Occupational radiation exposure and mortality: second analysis of the National Registry for Radiation Workers
C R MuirheadAdrian GoodillRichard HaylockJ VokesMark P. LittleDavid A. JacksonJ A O'HaganJ.M. ThomasG M KendallT.J. SilkD. L. C. BinghamG. Berridge
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The National Registry for Radiation Workers (NRRW) is the largest epidemiological study of UK radiation workers. Following the first analysis published in 1992, a second analysis has been conducted using an enlarged cohort of 124 743 workers, updated dosimetry and personal data for some workers, and a longer follow-up. Overall levels of mortality were found to be less than those expected from national rates; the standardised mortality ratio for all causes was 82, increasing to 89 after adjusting for social class. This `healthy worker effect' was particularly strong for lung cancer and for some smoking-related non-malignant diseases. Analysis of potential radiation effects involved testing for any trend in mortality risk with external dose, after adjusting for likely confounding factors. For leukaemia, excluding chronic lymphatic leukaemia (CLL), the central estimate of excess relative risk (ERR) per Sv was similar to that estimated for the Japanese atomic bomb survivors at low doses (without the incorporation of a dose-rate correction factor); the corresponding 90% confidence limits for this trend were tighter than in the first analysis, ranging from just under four times the risk estimated at low doses from the Japanese atomic bomb survivors to about zero. For the grouping of all malignancies other than leukaemia, the central estimate of the trend in risk with dose was closer to zero than in the first analysis; also, the 90% confidence limits were tighter than before and included zero. Since results for lung cancer and non-malignant smoking-related diseases suggested the possibility of confounding by smoking, an examination was made, as in the first analysis, of all malignancies other than leukaemia and lung cancer. In this instance the central estimate of the ERR per Sv was similar to that from the A-bomb data (without the incorporation of a dose-rate correction factor), with a 90% confidence interval ranging from about four times the A-bomb value to less than zero. For multiple myeloma there was an indication of an increasing trend in risk with external dose (p = 0.06), although the evidence for this trend disappeared after omitting workers monitored for exposure to internal emitters. The second NRRW analysis provides stronger inferences than the first on occupational radiation exposure and cancer mortality; the 90% confidence intervals for the risk per unit dose are tighter than before, and now exclude values which are greater than four times those seen among the Japanese A-bomb survivors, although they are also generally consistent with an observation of no raised risk. Furthermore, there is evidence, of borderline statistical significance, of an increasing risk for leukaemia excluding CLL, and, as with solid cancers, the data are consistent with the A-bomb findings.Keywords:
Absolute risk reduction
Standardized mortality ratio
Abstract Background: Cutaneous basal cell carcinoma (BCC) has long been associated with UV radiation (UVR) exposure, but data are limited on risks by anatomic site. Methods: We followed 63,912 cancer-free White U.S. radiologic technologists from cohort entry (1983–1989/1994–1998) to exit (date first BCC via 2003–2005 questionnaire). We estimated associations between cumulative ambient UVR and relative/absolute risks of self-reported BCC by anatomic location via Poisson models. Results: For incident first primary BCC in 2,124 subjects (mean follow-up, 16.9 years) log[excess relative risks] (ERR) of BCC per unit cumulative ambient UVR = 1.27/MJ cm–2 [95% confidence interval (CI): 0.86–1.68; Ptrend < 0.001] did not vary by anatomic site (P = 0.153). However, excess absolute risks of BCC per unit cumulative ambient UVR were large for the head/neck = 5.46/MJ cm–2/104 person-year (95% CI: 2.92–7.36; Ptrend < 0.001), smaller for the trunk (2.56; 95% CI: 1.26–3.33; Ptrend = 0.003), with lesser increases elsewhere. There were lower relative risks, but higher absolute risks, for those with Gaelic ancestry (P < 0.001), also higher absolute risks among those with fair complexion, but relative and absolute risks were not generally modified by other constitutional, lifestyle or medical factors for any anatomic sites. Excess absolute and relative risk was concentrated 5–15 years before time of follow-up. Conclusions: BCC relative and absolute risk rose with increasing cumulative ambient UVR exposure, with absolute risk highest for the head/neck, to a lesser extent in the trunk. Impact: These associations should be evaluated in other White and other racial/ethnic populations along with assessment of possible modification by time outdoors, protective, and behavioral factors.
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For the presentation of risk, both relative and absolute measures can be used. The relative risk is most often used, especially in studies showing the effects of a treatment. Relative risks have the appealing feature of summarizing two numbers (the risk in one group and the risk in the other) into one. However, this feature also represents their major weakness, that the underlying absolute risks are concealed and readers tend to overestimate the effect when it is presented in relative terms. In many situations, the absolute risk gives a better representation of the actual situation and also from the patient's point of view absolute risks often give more relevant information. In this article, we explain the concepts of both relative and absolute risk measures. Using examples from nephrology literature we illustrate that unless ratio measures are reported with the underlying absolute risks, readers cannot judge the clinical relevance of the effect. We therefore recommend to report both the relative risk and the absolute risk with their 95% confidence intervals, as together they provide a complete picture of the effect and its implications.
