Statistics relative risk

Car occupant Motorcyclists Mopeds (when distinction is made in statistics) Relative risk of motorcyclists vs. oar occupants... 

Return now to a point made early in this section. Statistical associations, the existence of which cohort and case-control studies can reveal to us, are not, of themselves, evidence of causation. If found, and even if they are strong - large relative risk or odds-ratio - they do not establish that the phenomena being investigated, the phenomena that are associated (disease and some exposure or other factor) are causally related. To see most easily why this is so, it is best to examine the difficulties that need to be overcome to move from association to any conclusion about the existence of a causal link. 

Recent publications on major clinical trials whose implications will involve a recommendation to change clinical practice have included summary statistics that quantify the risk of benefit or harm that may occur if the results of a given trial are strictly applied to an individual patient or to a representative cohort. Four simple calculations will enable the non-statistician to answer the simple question How much better would my chances be (in terms of a particular outcome) if I took this new medicine, than if I did not take it . These calculations are the relative risk reduction, the absolute risk reduction, the number needed to treat, and the odds ratio (see Box 6.3). 

At the level of individual hits, the database can be queried to retrieve either marketed BioPrint drugs that have that same activity, or the ADR associations discussed in the previous section can be queried to identify potential ADRs and their relative risks. At the profile level, compounds with similar profiles can be identified using standard statistical methods such as similarity metrics and hierarchical clustering. This similarity can be assessed using the whole panel of assays or by using selected subsets of those assays as determined by the user. Once compounds with similar profiles have been identified, in vivo data for the similar compoimds can be accessed and examined for information that may permit the user to anticipate in vivo effects. 

Chapter 3 together with testing hypotheses and the (dreaded ) p-value. Common statistical tests for various data types are developed in Chapter 4 which also covers different ways of measuring treatment effect for binary data, such as the odds ratio and relative risk. 

Finally, the statistical methods used to obtain estimates of relative risk, absolute rates of cancer, confidence intervals and significance tests, and to adjust for confounding should have been clearly stated by the authors. The methods used should preferably have been the generally accepted techniques that have been refined since the mid-1970s. These methods have been reviewed for case-control studies (Breslow Day, 1980) and for cohort studies (Breslow Day, 1987). 

Sensitivity, specificity, odds ratio, and relative risk Types of data and scales of measurement Measures of central tendency and dispersion Inferential statistics Students s t-distribution Comparing means Comparing more than two means Regression and correlation Nonparametric tests The x2-test Clinical trials INTRODUCTION... 

Intranasal calcitonin is associated with fewer adverse effects than parenteral formulations, probably because of low systemic availability. However, a meta-analysis has confirmed that adverse events are poorly reported in clinical trials (21). The pooled relative risk for rhinitis from four trials (n = 1663) was 1.72, but this did not reach statistical significance. 

A large number of epidemiology and case-control studies have examined the potential association between oral aluminum exposure and Alzheimer s disease. A number of these studies have been criticized for flawed patient selection, poor comparability of exposed and control groups, poor exposure assessment, poor assessment of health outcomes, and weak statistical correlations (Nieboer et al. 1995 Schupf et al. 1989). Studies conducted by Martyn et al. (1989), McLachlan et al. (1996), and Michel et al. (1990) have found an association between oral exposure to aluminum and an increased risk of Alzheimer s disease. In a survey study conducted by Martyn et al. (1989), the incidence of Alzheimer s disease in individuals under the age of 70 was estimated from computerized tomographic (CT) records. The 1,203 subjects lived in 88 county districts within England and Wales. Data on aluminum concentrations in the municipal water over a 10-year period were obtained from water authorities and water companies. The subjects were classified as having probable Alzheimer s disease, possible Alzheimer s disease, other causes of dementia, or epilepsy. The relative risks of Alzheimer s disease were elevated in the subjects living in districts with aluminum water concentrations of >0.01 mg/L. However, the relative risk exceeded unity only in the subjects with aluminum water concentrations of >0.11 mg/L (relative risk of 1.5, 95% confidence interval of 1.1-2.2). 

Several direct thrombin inhibitors have been studied in NSTEMI and STEM I patients and were compared to unfractionated heparin. In the GUSTO lib- and OASIS-2 trial (42,43), hirudin was studied versus heparin in patients with ACS. Despite early benefits, no statistical significance could be demonstrated at 30 days. Together with the OASIS-1 data, a combined analysis indicated a 22% relative risk reduction in cardiovascular death or Ml at 72 hours, 17% at 7 days, and 10% at 35 days (42). 

---