy in tumor typing. Ultrastructural heterogeneity of tumors has thus far not been systematically investigated. We performed an ultrastructural randomized and blinded study of superficial and deep samples of 44 resected lung carcinomas, tumors which are notorious for their histologic heterogeneity. Neuroendocrine and squamous differentiation, as well as adenodifferentiation, were assessed separately and semiquantitatively in each sample. Twenty-six tumors showed more than one type of differentiation in at least one sample. However, in only two cases did the main type of differentiation differ between the two samples. A further nine cases showed one predominant differentiation type in both samples, but a similarly pronounced second differentiation type in one of the samples. Thus, in terms of ultrastructural diagnosis, the two samples showed a major discrepancy in two of 44 cases, and a minor discrepancy in nine of 44 cases. We conclude that ultrastructural heterogeneity of lung tumors is a common occurrence, but that it only rarely leads to totally different ultrastructural diagnoses.

Carcinoma↗

PubMed1995

Accuracy of frozen section diagnosis in surgical pathology: review of a 1-year experience with 24,880 cases at Mayo Clinic Rochester.

OBJECTIVE: To determine the accuracy of frozen section examination for routine diagnostic use in surgical pathology. DESIGN: We retrospectively reviewed the experience with frozen sections at Mayo Clinic Rochester during calendar year 1993. MATERIAL AND METHODS: The results in 24,880 cases (97,914 frozen section slides) processed during 1993 were compared with findings on permanent sections, and types of errors detected were classified into one of three quality assurance categories. RESULTS: The overall rate of frozen section accuracy was 97.8%. Of the 2.2% of surgical pathology reports that needed revision, 1.6% were unavoidable tissue sampling errors, 0.5% were errors that reflected change in degree of abnormality, and only 0.1% were clinically significant errors that may have affected patient management. CONCLUSION: Frozen section diagnosis is accurate for processing a high volume of surgical pathology cases.

Biopsy↗

PubMed1984

Myocarditis and endomyocardial biopsy.

There is little correlation between the clinical and the biopsy tissue diagnoses of myocarditis, and both are prone to false-positive and false-negative interpretations. Perhaps the most common error that leads to a false-positive clinical diagnosis of myocarditis is the preconceived but unproved notion that unexplained heart failure of sudden onset or rapid progression must be due to myocarditis. Therefore, most clinical diagnoses of myocarditis are presumptive and are never proved "beyond all reasonable doubt." False-negative clinical diagnoses may occur in patients with myocarditis in whom signs and symptoms are atypical or absent. The two most common sources of error that result in a false-positive biopsy tissue diagnosis of myocarditis are a failure to recognize how many lymphocytes normally occupy the myocardial interstitium and a misinterpretation of noninflammatory interstitial cells as lymphocytes. Sampling error may be the most common cause of false-negative tissue diagnoses in patients with myocarditis. Myocarditis is characterized histologically by an inflammatory infiltrate and by injury to myocardial cells that is not typical of infarction. Healing may occur by resolution or fibrosis. I believe that quantitative evidence of an interstitial leukocytic infiltrate is currently the best histopathologic criterion for the diagnosis of myocarditis in biopsy tissue. In the setting of clinically suspected myocarditis, the tissue diagnosis of myocarditis in a patient's first biopsy should be designated as present, borderline, or absent. In subsequent biopsies, the myocarditis should be evaluated in a temporal as well as a qualitative or quantitative sense and designated as ongoing, resolving, or resolved. The nature of the inflammatory infiltrate and the extent of fibrosis should also be stated in all such biopsies. The pathologist should render an evaluation that is as accurate and unbiased as possible, since patients with a tissue diagnosis of myocarditis often receive immunosuppressive therapy that may have associated morbidity or even mortality.

Biopsy↗

PubMed2002

Estimation of the homogeneity of reference materials by SS-ETAAS and use of the "tape-sandwich" sample-introduction technique.

