Odds ratio OR

In order to understand the odds ratio you first of all need to understand odds. For the data of Example 3.3 consider each of the treatment groups separately. 

For the trastuzumab group, the odds of a patient suffering SAEs are 117/1560 = 0.075 for every patient free from SAEs there are 0.075 patients suffering SAEs. For the observation only group the odds of a patient suffering SAEs are 81/1629 = 0.050. In this group for every patient not suffering SAEs there are 0.050 patients who do suffer SAEs. 

The odds ratio (OR) is then the ratio of the odds of a patient suffering one or more SAEs  

Usually, the odds relating to the test treatment group go on the top when calculating the ratio (the numerator), while the odds for the control group go on the bottom (the denominator). However there is no real convention regarding whether it is the odds in favour of success or the odds in favour of failure that we calculate. Had we chosen to calculate the odds in favour of no SAE, the odds ratio would have been which has the value 0.66(= 1/1.51) so take care that when you see an odds ratio presented you are clear how the calculation has been organised. 

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Odds Ratio (OR)—A means of measuring the association between an exposure (such as toxic substances and a disease or condition) which represents the best estimate of relative risk (risk as a ratio of the incidence among subjects exposed to a particular risk factor divided by the incidence among subjects who were not exposed to the risk factor). An odds ratio of greater than 1 is considered to indicate greater risk of disease in the exposed group compared to the unexposed. 

In a case-control study of the relation between occupational exposures to various suspected estrogenic chemicals and the occurrence of breast cancer, the breast cancer odds ratio (OR) was not elevated above unity (OR=0.8 95% 01=0.2-3.2) for occupational exposure to endosulfan compared to unexposed controls (Aschengrau et al. 1998) however, the sample sizes were very small (three exposed seven not exposed), and co-exposure to other unreported chemicals also reportedly occurred. Both of these factors may have contributed to the high degree of uncertainty in the OR indicated by the wide confidence interval. 

One meta-analysis examined the safety and efficacy of LMWH and heparinoids in 11 randomized trials of 3048 patients with acute ischemic stroke. It reported a reduction in the incidence of deep venous thrombosis (DVT) (odds ratio (OR) 0.27,... 

Growing experience with complex disease genetics has made clear the need to minimize type I error in genetic studies [41, 109]. Power is especially an issue for SNP-based association studies of susceptibility loci for phenomenon such as response to pharmacological therapy, which are extremely heterogeneous and which are likely to involve genes of small individual effect. Table 10.2 shows some simple estimation of required sample sizes of cases needed to detect a true odds ratio (OR) of 1.5 with 80% power and type I error probability (a) of either 0.05 or 0.005. 

Typically statisticians use one of the three approaches to represent treatment differences for such data absolute rate reduction (ARR), relative risk (RR) and the odds ratio (OR). 

If this confidence interval is on the log scale, for example with both the odds ratio and the hazard ratio, then both the lower and upper confidence limits should be converted by using the anti-log to give a confidence interval on the original odds ratio or hazard ratio scale. 

Pooled 95 per cent confidence interval well away from zero (or unity for odds ratios, or the pre-defined margin for non-inferiority trials)... 

Selected characteristics were compared between cases and controls by using test. The analyses of data were performed using the computer software SPSS for Windows version 11.5. Max type 1 error was accept as 0.05. Binary logistic regression was performed to calculate the odds ratios (ORs), and 95% confidence intervals (Cls) to assess the risk of breast cancer. 

A recent British trial, UK MRC ALL 97, randomized 1498 children to receive either 6-TG or 6-MP (87). After a median follow-up of 6 years, no differences in event-free survival were detected between the two treatment arms. A large reduction of isolated disease recurrence in the CNS by 6-TG [odds ratio (OR) = 0.53,95% confidence interval... 

A nested case-control study within a cohort of rubber workers in the United States was performed to examine the relationship between exposure to solvents and the risk of cancer (Checkoway et al., 1984 Wilcosky et al., 1984). The cohort consisted of 6678 male rubber workers who either were active or retired between 1964 and 1973. The cases comprised all persons with fatal stomach cancer (n = 30), respiratory system cancer (z7 = 101), prostate cancer ( = 33), lymphosarcoma (n = 9) or lymphocytic leukaemia (z7 = 10). These sites were chosen because they were those at which cancers had been found to be in excess in an earlier cohort analysis (McMichael et al., 1976). The controls were a 20% age-stratified random sample of the cohort (z = 1350). Exposure was classified from a detailed work history and production records. An association was observed between exposure for one year or more to carbon tetrachloride and lymphocytic leukaemia (odds ratio (OR), 15.3 / < 0.0001, based on eight exposed cases) and lymphosarcoma (OR, 4.2 p < 0.05, based on six exposed cases) after adjusting for year of birth. The relative risk associated with 24 solvents was examined and levels of exposure were not reported. [The Working Group noted that overlapping exposures limit the ability to draw conclusions regarding carbon tetrachloride.]... 

In a case-control study within a cohort of 6678 rubber workers in the United States (lARC, 1987) (Wilcosky et al., 1984), one of the substances assessed was xylene, which was analysed as a potential risk factor in relation to each of five cancer types. There were somewhat increased odds ratios (OR) for prostate cancer (OR, 1.5 n = 8), lymphosarcoma (OR, 3.7 n = 4 p < 0.05) and lymphatic leukaemia (OR, 3.3 n = 4). [The Working Group noted that workers were typically exposed to multiple exposures.]... 

Table 20.2 Odds Ratios (OR) and 95% Confidence Intervals (Cl) Among 304 Cases of Squamous Cell Cancer of the Esophagus and 743 Controls, According to Daily Intake Quintile of Five Classes of Flavonoids and Total Flavonoids. Italy, 1992-1997.

In 1995, a study by the National Transportation Safety Board on fatal accidents in professional trucks drivers (27) showed that the mean duration of sleep among drivers was below 6 hr of sleep in the last 24 hr before the accident. Connor et al. (8) showed that sleepiness at the wheel increased the risk of causing a traffic accident by 8.2-fold. Sleeping less than 5 hr in the 24 hr before the accident and driving between 2 and 5 a.m. were also significant risk factors for accidents [odds ratio (OR) = 2.7 and OR = 5.6, respectively],... 

A number of studies have examined pregnancy outcomes following paternal exposure or paternal and maternal exposure to 2,3,7,8-TCDD. No significant alterations in the incidence of spontaneous abortions were found in several studies of Vietnam veterans. In a case-control study conducted by Aschengrau and Monson (1989), no association was observed between paternal military service in Vietnam and the risk of spontaneous abortion (odds ratio [OR] of 0.88, 95% confidence interval [Cl] of 0.42-1.86). A limitation of this study is that service in Vietnam is not an adequate exposure surrogate for 2,3,7,8-TCDD exposure ... 

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