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To understand the magnitude of risk of health events, such as cardiovascular diseases (CVD), related to poor oral health, both relative and absolute risk measures should be reported. Our aim was to investigate the extent to which absolute and relative measures of risk are reported in longitudinal studies that assess the association between oral health indicators (OHIs) and CVD.A systematic search of longitudinal studies investigating the association of any OHI with CVD was carried out using the Embase, Medline and Cochrane library databases. The search covered each database from its inception date to August 2021. Data about reporting relative and absolute risks of the relationship between CVD and OHI from the abstract were extracted. If the relative risk for OHIs and CVD was reported in the abstract, then the underlying absolute risks were searched from the full text, and it was assessed whether it was similarly adjusted for confounding than was the relative risk in the abstract.One hundred-six articles were included. From these, 85 (80%) studies reported the association of OHIs and CVD with one or more relative risks in the abstract. Of those 85 studies, the underlying absolute risks were accessible or calculable from the abstract or full text of 60 studies. However, of these 60 studies, in only 10 (12%), the underlying absolute risks were similarly adjusted, as were the relative risks in the abstract. The absolute risks of CVD by OHIs were rarely reported without corresponding relative risks in the abstract (n = 2, 2%). Median absolute risk difference in the CVD risk between exposure levels to which the first relative risk in the abstract referred was 1.8% (interquartile range 0.6-4.6, n = 63).Focusing on relative risks over absolute risks was a common practice in literature. Reporting similarly adjusted underlying absolute risks of relative risks was rare in most studies, despite those being helpful for comprehending the magnitude of CVD-risk increase related to poor oral health. Current reporting practices could lead to an overinterpretation of risk increase of CVD related to poor oral health.
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Background: Carotid revascularization was addressed by NASCET and ACAS. NASCET showed a 2-year stroke and death of 32.3% in medical patients and a 15.8% incidence in surgical patients (16.5% absolute/51% relative reduction). Similarly, ACAS revealed an 11% 5-year risk in medical patients and 5.1% in surgical patients (5.9% absolute reduction/53% relative reduction). Absolute risk (rather than relative risk) reduction is of prime interest to the patient. However, in these studies, treatment efficacy was assessed on a relative basis, and these procedures were equally efficacious (51% vs. 53% relative risk). The higher event rates in the symptomatic patients resulted in a larger absolute risk reduction in NASCET (16.5% vs. 5.9%). CREST is the only carotid revascularization study to include both symptomatic and asymptomatic patients undergoing CEA or carotid artery stenting (CAS), and we looked at absolute and relative risks associated with both procedures. Methods: Treatment differences in CREST by symptomatic status were reviewed and interaction terms analyzed. Results: Symptomatic periprocedural stroke and death rates were 6% for CAS vs. 3.2% for CEA (2.8% absolute/47% relative difference/p = 0.02), and were 2.5% for CAS vs. 1.4% for CEA (1.2% absolute/53% relative difference/p = 0.15) for asymptomatic. While treatment differences in periprocedural rates were significant for symptomatic but not asymptomatic patients, there was no difference in treatment efficacy as determined by relative risk reduction. Even the most prominent interaction terms were clearly not significant, p > 0.38. Discussion: There is no evidence of a CAS-CEA difference in treatment efficacy by symptomatic status in CREST. There are significant findings in symptomatic patients. This is likely a product of an increased background rate of events in this strata. While symptomatic status can identify a subgroup with an increased background rate, other factors (e.g. age or stenosis) could identify subgroups of asymptomatic patients with high event rates and large absolute treatment differences.
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BACKGROUND Relative risks are the most common statistics used to quantify the risk of mortal or morbid outcomes associated with different patient groups and therapeutic interventions. However, absolute risks are of greater value to both patient and physician in making clinical decisions. METHODS The relationship between relative and absolute risks is explained using graphical aids. A program to estimate absolute risks from relative risks is available on the Internet (see ftp://ftp.vanderbilt.edu/pub/biostat/absrisk.txt). This program uses a competing hazards model of morbidity and mortality to derive these estimates. RESULTS When a patient's absolute risk is low, it can be approximated by multiplying her relative risk by the absolute risk in the reference population. This approximation fails for higher absolute risks. The relationship between relative and absolute risk can vary dramatically for different diseases. This is illustrated by breast cancer morbidity and cardiovascular mortality in American women. The accuracy of absolute risk estimates will be affected by the accuracy of relative risk estimates, by the appropriateness of the reference groups used to calculate relative risks, by the stability of cross-sectional, age-specific morbidity and mortality rates over time, by the influence of individual risk factors on multiple causes of mortality, and by the extent to which relative risks may vary over time. CONCLUSIONS Valid absolute risk estimates are valuable when making treatment decisions. They can often be obtained over time intervals of 10 to 20 years when the corresponding relative risk estimates have been accurately determined. Cancer 1996;77:2193-9.