The so called "tape sandwich", a novel sample-introduction technique developed for SS-ETAAS, has been employed in a study of the microheterogeneity of some biological CRM. Pb, Cd, and Cr were measured by use of a laboratory-assembled instrument with graphite-cup atomizer. Aqueous standards were found satisfactory for calibration. The average mass of sub-samples atomised was in the range 0.250-0.660 mg+/-30%. The relative sampling error found for the CRM investigated varied from 15-34%. Calculated relative homogeneity constants of the order of 4-21 mg(1/2) were obtained, and were reduced considerably by reduction of the particle size. The minimum sample sizes representative of the CRM were, with one exception, much lower (11-75 mg) than those recommended in the documentation accompanying the standards (100-200 mg). In a Chinese hair reference sample Cr data were normally distributed but the presence of nuggets was observed for Cd and Pb; this was associated with severe radial and longitudinal gradients of these elements in hair.

Cadmium↗

PubMed2001

[Simplifying the sampling method for evaluating the larval density of Aedes aegypti in São Paulo State, Brazil].

OBJECTIVE: To suggest changes in the sampling procedures for estimating the larval density of Aedes aegypti in the state of São Paulo, Brazil, by assessing the efficacy and level of complexity of the current procedures. METHODS: The "Superintendência de Controle de Endemias do Estado de São Paulo" - SUCEN's (Superintendence for Endemic Control of the State of São Paulo) sampling procedures for estimating the density of Aedes aegypti larvae was assessed. The Breteau index with one-stage cluster sampling was applied. An average of 35 blocks, 14 buildings per block, of a total of 510 buildings per sample, were assessed. One hundred and eleven samples were obtained in 6 municipalities of São José do Rio Preto. RESULTS: The Breteau index estimates higher than 3 had coefficients of variation smaller than 30% in 71% of the samples. The design effect was 1.19 and 1.79 for indexes lower and higher than 5, respectively. The estimates were obtained in less than 3 days, requiring a daily average of 5.5 men per sampling. CONCLUSION: This sampling design revealed to be a simplified one: fast, economic and easily managed. The operational easiness was due to the use of the one-stage cluster sampling, when there was not need to prepare lists of addresses and then sort and locate the buildings. Though the design effect shows a slight loss of the estimates' accuracy with the use of one-stage cluster sampling, this was proven to be under acceptable range. Simplifying changes in the process of determining the sample size and assessing sampling errors are proposed.

Aedes↗

PubMed2001

Model selection and parameterization of the concentration-response functions for population-level effects.

As concentration response functions for chronic population-level effects of pollutant chemicals, three mathematical models were presented and examined for goodness of fit to published toxicological data that estimated the population-level effects of chemicals in terms of the intrinsic rate of population growth (r). Among the examined concentration-r functions, the power function model, that is, r(x) = r(0)[1 - (x/alpha)beta], in which x is the exposure concentration and alpha and beta are parameters, performed with the best fit to each data set. The power function model is characterized by two parameters representing the absolute value of toxicity, alpha, and the curvature of responses, beta. The bootstrap simulation, conducted on the entire data set consisting of all published data that we collected, indicated that the observed variance of beta among actual data sets could be mostly explained by the random error variation generated from the bootstrap resamplings. The generic beta value, determined from the entire data set and expected to denote the best estimate of beta if the variability of beta was completely due to random sampling error, was estimated as 1.84. It was implied that the response of the intrinsic rate of natural increase (r) to chemical exposure was nearly quadratic in many cases.

Animals↗

PubMed1985

Current problems in establishing quantitative histopathologic criteria for the diagnosis of lymphocytic myocarditis by endomyocardial biopsy.

