The method of selection of the study design decides the type of analysis 10 be used. Case-Control studies assess the causes of a particular outcome, comparing a group of individuals who have experienced the outcome under study with a group who have net.Results appear as a two by two table. As these two groups are sampled separately, the rate of the disease in the exposed or unexposed groups can not be calculated. However, the Odds Ratio can be obtained. The Odds Ratio is sometimes referred to as the cross product ratio.                        Cases                            Controls Exposed            a                                  b Unexposed         c                                  d Odds Ratio (a/b)I (c/d) = ad/bc

Relative risk (RR) and Odds ratio (OR) are two measures of risk which has been widely used in epidemiological studies. The cohort studies are designed to directly compute a relative risk, but the situation is somewhat more complicated in the case-control design. In these studies, the odds ratio gives a valid estimate of the effect size. There is not a serious problem if you don’t use of the odds ratio as an estimator of relative risk, but the problem begins when the odds ratio used as a surrogate for relative risk while its meaning is forgotten as the ratio of tow odds. The author has tried, to describe the relationship between relative risk and odds ratio and also the right time to use each of theme for those who familiar with the basic concept of epidemiologic studies. In this paper, the concepts of probability and chance and definitions refer to relative risk and odds ratios and characteristics of each have been reported. Afterward the gaps between RR and OR according to their computational formulas are described and a simple method to estimate the OR to RR ratio is expressed.

DEAR EDITOR, This is regarding the article published in your journal "Diabetes and Oral Health: A Case-control Study" Vol. 3, No. 11, November 2012.I appreciate the efforts by the author for making excellent study in diabetes and much neglected part of it, oral health.

Background: Obesity is becoming a world wide health problem, affecting all groups of age, sex and economy. This important problem is a major risk factor for some diseases. The prevalence of obesity not has been well studies in the rural areas. The purpose of this study was to determine the prevalence of obesity and some of the relevant risk factors in women of Zarrindasht rural areas using the odds ratio estimated from the regression approach.Methods and Materials: In a cross-sectional study in 2005, a number of920 women infertility age from rural areas of Zarrin-Dasht, at eastern part of Fars province were selected by random multi stage sampling. Correlation ship between BMI and some variables including age, education level, number of children, socio-economic status and mean duration of breast feeding were evaluate. The age and education level of their husbands were also considered. Odds ratio (OR) was using both logistic regression approach and the linear regression procedure (without dichotomizing). BMI of 25 or higher was considered as over weight or obesity. Results: The studied women aged between 17 to 47 years old and the prevalence of over weight (25<BMI<30) and obesity (BMI³30) was 30% and 14% respectively. In both statistical models, significant associations were found among husbands education, number of children, socioeconomic status and increasing risk of obesity. Precision of linear regression approach in estimating OR was higher than that of logistic regression.Conclusions: It is concluded that, similar to the urban areas, the obesity is highly prevalent in the rural population. This can potentially affect the health of rural community and needs consideration.Prevention and control of obesity are recommended to be as of health program priorities.

Dear Editor: We read with interest the article by Abu El Makarem MA et al. (1) entitled, “Platelet count/bipolar spleen diameter ratio for the prediction of esophageal varices: The special Egyptian situation.” This study evaluated noninvasive predictors of esophageal varices in cirrhotic patients by multivariate logistic regression and receiver operating characteristic (ROC) curve analysis. However, in our opinion, some aspects of the statistical analysis could be clarified. The first issue concerns the ROC analysis.The full area under the ROC curve (AUC) is a measure of the performance of the diagnostic test because it reflects the test performance at all possible cutoff levels.The AUC lies in the interval [0.5, 1], and the larger area, the better performance. A perfect test has an AUC of 1.0, whereas random chance gives an AUC of 0.5 (2, 3). In Abu El Makarem MA et al.’s paper, the AUC for age is 0.33, which is less than 0.5. Therefore, we think that something might have gone wrong when the authors performed the ROC analysis with the SPSS software. Because both the univariate analysis and multivariate logistic regression identified age as a valuable predictor of varices, older patients experienced a higher risk having varices. We presume that the AUC for age may be 0.67 (1-0.33) rather than 0.33. The second issue has to do with the odds ratio. The odds ratio refers to a ratio of the odds of the outcome occurring in one group divided by the odds of the outcome occurring in the other group with a 1-unit increase in x (4). The odds ratio for age was 1.205 in Abu El Makarem MA et al.’s (1) paper, but no statement such as “for a one year increase in age” was mentioned.

Background: The role of psychological factors related to migraine headache has been a focus of investigation for long time. The purpose of this study was to determine relationship between marital conflicts as important stress source and migraine headache.Methods: In order to evaluate marital conflicts among patients with migraine and to compare with control group, 74 patients with migraine according to International Headache Society (IHS) criteria, were randomly selected from Clinic of Neurology in Alzahra Medical Center. Control group were matched base on some of patients demographic characters, and selected from medical and health centers. Both groups were assessed by Iranian version of Marital Conflicts Questionnaire. Data was analyzed by Manwithny U, Pearson and two point serials correlations and logistic regression Methods.Findings: Data revealed that frequency of marital conflicts among patients with migraine (28%) was higher than control group (11%). Mean score of Marital Conflict was higher in patients than control group (p<0.01). Migraine headache was predictable based on marital conflicts scores, positive family history and education.Conclusion: Chronic stress and lack of qualified skills to cope with stress may be precipitate migraine headache. Because migraine is multifactorial disorder, it is necessary to suggest psychological variables in treatment plan, so couple therapy and skill learning to strengthen the family relations for patients are recommended.

Background and aim: Dysfunctional attitude may be predispose factor for depression, but there are few investigations for that. The aim of this study was to determine contributions of dysfunctional attitude and general health index based on GHQ-28 to depression.Methods: In this description and analytical study, a total of 65 patients with major depression and dythymic disorder from Noor and Navab-Safavi psychiatry clinics and 65 healthy individuals with age and sex, and education matched were randomly selected. Dysfunctional attitude scale and general health questionnaire were filled in by two groups. Data were analyzed using linear and logistic regression and correlation methods.Results: Logistic regression analysis on categorized scores of DAS- 26 as high and low risk revealed that odds ration for high risk group was 6.89 fold than low risk one (OR=6.82, CV95, 2.9-16.06).Two point serial correlation between DAS-26 and psychiatrist diagnosis was 0.44. Also, major depression and dysthymic disorder was significantly predicted by general health subscales (P<0.001).Conclusion: Dysfunctional attitude may be a predisposing risk factor of depression. Predict depression support and Beck's cognitive diathesis stress theory of depression that dysfunctional attitude (26 options) can be used for determination of depression in this group.