Correlation metric

The logit model is a widely used regression technique in social research. However, the use and interpretation of coefficients from logit models have proven contentious. Problems arise because the mean and the variance of discrete variables cannot be separated. Logit coefficients are identified relative to an arbitrary scale, which makes the coefficients difficult both to interpret and to compare across groups or samples. Do differences in coefficients reflect true differences or differences in scales? This cross-sample comparison problem raises concerns for comparative research. However, we suggest a new correlation metric, derived from logit models, which gives new interpretation to the estimates of logit models (log odds-ratios). The metric leads the way to a reorientation of the use of logit models, because it helps to clarify what logit coefficients are and how and when logit coefficients can (or cannot) be used in comparative research. The metric recovers the correlation between a predictor variable x and a continuous latent outcome variable y* assumed to underlie a binary observed outcome y. This metric is truly invariant to differences in the marginal distributions of x and y* across groups or samples, making it suitable for situations met in real applications in comparative research. Our derivations also extend to the probit and to ordered and multinomial models. The new metric is implemented in the Stata command nlcorr.

Zeno effect preventing Rabi transitions onto an unstable energy level

We consider a driven 2-level system with one level showing spontaneous decay to an otherwise uncoupled third level. Rabi transitions to the unstable level are strongly damped. This simple configuration can be used to demonstrate and to explore the quantum Zeno effect leading to a freezing of the system to the initial level. A comparison with repeated projection measurements is given. A treatment within a phenomenological theory of continuous measurements is sketched. The system visualizes the important role of null measurements (negative result measurements) and may serve as a good example for a truly continuous measurement.Comment: 13 pages, Latex, 2 EPS figure

Uptake and efflux of 64Cu by the marine cyanobacterium Synechococcus (WH7803)

The uptake and efflux of 64Cu was studied in the marine cyanobacterium Synechoccous strain WH7803 (DC2). Uptake followed classical Michaelis-Menten type kinetics in metal-buffered seawater. The maximum uptake rate, Vmax, was 0.236 ± 0.016 × 10-18 mol Cu cell-1 h-1, with the half-saturation constant, KS, of 10-10.81±0.11 mol L-1. An efflux mechanism was also observed in WH7803, whose growth was inhibited by high internal Cu concentrations. Efflux of Cu enabled WH7803 to maintain homeostasis for Cu at typical seawater ambient free copper concentrations ([Cu2+]f). The sensitivity of WH7803 growth to Cu was related to a simple inability to regulate internal Cu concentrations when external concentrations were >10-11 mol L-1

Allochthonous matter : an important factor shaping the phytoplankton community in the Baltic Sea

It is well-known that nutrients shape phytoplankton communities in marine systems, but in coastal waters allochthonous dissolved organic matter (ADOM) may also be of central importance. We studied how humic substances (proxy of ADOM) and other variables influenced the nutritional strategies, size structure and pigment content of the phytoplankton community along a south-north gradient in the Baltic Sea. During the summer, the proportion of mixotrophs increased gradually from the phosphorus-rich south to the ADOM-rich north, probably due to ADOM-fueled microbes. The opposite trend was observed for autotrophs. The chlorophyll a (Chl a): carbon (C) ratio increased while the levels of photoprotective pigments decreased from south to north, indicating adaptation to the darker humic-rich water in the north. Picocyanobacteria dominated in phosphorusrich areas while nanoplankton increased in ADOM- rich areas. During the winter-spring the phytoplankton biomass and concentrations of photoprotective pigments were low, and no trends with respect to autotrophs and mixotrophs were observed. Microplankton was the dominant size group in the entire study area. We conclude that changes in the size structure of the phytoplankton community, the Chl a: C ratio and the concentrations of photoprotective pigments are indicative of changes in ADOM, a factor of particular importance in a changing climate.Peer reviewe

Protein, iron, and meat consumption and risk for rheumatoid arthritis: a prospective cohort study

