Incident-rate measures

This small plant size presented a problem for safety measurement in the company. In 1993 the company was well along with the implementation of a total quality management implementation. Based on the recent training in variation and the use of control charts, the safety managers had begun to use U charts when looking at incident-rate measures. The wide limits of variation encountered with small plant sizes convinced them that incident rates would not be particularly useful as a measure of performance in the company, at least for small sites and for short time periods. 

In addition, the results tend to establish the applicability of a behaviorally based, positive measure of safety. Such a measure is useful for measuring and enhancing the presence of safety while other, after-the-fact measures based on accident/incidence rates measure only the absence of safety. 

End-of-pipe measures continue to be vitally important. The largest PSM and ESH management costs are accident and incident related. If you reduce the costs of managing PSM and ESH, yet accident and incident rates rise beyond any normal statistical variation, the new system is costing the company more. Near misses are a leading indicator for accidents and incidents and should not be neglected. 

Janssen and Hoogland (J3, J4a) made an extensive study of mass transfer during gas evolution at vertical and horizontal electrodes. Hydrogen, oxygen, and chlorine evolution were visually recorded and mass-transfer rates measured. The mass-transfer rate and its dependence on the current density, that is, the gas evolution rate, were found to depend strongly on the nature of the gas evolved and the pH of the electrolytic solution, and only slightly on the position of the electrode. It was concluded that the rate of flow of solution in a thin layer near the electrode, much smaller than the bubble diameter, determines the mass-transfer rate. This flow is affected in turn by the incidence and frequency of bubble formation and detachment. However, in this study the mass-transfer rates could not be correlated with the square root of the free-bubble diameter as in the surface renewal theory proposed by Ibl (18). 

Another way of measuring accident performance is by the LTIR, or lost-time injury rate. This is identical to the OSHA incidence rate based on incidents in which the employee is unable to continue their normal duties. A plant site has 1200 full-time employees working 40 hr/week and 50 weeks/yr. If the plant had 2 lost-time incidents last year, what is the LTIR ... 

Measures of the public health importance of a disease include the absolute number of cases, the incidence rate, the prevalence (rate), the economic impact of the disease, and the prognosis and preventability of the disease.65 Contact dermatitis is the most common occupational and environmental skin disease. Epidemiologic data show that contact dermatitis comprises 90 to 95% of all occupational skin diseases. 

Any inferences about the difference between the effects of the two treatments that may be made upon such data are the observed rates, or proportions of deteriorations by the intrathecal route. In this example, amongst those treated by the intrathecal route 22/58 = 0.379 of patients deteriorated, and the corresponding control rate is 37/60 = 0.617. The observed rates are estimates of the population incidence rates, jtt for the test treatment and Jtc for the controls. Any representation of differences between the treatments will be based upon these population rates and the estimated measure of the treatment effect will be reported with an associated 95% confidence interval and/or p-value. 

However, this option presents some difficulties for radionuclides, because studies of radiation effects in human populations have focused on cancer fatalities as the measure of response and probability coefficients for radiation-induced cancer incidence have not yet been developed by ICRP or NCRP for use in radiation protection. Probabilities of cancer incidence in the Japanese atomic-bomb survivors have been obtained in recent studies (see Section 3.2.3.2), but probability coefficients for cancer incidence appropriate for use in radiation protection would need to take into account available data on cancer incidence rates from all causes in human populations of concern, which may not be as reliable as data on cancer fatalities. Thus, in effect, if incidence were used as the measure of stochastic response for radionuclides, the most technically defensible database on radiation effects in human populations available at the present time (the data on fatalities in the Japanese atomic-bomb survivors) would be given less weight in classifying waste. 

There is more than one method to calculate fatality rates that measure the incidence of fatal work injuries for groups of workers. An hours-based rate measures the risk of fatality per standardized length of exposure an employment-based rate measures the risk for those employed during a given period of time. 

The OXVASC study showed that the annual incidence of stroke in the UK in the first few years of this century, including subarachnoid hemorrhage, was 2.3/1000 and the incidence of TIA was 0.5/1000 (Rothwell et al. 2005), with about a quarter of events occurring in those under the age of 65 and about a half in those above the age of 75 (Fig. 1.1). The incidence of cerebrovascular events in OXVASC was similar to that of acute coronary vascular events in the same population during the same period (Fig. 1.2), with a similar age distribution (Rothwell et al 2005). Incidence rates, however, measure first-ever-in-a-lifetime definite events only and exclude possible, recurrent and suspected events, so do not represent the true burden of a condition. This is especially true for TIA, where a significant proportion of cases referred to a TIA service have alternative, non-vascular... 

Table 1.5. Incidence rates of transient ischemic attack and stroke according to stringency of definition applied and previous cerebrovascular disease measured in OXVASC (2002-2005)...

Once data are available, several types of analysis are possible. The most straightforward is comparison of disease incidence rate in different exposure groups (number of new cases/person-time). The case-referent approach is conceptually similar but will yield risk multipliers rather than direct measurements of incidence rate. Comparisons of prevalence may be problematic because of the survivorship issues discussed above. 

Cohort study (incidence rate) and nested case-control M (10,486) Gold miners (incident cases) High incidence (8.2 per 100 000 person years), but no difference in exposure measures between cases and controls Cowie (1987)... 

Dry Etch Resistance. Polyvinylnaphthalene and its derivatives were reported to be highly resistant to dry etching ( 9 ). Under Ar ion milling or CCl sputter etching conditions, etch rates for poly(2-vinylnaphthalene) were found to be about two-thirds of those for polystyrene or novolak resin resists. To find relationships between etch resistance and chemical structure, etch rate measurements for various metal-free polymers were made under Ar or C>2 ion beam incidence. It was found that the etch rate under ion bombardment depends linearly on N/(Nc -N0), where N denotes the total number of atoms in a monomer unit, Nc and N0 are the number of carbon atoms and the number of oxygen atoms in a monomer unit, respectively ( ). The dependence on "N/(NC-N0) factor" indicates that... 

Fontana, A., Picoco, C., Masala, G., Prastaro, C., and Vineis, R, Incidence rates of lymphomas and environmental measurements of phenoxy herbicides Ecological analysis and case-control study. Arch Environ Health, 53, 384-387, 1998. 

---