Bias in diet assessment methods--consequences of collinearity and measurement errors on power and observed relative risks

BACKGROUND: If several risk factors for disease are considered in a regression model and these factors are affected by measurement errors, the observed relative risk will be attenuated. In nutritional epidemiology, several nutrient variables show strong correlation, described as collinearity. The observed relative risk will then depend not only on the validity of the chosen diet assessment method but also on collinearity between variables in the model. METHODS: The validity of different diet assessment methods are compared. The correlation coefficients between common nutrients and foods are given using data from the Malm? Food Study. Intake of nutrients and foods were assessed with a modified diet history method, combining a 2-week food record for beverages and lunch/dinner meals and a food frequency questionnaire for other foods. The study population comprised 165 men and women aged 50-65 years. A multivariate logistic regression model is used to illustrate the effect of collinearity on observed relative risk (RRo). RESULTS: A moderate to high correlation between risk factors will substantially influence RRo even when using diet assessment methods with high validity. Methods with low validity might even give inverse RRo. CONCLUSION: It is stressed that caution must be exercised and only a selected number of variables should be included in the model, especially when they are highly intercorrelated, since RRo might be severely biased.     

Changing Frames of Mobility through Radical Policy Interventions? The Stockholm Congestion Tax

The introduction of a congestion tax was a significant moment in the management of mobility in Stockholm. This paper critically examines this apparent consensus on confronting car based mobility, by analysing how mobility was framed at key stages in policy making, from the 1970s through to the trial in 2006 and subsequent implementation. Changing transport objectives are compared, and winners and losers are traced in relation to motility and environmental quality. The paper argues that a car-based automobility frame survives, even in the implementation of a radical policy of congestion taxation.     

Embrittlement of a continuously cooled Fe-25 Cr alloy

A study has been carried out on the effects of isothermal heat treatment at 475 and 550‡C and of continuous cooling at different rates from 850°C on the brittleness (as assessed by the ductile-brittle impact transition temperature) of a vacuum melted Fe-25 Cr alloy. The ductile-brittle transition temperature was found to be the lowest for the water quenched condition and highest for the furnace cooled condition and for material aged at 475‡C for long times (~500 h). An increase of brittleness with decreased cooling rate in the continuously cooled samples is attributed to the formation of more continuous and larger amounts of chromium nitrides and carbonitrides at the grain boundaries. Very little or no body centered cubic chromium-rich phase (alpha prime), associated with 475°C embrittlement, was observed. On aging at 550°C, the increased brittleness with time is also accounted for by the formation of grain boundary nitrides and carbonitrides. Although a similar effect takes place in the alloy heat treated at 475°C, the precipitation of alpha prime after long aging times enhances the brittleness. The tendency towards a more brittle condition with aging treatment and slower cooling rate is explained in terms of the Cottrell theory for brittle fracture.     

Analytical inversion formula for uniformly attenuated fan-beamprojections

A convolution backprojection algorithm was derived by Tretiak and Metz (198) to reconstruct two-dimensional (2-D) transaxial slices from uniformly attenuated parallel-beam projections. Using transformation of coordinates, this algorithm can be modified to obtain a formulation useful to reconstruct uniformly attenuated fan-beam projections. Unlike that for parallel-beam projections, this formulation does not produce a filtered backprojection reconstruction algorithm but instead has a formulation that is an inverse integral operator with a spatially varying kernel. This algorithm thus requires more computation time than does the filtered backprojection reconstruction algorithm for the uniformly attenuated parallel-beam case. However, the fan-beam reconstructions demonstrate the same image quality as that of parallel-beam reconstructions     

Socioeconomic differences in 'avoidable' mortality in Sweden 1986-1990

BACKGROUND: 'Avoidable' mortality is commonly studied as an indicator of the outcome of health care. In this study socioeconomic differences in avoidable mortality in Sweden from 1986 to 1990 are analysed and related methodological issues discussed. METHODS: The 1985 Swedish Population and Housing Census was linked to the National Cause of Death Register 1986-1990. Mortality from potentially 'avoidable' causes of death was analysed for the age group 21-64 years. Analyses were performed for different socioeconomic groups, blue-collar workers, white-collar workers and the self-employed as well as for individuals outside the labour market. Standardized Mortality Ratios were calculated using standardization by age and sex. RESULTS: For all indicators studied, the death rates for those not in work were higher than for people at work. The largest differences were found for chronic bronchitis, diabetes, bacterial meningitis, ulcer of the stomach and duodenum, chronic rheumatic heart disease, asthma and hypertensive and cerebrovascular disease. For these causes of death the risk of dying was between 3.1 and 7.5 times greater in the non-working population than in the work-force. The differences in avoidable mortality between blue-collar workers and white-collar workers and the self-employed were, however, much smaller. For most of the indicators no significant differences were found. For ulcers of the stomach and duodenum, however the death rate for blue-collar workers was 2.8 times higher than those for other categories in work. CONCLUSIONS: The small difference in mortality outcome for different socioeconomic groups within the work-force indicates an equal quality of care for these groups. The greatly increased risk among the non-working population, however, is a warning sign. These results may be due to a 'healthy worker' effect. The measurement of socioeconomic differences in mortality may be dependent on the time-period chosen between occupational exposure and mortality outcome.     

