Specification of Variance-Covariance Structure in Bivariate Mixed Model for Unequally Time-Spaced Longitudinal Data

In medical studies, the longitudinal data sets obtained from more than one response variables and covariates are mostly analyzed to investigate the change in repeated measurements of each subject at different time points. In this study, the usability of multivariate models in the analysis of these kind of data sets is investigated, because it provides the joint analysis of multiple response variables over time and enables researchers to examine both the correlations of response variables and autocorrelation between measurements from each response variable over time. It has been shown that different parameter estimation methods affect the results in the analysis of multivariate unbalanced longitudinal data. We investigated that autocorrelation structure over time between measurements from same response variable should be truly specified. We also illustrated and compared the simpler, more standard models for fixed effects with multivariate models provided by SAS on a real-life data set in the joint analysis of two response variables. Results show that misspecification of autocorrelation structures has a negative impact on the parameter estimates and parameter estimation method should become of interest

Reliability and Validity of the Turkish Version of the Glasgow-Edinburgh Throat Scale: Use for a Symptom Scale of Globus Sensation in Turkish Population

Objective: In this study, we aimed to translate the Glasgow-Edinburgh Throat Scale (GETS) into Turkish and test its reliability and validity.Methods: A total of 69 patients with globus sensation and no signs of otolaryngologic or gastroenterological disease in etiology were included in the study. The patients were asked to complete the translated Turkish version (GETS-T) of GETS and the Hospital Anxiety and Depression Scale (HADS).Results: The Cronbach’s alpha coefficient of the patients in the study group was calculated based on the 12 questions in the GETS-T scale and found as 0.868. The correlation between the GETS-T total score and the total HADS score in the study group was found to be very low and statistically insignificant. As a result of factor analysis, it was found that the first 10 problems in GETS-T were divided into two sub-groups, unlike GETS.Conclusion: Translation of GETS into Turkish (GETS-T) showed high reliability and validity, suggesting that translation and cross-cultural adaptation was appropriate. The GETS-T can be used in studies about globus pharyngeus in future

APPROACH TO CUTANEOUS LESIONS OF THE HEAD AND NECK IN THE GERIATRIC AGE GROUP: RETROSPECTIVE ANALYSIS OF 170 CASES

Introduction: The incidence of skin lesions increases with advancing age, especially in the head and neck region. The aim of this study was to evaluate the demographic data of head and neck skin lesions in the geriatric age group and the preferred surgical approaches. Material-Method: The records of 170 patients of an age >65 years who underwent surgical excision and reconstruction for head and neck lesions in our clinic were retrospectively reviewed. The histopathological results of the lesions and the repair method used were evaluated according to age and localization. Results: The mean age of the patients was 71.42 ± 14.20 years. The histopathologic distribution of the lesions were 75 (44.2%) basal cell carcinoma, 30 (17.6%) squamous cell carcinoma and 65 (38.2%) benign. The most frequent localizations were nose and cheeks, and the most preferred reconstruction methods were primary closure and advancement flap. None of the patients had serious complications. Conclusion: Basal cell carcinoma is the most common lesion in the head and neck region in elderly individuals. The lesions in this region can be detected in the early stage since they are in the visible region. The Surgical excision and repair with local flaps in the treatment provide very successful cosmetic results

Analysing outcome variables with floor effects due to censoring: a simulation study with longitudinal trial data

ackground: Randomised controlled trials (RCTs) are the gold standard to estimate treatment effects. When patients receive effective treatment over time they may reach the limit of a certain measurement scale. This phenomenon is known as censoring and lead to skewed distributions of the outcome variable with an excess of either low (floor effect) or high values (ceiling effect). Applying traditional methods such as linear mixed models to analyse this kind of longitudinal RCT data may result in bias of the regression parameters. To deal with floor effects due to censoring,  a tobit mixed model can be used. The objective of this study was to compare the results of longitudinal linear mixed model analyses with longitudinal tobit mixed model analyses.Methods: First, a simulation study was performed in which several situations of RCTs with floor effects were simulated. Second, data from an empirical RCT was analysed with both methods.Results: Although all analyses underestimated the intervention effects, the tobit mixed model performed much better than the linear mixed model in handling floor effects. However, with an increasing number of follow-up measurements in combination with a strong floor effect estimates from the tobit mixed model were also not accurate.Conclusion: tobit mixed model analysis should be used to estimate treatments effects in longitudinal RCTs with floor effects due to censoring.&nbsp