A recent prospective study showed that higher consumption of red meat and total protein was associated with increased risk for inflammatory polyarthritis. We therefore prospectively examined the relationship between diet (in particular, protein, iron, and corresponding food sources) and incident rheumatoid arthritis (RA) among 82,063 women in the Nurses' Health Study. From 1980 to 2002, 546 incident cases of RA were confirmed by a connective tissue disease screening questionnaire and medical record review for American College of Rheumatology criteria for RA. Diet was assessed at baseline in 1980 and five additional times during follow up. We conducted Cox proportional hazards analyses to calculate the rate ratio of RA associated with intakes of protein (total, animal, and vegetable) and iron (total, dietary, from supplements, and heme iron) and their primary food sources, adjusting for age, smoking, body mass index, and reproductive factors. The multivariate models revealed no association between RA and any measure of protein or iron intake. In comparisons of highest with lowest quintiles of intake, the rate ratio for total protein was 1.17 (95% confidence interval 0.89–1.54; P for trend = 0.11) and for total iron it was 1.04 (95% confidence interval 0.77–1.41; P for trend = 0.82). Red meat, poultry, and fish were also not associated with RA risk. We were unable to confirm that there is an association between protein or meat and risk for RA in this large female cohort. Iron was also not associated with RA in this cohort

Genetic Risk Score Predicting Risk of Rheumatoid Arthritis Phenotypes and Age of Symptom Onset

Cumulative genetic profiles can help identify individuals at high-risk for developing RA. We examined the impact of 39 validated genetic risk alleles on the risk of RA phenotypes characterized by serologic and erosive status.We evaluated single nucleotide polymorphisms at 31 validated RA risk loci and 8 Human Leukocyte Antigen alleles among 542 Caucasian RA cases and 551 Caucasian controls from Nurses' Health Study and Nurses' Health Study II. We created a weighted genetic risk score (GRS) and evaluated it as 7 ordinal groups using logistic regression (adjusting for age and smoking) to assess the relationship between GRS group and odds of developing seronegative (RF- and CCP-), seropositive (RF+ or CCP+), erosive, and seropositive, erosive RA phenotypes. In separate case only analyses, we assessed the relationships between GRS and age of symptom onset. In 542 RA cases, 317 (58%) were seropositive, 163 (30%) had erosions and 105 (19%) were seropositive with erosions. Comparing the highest GRS risk group to the median group, we found an OR of 1.2 (95% CI = 0.8-2.1) for seronegative RA, 3.0 (95% CI = 1.9-4.7) for seropositive RA, 3.2 (95% CI = 1.8-5.6) for erosive RA, and 7.6 (95% CI = 3.6-16.3) for seropositive, erosive RA. No significant relationship was seen between GRS and age of onset.Results suggest that seronegative and seropositive/erosive RA have different genetic architecture and support the importance of considering RA phenotypes in RA genetic studies

Achievement of combined goals of low-density lipoprotein cholesterol and non-high-density lipoprotein cholesterol with three different statins: results from VOYAGER

Background: Guidelines suggest that the combination of low-density lipoprotein cholesterol (LDL-C) and non-high-density lipoprotein cholesterol (non-HDL-C) is the most clinically relevant goal for lipid-lowering treatments. Methods: Data from VOYAGER, an individual patient data meta-analysis including 32,258 patients from 37 clinical trials, was used to determine the percentage of patients reaching combined goals of LDL-C and non-HDL-C following treatment with simvastatin, atorvastatin, or rosuvastatin. Paired comparisons were made between each dose of rosuvastatin and the same or higher doses of simvastatin and atorvastatin. Results: Each dose of rosuvastatin brought significantly more patients to the combined goal of LDL-C < 100 mg/dL and non-HDL-C < 130 mg/dL than the same or double dose of atorvastatin; atorvastatin 80 mg was significantly superior to rosuvastatin 10 mg (all p < 0.001). Each dose of rosuvastatin helped significantly more patients reach the combined goal than any dose of simvastatin (all p < 0.001), except for rosuvastatin 10 mg versus simvastatin 80 mg (non-significant). Also, each dose of rosuvastatin helped significantly more patients to reach the combined goal of LDL-C < 70 mg/dL and non-HDL-C < 100 mg/dL than the same or double dose of atorvastatin (all p < 0.001). Every dose of rosuvastatin was significantly superior to all doses of simvastatin (all p ≤ 0.020), except for rosuvastatin 10 mg versus simvastatin 40 mg and 80 mg (non-significant). Conclusions: Physicians' choice of statin and dose is important in helping patients achieve the combined LDL-C and non-HDL-C goals recommended in established guidelines.Björn W. Karlson, Peter P. Toth, Michael K. Palmer, Philip J. Barter, Stephen J. Nicholl