Multiple imputation for missing continuous and dichotomous data: The effects of patterns of missingness and variable correlations on type I error with small samples

The purpose of this study is to investigate the effects of predictor variable correlations and patterns of missingness with dichotomous and/or continuous data in small samples when missing data is multiply imputed. Missing data of predictor variables is multiply imputed under three different multivariate models: the multivariate normal model for continuous data, the multinomial model for dichotomous data and the general location model for mixed dichotomous and continuous data. Subsequent to the multiple imputation process, Type I error rates of the regression coefficients obtained with logistic regression analysis are estimated under various conditions of correlation structure, sample size, type of data and patterns of missing data. The distributional properties of average mean, variance and correlations among the predictor variables are assessed after the multiple imputation process. ^ For continuous predictor data under the multivariate normal model, Type I error rates are generally within the nominal values with samples of size n = 100. Smaller samples of size n = 50 resulted in more conservative estimates (i.e., lower than the nominal value). Correlation and variance estimates of the original data are retained after multiple imputation with less than 50% missing continuous predictor data. For dichotomous predictor data under the multinomial model, Type I error rates are generally conservative, which in part is due to the sparseness of the data. The correlation structure for the predictor variables is not well retained on multiply-imputed data from small samples with more than 50% missing data with this model. For mixed continuous and dichotomous predictor data, the results are similar to those found under the multivariate normal model for continuous data and under the multinomial model for dichotomous data. With all data types, a fully-observed variable included with variables subject to missingness in the multiple imputation process and subsequent statistical analysis provided liberal (larger than nominal values) Type I error rates under a specific pattern of missing data. It is suggested that future studies focus on the effects of multiple imputation in multivariate settings with more realistic data characteristics and a variety of multivariate analyses, assessing both Type I error and power. ^

The association of sexual behavior with oropharyngeal cancer and correlations with HPV-16 serologic status

Objectives. This hospital-based case-case study compared the characteristics of sexual behavior in patients with cancer of the oropharynx to patients with cancers of other head and neck sites. Additionally, the prevalence of certain sexual behaviors of HPV-16 seropositive head and neck cancer patients was compared to that of seronegative patients. ^ Methods. One hundred sixty five oropharyngeal cancer patients and 86 patients with cancers of other head and neck sites completed a sexual history questionnaire. ^ Results. Oropharyngeal cancer patients were significantly more likely to have had a greater number of lifetime sex partners, to have engaged in oral-genital sex, and to have had a greater number of oral-genital sex partners than non-oropharyngeal cancer patients. Oral-genital sex was significantly more common in the HPV-16 seropositive group. ^ Conclusion. These findings add to the evidence that HPV-16 is sexually transmitted to the upper aerodigestive tract and that certain sexual behaviors increase the risk for HPV-associated oropharyngeal cancer. ^

Behavioral responses to methylphenidate: correlations with neuronal activity in the caudate nucleus

Methylphenidate is currently a drug of abuse and readily prescribed to both adolescents and adults. Chronic methylphenidate (MPH) exposure results in an increase in DA in the motive circuit, including the caudate nucleus (CN), similar to other drugs of abuse. This study focuses on research aimed to elucidate if there are intrinsic underlying differences in the CN electrophysiological activity of animals exhibiting different chronic responses to the same dose of MPH. Behavioral and caudate nucleus (CN) neuronal activity following acute and chronic doses of MPH was assessed by simultaneously recording the behavioral and neuronal activity. The experimental protocol lasted for 10 days using four groups; saline, 0.6, 2.5 and 10.0mg/kg MPH. Initially, the study determined that animals exposed to the same dose of MPH exhibited either behavioral sensitization or behavioral tolerance. Therefore animals were classified into two groups (behaviorally sensitized/tolerant) and their neuronal activity was evaluated. Four hundred and fifty one units were evaluated. Overall, a mixture of increases and decreases in CN neuronal populations was observed at initial MPH exposure, and at ED10 baseline and ED10 rechallenge. When separated based on their behavioral response (sensitized/tolerant), significant differences in neuronal response patterns was revealed. Animals exhibiting sensitization were more likely to increase their neuronal activity at ED1 and ED10 baseline, expressing the opposite response at ED10 rechallenge. Furthermore, when neuronal populations recorded from those animals exhibiting behavioral sensitization were statistically compared to those from animals exhibiting behavioral tolerance significant differences were observed. Collectively, these findings tell us that animals exposed to the same dose of MPH can respond oppositely and moreover that there is in fact some intrinsic difference in the two population’s neuronal activity. This study offers new insight into the electrophysiological differences between sensitized and tolerant animals.