Uzun Süreli Çalışmalarda Ma(1) ve Arma(1,1) Otokorelasyonlu Hatalara Sahip Doğrusal Karma Etkiler Modelleri için Örneklem Büyüklüğünün Belirlenmesi

The aim of the study is to determine sample sizes for the number of subjects and the number of repeated measures for a Linear Mixed Effects Model (LMM) with random intercept and slope in the analysis of longitudinal data set with first order moving average (MA(1)) or first order autoregressive moving average (ARMA(1,1)) autocorrelated errors. In this study, for this reason, a Monte Carlo (MC) simulation approach, which compute statistical power for LMM with random intercept and slope in the analysis of longitudinal data set with MA(1) or ARMA(1,1) autocorrelated errors, was developed by means of SAS 9.1 statistical program and according to assumptions in simulation studies, for the number of subjects and the number of repeated measures, sample sizes based on statistical power were calculated. At the end of the study, it was concluded that the conditions controlled by researchers, like the structure of LMM with random intercept and slope, the number of subjects, the number of repeated measures, the autocorrelation coefficient and a hyphothesis test on parameter interested in model, affected the statistical power and sample sizes calculated based on statistical power were changing.Tez çalışmasının amacı, birinci dereceden hareketli ortalama (MA(1)) veya birinci dereceden karma otoregresif hareketli ortalama (ARMA(1,1)) yapısındaki otokorelasyonlu hatalara sahip uzun süreli çalışmaların analizinde kullanılan Rastgele Kesim Noktalı ve Eğimli Doğrusal Karma Etkiler Modeli (RKE-DKEM) için çalışmaya katılacak birim sayısı ve birimlerden alınacak tekrarlı ölçüm sayısı için örneklem büyüklüklerini hesaplamaktır. Tez çalışmasında, bu amaçla, SAS 9.1 istatistiksel yazılım programı yardımıyla, MA(1) veya ARMA(1,1) otokorelasyonlu hatalara sahip uzun süreli veri kümesinin analizinde kullanılan RKE-DKEM‘leri için istatistiksel güç hesaplayan bir Monte Carlo (MC) simülasyon yaklaşımı geliştirilmiş ve istatistiksel güce dayanarak, simülasyon çalışmalarında yapılan varsayımlara göre, birim sayısı ve birimlerden alınan tekrarlı ölçüm sayısı için örneklem büyüklükleri hesaplanmıştır. Tez çalışmasının sonunda, RKE-DKEM‘nin yapısının, otokorelasyon katsayısının, uzun süreli çalışmaya katılan birim sayısının, birimlerden alınan tekrarlı ölçüm sayısının ve model parametresi üzerine kurulu hipotez testi gibi araştırmacı tarafından kontrol edilebilen koşulların istatistiksel gücü etkilediği ve istatistiksel güce bağlı olarak hesaplanan örneklem büyüklüklerinin değiştiği görülmüştür

Management of renin-angiotensin-aldosterone inhibitors and other antihypertensives and their clinical effects on pre-anesthesia blood pressure

Background Blood pressure fluctuations appear more significant in patients with poorly controlled hypertension and are known to be associated with adverse perioperative morbidity. In the present study, we aimed to determine the effects of antihypertensive drug treatment strategies on preanesthetic operating room blood pressure measurements. Methods A total of 717 patients participated in our study; 383 patients who were normotensive based on baseline measurements and not under antihypertensive therapy were excluded from the analysis. The remaining 334 patients were divided into six groups according to the antihypertensive drug treatment. These six groups were examined in terms of preoperative baseline and pre-anesthesia blood pressure measurements. Results As a result of the study, it was observed that 24% of patients had high blood pressure precluding surgery, and patients using renin-angiotensin-aldosterone system inhibitors (RAASI) had higher pre-anesthesia systolic blood pressure than patients using other antihypertensive drugs. Patients who received beta-blockers were also observed to have the lowest pre-anesthesia systolic blood pressure, diastolic blood pressure, and mean blood pressure, compared to others. Conclusions Recently, whether RAASI should be continued preoperatively remains controversial. Our study shows that RAASI cannot provide optimal pre-anesthesia blood pressure and lead to an increase in the number of postponed surgeries, probably due to withdrawal of medication before the operation. Therefore, the preoperative discontinuation of RAASI should be reevaluated in future studies