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Abstract Physicians expect a treatment to be more effective when its clinical outcomes are described as relative rather than as absolute risk reductions. We examined whether effects of presentation method (relative vs. absolute risk reduction) remain when physicians are provided the baseline risk information, a vital piece of statistical information omitted in previous studies. Using a between-subjects design, ninety five physicians were presented the risk reduction associated with a fictitious treatment for hypertension either as an absolute risk reduction or as a relative risk reduction, with or without including baseline risk information. Physicians reported that the treatment would be more effective and that they would be more willing to prescribe it when its risk reduction was presented to them in relative rather than in absolute terms. The relative risk reduction was perceived as more effective than absolute risk reduction even when the baseline risk information was explicitly reported. We recommend that information about absolute risk reduction be made available to physicians in the reporting of clinical outcomes. Moreover, health professionals should be cognizant of the potential biasing effects of risk information presented in relative risk terms.
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BACKGROUND Relative risks are the most common statistics used to quantify the risk of mortal or morbid outcomes associated with different patient groups and therapeutic interventions. However, absolute risks are of greater value to both patient and physician in making clinical decisions. METHODS The relationship between relative and absolute risks is explained using graphical aids. A program to estimate absolute risks from relative risks is available on the Internet (see ftp://ftp.vanderbilt.edu/pub/biostat/absrisk.txt). This program uses a competing hazards model of morbidity and mortality to derive these estimates. RESULTS When a patient's absolute risk is low, it can be approximated by multiplying her relative risk by the absolute risk in the reference population. This approximation fails for higher absolute risks. The relationship between relative and absolute risk can vary dramatically for different diseases. This is illustrated by breast cancer morbidity and cardiovascular mortality in American women. The accuracy of absolute risk estimates will be affected by the accuracy of relative risk estimates, by the appropriateness of the reference groups used to calculate relative risks, by the stability of cross-sectional, age-specific morbidity and mortality rates over time, by the influence of individual risk factors on multiple causes of mortality, and by the extent to which relative risks may vary over time. CONCLUSIONS Valid absolute risk estimates are valuable when making treatment decisions. They can often be obtained over time intervals of 10 to 20 years when the corresponding relative risk estimates have been accurately determined. Cancer 1996;77:2193-9.
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Background
Treatment acceptance by patients is influenced by the way treatment effects are presented. Presentation of benefits using relative risk increases treatment acceptance compared to the use of absolute risk. It is not known whether this effect is modified by prior presentation of a patient9s individualised risk estimate or how presentation of treatment harms by relative or absolute risk affects acceptance.Aim
To compare acceptance of a hypothetical treatment to prevent hip fracture after presentation of the treatment9s benefit in relative or absolute terms in the context of a personal fracture risk estimate, and to reassess acceptance following subsequent presentation of harm in relative orabsolute terms.Design and setting
Randomised controlled trial of patients recruited from 10 GPs9 lists in Christchurch, New Zealand.Method
Women aged ≥50 years were invited to participate. Participants were given a personal 10-year hip fracture risk estimate and randomised to receive information on a hypothetical treatment9s benefit and harm in relative orabsolute terms.Results
Of the 1140 women invited to participate 393 (34%) took part. Treatment acceptance was greater following presentation of benefit using absolute terms than relative terms after adjustment forage, education, previous osteoporosis diagnosis, and self-reported risk (OR 1.73, 95% confidence interval [CI] = 1.10 to 2.73, P = 0.018). Presentation of the treatment9s harmful effect in relative terms led to a greater proportion of participants declining treatment than did presentation in absolute terms (OR 4.89, 95% CI = 2.3 to 11.0, P<0.001).Conclusion
Presentation of treatment benefit and harm using absolute risk estimates led to greater treatment acceptance than presentation of the same information in relative terms.Absolute risk reduction
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The effects of an intervention is best measured in a randomized controlled trial (RCT) and can be expressed in various ways using the measures such as risk difference, number needed to treat (NNT), relative risk or odds ratio. Risk difference (RD) is the difference in risk of the outcome event between control and experimental group. Control group is not exposed to the intervention, whereas experimental group is the one that is exposed to intervention. The risk of outcome event in the control group is also called baseline risk. The NNT is the inverse of the risk difference and indicates the number of patients required to be treated to avoid one additional outcome event. Risk difference and NNT are absolute measures of effect. Relative risk (RR) is a relative measure and is the ratio of the risk in the exposed group to that in the unexposed group. Relative risk reduction (RRR) is one minus RR and indicates the fraction (or percent) of baseline risk that reduces with exposure to the intervention. Odds ratio (OR) is ratio of odds of having the event in the exposed group to that in the unexposed group. These measures are suitable for different purposes and appeal to different constituencies. Odds ratio is the only measure suitable for use in logistic regression and case control studies.
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