An iterative reconstruction algorithm for single photon emission computed tomography with cone beam geometry

An iterative EM reconstruction algorithm for single photon emission computed tomography is implemented for cone beam geometry that uses a ray-driven projector-backprojector. The cone beam projector-backprojector models the attenuated Radon transform of a source distributed within an attenuator as line integrals of discrete voxels representing the source and attenuation distributions. The attenuation coefficient distribution for each voxel is assumed to be equal to the average value over a cubical region, and the integral of the source concentration through each voxel is obtained by interpolating between the source values at eight neighboring voxels. The calculation of the attenuation factors requires a specification of the attenuation distribution, estimated either from an assumed constant distribution with an estimated body outline or from transmission measurements. The distribution of attenuation coefficients is stored in memory, and the attenuation factors are calculated for each voxel during the projection and backprojection operations instead of using precalculated values. Computer simulations of half-scan and full-scan reconstructions show that the algorithm is able to compensate for attentuation and to suppress the propagation of artifacts that can result with limited angular sampling. The simulations verify that the algorithm has important application to cardiac SPECT imaging; because of variable attentuation through the thorax, it is necessary to use an iterative algorithm with an attenuation map in order to quantify radiopharmaceutical distributions in the heart.     

Microsatellites in the sand lizard (Lacerta agilis): description, variation, inheritance, and applicability

We developed microsatellite markers for the sand lizard (Lacerta agilis) to enable investigations of the genetic variability within and among populations with a heterogeneous spatial distribution in Sweden. The populations, which could not be characterized by variation in allozymes or mitochondrial DNA, had a substantial level of variability in microsatellite loci. However, the variability in Swedish populations was limited compared to a large, outbred Hungarian population. In the sand lizard, the number of (GT/CA)n repeats was approximately three times higher than that for (CT/GA)n. The number of repeats and the frequency of microsatellites were within the range reported for other species. Three of nine microsatellite loci showed alleles that could not be amplified, which is in agreement with recent reports describing microsatellite "null alleles" as a common occurrence. We discuss the caution which this calls for when calculating paternity probabilities and when estimating between-population allelic differentiation. A potential problem with different mutation rates for alleles within the same locus is discussed.     

Avoidable mortality among psychiatric patients

Avoidable mortality is a selection of causes of death considered to be amenable to health care and thereby used as an indicator of the quality of health care. In this study avoidable mortality for more than 30,000 psychiatric patients discharged from any hospital of Stockholm County between 1981 and 1985 has been followed up in the Cause of Death Register for the period 1986-1990. Standardised rate ratios were calculated for different groups of psychiatric disorders compared to the general population of Stockholm County for indicators of avoidable mortality, suicide, other mortality ("unavoidable") and causes possibly related to treatment with psychotrophic drugs. As expected, the psychiatric patients had the most pronounced elevated risk for suicide. i.e. 6- to 24-fold compared to the general population, and noticeably more elevated for women. It is also noteworthy that the relative mortality risks for diagnoses amenable to medical interventions and potential side-effects of psychotrophic drugs are higher than for other causes of death ("unavoidable"). The relative risks for avoidable mortality were 4.7 for men and 3.8 for women and for diagnoses possibly related to side-effects of psychotrophic drugs, 7.2. The relative risks for "unavoidable" mortality were 3.4 for men and 3.2 for women. The excess avoidable mortality rates for psychiatric patients and the elevated suicide risk, especially for female patients, are warning signals of shortcomings in psychiatric care that warrants further investigation.     

在硝酸介质中应用材料的选择

<正>在持久对抗腐蚀的过程中化工厂不仅需要考虑已知的腐蚀因素,还必须做好对抗潜在威胁因素的准备。对于工厂而言,最大的损害莫过于设备提前失效。如果这是因腐蚀引起的,则后果尤其严重。当然,材料的选择对任何一家工厂的效益都至关重要,需要充分考虑材料应用的环境因素。目前,大部分硝酸产品应用于化肥生产,工业用硝酸浓度一般为60%~65%。生产过程中所涉及的设备几乎都采用不锈钢(最常用的牌号为ASTM 304L,即山特维克公