Cerrahi Tekniğin Uterin Fibroidlerin Psödokapsülü Üzeindeki Etkisi: Ön Sonuçlar

Amaç: Leiomyomlar kadın genital sisteminin en sık görülen iyi huylu tümörleridir. Myomektomi, fertiliteyi korumak için iyi bir seçenektir. Myomektomi, hem laparotomi (LT) hem de laparoskopi (LS) ile yapılabilmektedir. LS’de LT’ye göre psödokapsül liflerinin daha iyi korunduğu düşünülmektedir. Psö- dokapsülün korunması myometriumun sonraki fonksiyonelli ği için önemlidir. Bu çal ışmada LS ve LT myomektomi yap ılmış olgularda, myomektomi spesmenlerinin myom psödokapsül kalınlıklarını karşılaştırmayı amaçladık. Gereç ve Yöntemler: Ufuk Üniversitesi Tıp Fakültesi Kadın Hastalıkları ve Doğum Kliniği’nde Ocak 2018 ve Aral ık 2018 tarihleri arasında myomektomi yapılmış olan 121 hasta kaydından 34’ü zarf yöntemiyle seçilerek retros- pektif olarak incelenmiştir. Kayıtlar; hastaların yaşları, vücut kitle indeksleri (VKİ), myomektomi endikasyonları, myom sayıları, myom çapları ve geçi- rilmiş abdominal cerrahi için tarand ı. Laparoskopik ve laparotomik myomektomi gruplar ı psödokapsül kalınlığı açısından karşılaştırıldı. Bulgular: Çalışmaya toplam 34 hasta dahil edildi. Bu hastalar ın 20’sine LT myomektomi (%58.8), 14’üne LS myomektomi (41.1%) yap ılmıştı. LT ve LS myo- mektomi grupları arasında hasta ya şı, VKİ bakımından istatistiksel aç ıdan anlamlı fark izlenmedi. Myomektomi endikasyonlar ının dağılımı da gruplar arasında benzerdi. Geçirilmiş abdominal cerrahisi olan hastaların oranı LT myomektomi grubunda, LS grubuna göre yüksekti (40.0% vs 7.1%; p:0.049, sırasıyla). Psödokapsül kalınlıkları, LT grubunda LS grubuna göre anlamlı olarak yüksekti (1.2 vs 0.75, p:0.013).Sonuç: Bu çalışma LT myomektomi yön- teminde eksize edilen psödokapül kalınlığının LS’ye göre artmış olduğunu ve laparoskopide psödokapsülün daha yüksek oranda korunduğunu göstermiş- tir. Psödokapsülün korunmasının, post-operatif myometrial iyileşme ve bütünlük üzerindeki olumlu etkilerini doğrulayan daha geniş örneklem büyüklüğüne sahip prospektif çalışmalar gerekmektedir

Analysing outcome variables with floor effects due to censoring:A simulation study with longitudinal trial data

Background: Randomised controlled trials (RCTs) are the gold standard to estimate treatment effects. When patients receive effective treatment over time they may reach the limit of a certain measurement scale. This phenomenon is known as censoring and leads to skewed distributions of the outcome variable with an excess of either low (floor effect) or high values (ceiling effect). Applying traditional methods such as linear mixed models to analyse these kind of longitudinal RCT data may result in bias of the regression coefficients. To deal with floor effects due to censoring, a tobit mixed model can be used. The objective of this study was to compare the results of longitudinal linear mixed model analyses with longitudinal tobit mixed model analyses. Methods: A simulation study was performed in which several situations of RCTs with floor effects were simulated. From the simulated datasets, which were set up to estimate the interaction between treatment and time, the regression coefficient for this interaction and for the overall treatment effect were estimated. Additionally, data from an empirical RCT were analysed with both methods. Results: Regarding the interaction between treatment and time, the results of the tobit mixed model analysis were the same as the true values in all conditions, while the linear mixed model analysis revealed highly underestimated regression coefficients. However, the overall treatment effect with an increasing number of follow-up measurements in combination with a strong floor effect showed that the estimates from the tobit mixed model were also not accurate. Conclusion: Tobit mixed model analysis should be used to estimate treatments effects in longitudinal RCTs with floor effects due to censoring