Both the clinical and the biopsy diagnoses of myocarditis are prone to false-positive and false-negative interpretations. False-positive clinical diagnoses probably most commonly result from a failure to recognize other disorders, such as cardiomyopathy and myocardial infarction, that may mimic myocarditis. False-negative clinical diagnoses may occur in patients with myocarditis in whom the signs and symptoms are atypical, absent, or misinterpreted. The two most common errors made by pathologists that produce false-positive tissue diagnoses appear to be a failure to recognize the number of lymphocytes that occupy the normal myocardial interstitium and a misinterpretation of noninflammatory interstitial cells as lymphocytes. Sampling error may be the most usual cause of false-negative tissue diagnoses. Since myocarditis is characterized by leukocytic and reparative responses, the most important features to evaluate in endomyocardial biopsy tissues are the type, distribution, and extent of the inflammatory infiltrate and the presence and extent of interstitial and endocardial fibrosis. Although no single histopathologic criterion is both sensitive and specific for myocarditis, it appears that quantitative evidence of an interstitial leukocytic infiltrate is currently the best available hallmark for myocarditis in biopsy specimens. It is suggested that a mean lymphocyte count greater than 5.0/high-power (X 400) microscopic field be considered indicative of lymphocytic myocarditis and that a mean count less than this be interpreted as myocarditis only if discrete clusters of lymphocytes are identified, since differentiation of low-grade diffuse infiltrates from expected normal lymphocytic populations is problematic at levels less than 5.0.

Biopsy↗

PubMed1976

Variation and control of specific antigen-binding cell populations in individual fetal mice.

To determine the extent and nature of individual variation in the development of specific antigen-binding cells, the numbers of cells specific for each of two antigens in the spleens of individual random-bred Swiss-L and inbred CBA/J and BALB/c fetal mice were measured as a function of spleen size. For Swiss-L fetuses, the ratio of antigen-binding cells to nucleateated cells varied more than would arise from sampling fluctuation. For each inbred strain, however, the number of cells specific for a given antigen was a constant proportion of the total number of nucleated cells within sampling error. These proportions varied from antigen to antigen, and from strain to strain. The ratio of the proportions of cells specific for the two antigens, however, differed no more from CBA/J to BALB/c mice than would be expected in repeated samples of cells from the spleen of a single fetus. These results confirm at the level of the individual fetus the uniform pattern of development seen for populations of fetuses. They reveal a surprising precision in the proliferation of specific antigen-binding cell populations and suggest that the development of these cells may be subject to strong genetic controls.

Animals↗

PubMed2005

Profiles of pain in Mississippi: results from the Southern Pain Prevalence Study.

OBJECTIVES: To estimate the prevalence, intensity, frequency, and origins of pain in Mississippi residents and explore the social and cultural aspects of pain and pain management by measuring the impacts of pain on everyday life as well as respondents' beliefs and attitudes toward pain. STUDY DESIGN: Cross-sectional survey of Mississippi adults. SUMMARY OF BACKGROUND DATA: Data from previous population surveys and clinical studies indicate that pain is a pervasive part of everyday life. The prevalence, intensity and frequency of reported pain is substantial throughout these studies. The literature documents large and profound consequences of pain both for individual lives and for society. The data also suggest that beliefs and attitudes rooted in the social and cultural context of society may help explain how pain is managed or endured. METHODS: Telephone interviews with a representative sample (random digit dialing) of 604 Mississippi adults were conducted utilizing a computer-assisted telephone interviewing system. The cooperation rate was 94.8% (5.2 % refusal). The Code of Standards and Ethics for Survey Research rate was 67.4% and the maximum sampling error was +/- 4.0% (95% confidence interval). The Mississippi survey data represent a subset of the data obtained in the six-state Southern Pain Prevalence Study. RESULTS: The pain prevalence rate was estimated to be 37% of the overall Mississippi sample: 9% of the sample reported severe pain on at least a monthly basis; 16% reported moderate pain; and 12% reported mild pain. Among those reporting pain, a majority (52%) experienced pain on a daily basis. The most commonly reported origins of pain were back pain (49%), leg and knee pain (41%), and shoulder.and arm pain (20%). Respondents also reported that both moderate and severe pain had substantial negative impacts on multiple facets of everyday life, including interference with sleep (84%), recreational/leisure activities (78%), ability to work (68%), sexual relations (43%), and relationships with others (36%). Mental health impacts for respondents with moderate to severe pain on at least a monthly basis included increased feelings of anxiety (66%), self-reported depression (63%), and loneliness (46%). When responding to questions regarding beliefs and attitudes about pain and pain management, the majority of respondents (62%) considered pain to be a normal part of everyday life. Many respondents felt that medicine should be saved until the pain becomes worse (55%), and a substantial number of respondents felt that good patients do not complain about pain to their doctors (22%). CONCLUSIONS: This study expands the body of knowledge about the prevalence of pain in Mississippi, suggesting that approximately one-third of the state's adults are affected by pain on at least a monthly basis. Most of this pain is moderate to severe and quite frequent--occurring daily for the majority of pain sufferers. The study also illuminates social and cultural dimensions of pain, revealing that a) the presence of pain negatively affects almost every facet of life, from sleep and work to relationships, leisure activities, and mental health, and b) respondents attitudes and beliefs are often at variance with modern approaches to pain management. Knowledge gained could have critical implications for understanding patients and the treatment of pain.

Adolescent↗

PubMed2002

Positron emission tomography imaging of brain tumors.

A wide variety of metabolic features of brain tumors can be imaged using PET, including glucose metabolism, blood flow, oxygen consumption, amino acid metabolism, and lipid synthesis. Currently, FDG is the most widely available PET tracer for body imaging and brain imaging. Malignant brain tumors, like many other soft tissue tumors, show increased glucose metabolism, which is reflected on FDG-PET imaging. FDG-PET imaging of brain tumors provides information on tumor grade and prognosis. Compared with other organ systems, FDG-PET imaging of the brain presents unique challenges because of the high background glucose metabolism of normal gray matter structures. Coregistration of the MRI (or CT) and FDG-PET images is essential for accurate evaluation of brain tumors and is performed routinely at the authors' institution. The heterogeneous nature of gliomas can result in significant sampling errors when patients are biopsied for primary tumor diagnosis or recurrent disease. FDG-PET can be used to define the most metabolically active targets for stereotactic biopsy. This in turn can improve diagnostic accuracy and reduce the number of biopsy samples required. FDG-PET is also useful for evaluating residual or recurrent tumor following therapy, and can be used to survey patients with low-grade brain tumors for evidence of degeneration into high-grade malignancy. In the case of suspected tumor recurrence or progression, PET can aid in defining appropriate targets for biopsy. One limitation of FDG-PET is the occasional inability to distinguish radiation necrosis from recurrent high-grade tumor. A second limitation is that FDG-PET is less sensitive than contrast-enhanced MRI for detecting intracranial metastases, and it is the authors' experience that brain studies should not be included as part of routine whole-body PET studies. Other tracers, such as 11C-methionine and FCH, also avidly accumulate in brain tumors and have the advantage of low background cortical activity. The relationship between degree of uptake of these agents and tumor grade is not established. These tracers may be useful in specific clinical situations, however, such as tumor localization for treatment planning or evaluation of low-grade tumors.

Blood Volume↗

PubMed2005

Application of Bayesian inference using Gibbs sampling to item-response theory modeling of multi-symptom genetic data.

Several "genetic" item-response theory (IRT) models are fitted to the responses of 1086 adolescent female twins to the 33 multi-category item Mood and Feeling Questionnaire relating to depressive symptomatology in adolescence. A Markov-chain Monte Carlo (MCMC) algorithm is used within a Bayesian framework for inference using Gibbs sampling, implemented in the program WinBUGS 1.4. The final model incorporated separate genetic and non-shared environmental traits ("A and E") and item-specific genetic effects. Simpler models gave markedly poorer fit to the observations judged by the deviance information criterion (DIC). The common genetic factor showed major loadings on melancholic items, while the environmental factor loaded most highly on items relating to self-deprecation. The MCMC approach provides a convenient and flexible alternative to Maximum Likelihood for estimating the parameters of IRT models for relatively large numbers of items in a genetic context. Additional benefits of the IRT approach are discussed including the estimation of latent trait scores, including genetic factor scores, and their sampling errors.

Adolescent↗