Effects of exposure misclassification on regression analyses of epidemiologic follow-up study data

In epidemiologic studies, subjects are often misclassified as to their level of exposure. Ignoring this misclassification error in the analysis introduces bias in the estimates of certain parameters and invalidates many hypothesis tests. For situations in which there is misclassification of exposure in a follow-up study with categorical data, we have developed a model that permits consideration of any number of exposure categories and any number of multiple-category covariates. When used with logistic and Poisson regression procedures, this model helps assess the potential for bias when misclassification is ignored. When reliable ancillary information is available, the model can be used to correct for misclassification bias in the estimates produced by these regression procedures.     

An experimental facility for free air humidity manipulation (FAHM) can alter water flux through deciduous tree canopy

A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14 × 14 m experimental plots in the form of mist with an average particle size of 50 μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 (P < 0.05). The average diurnal stem sap flux density per unit projected leaf area (F) in silver birch (Betula pendula Roth.) trees was 24.8% (P < 0.05) and 27.2% (P < 0.01) higher in control (C) plots compared to humidification (H) plots during misting in 2008 and 2009, respectively. However, the difference between C and H plots was statistically insignificant (P > 0.05) in silver birch on the days without misting. In hybrid aspen (Populus tremula L. × P. tremuloides Michx.) the average difference in F between C and H plots was 61.1% (P < 0.001) during mist fumigation in the summer of 2009. Nevertheless, the difference was considerable (38.8%; P < 0.001) also on the days without misting, reflecting the impact of plant inner factors on F as a result of long-term acclimation to fumigation. The leaves of silver birch in a humidified plot demonstrated up to 2.4 °C lower (P < 0.05) leaf temperature (T_L) compared to the control plot in 2009. The decline in T_L decreased the humidity gradient between leaf and air by about 1/3, whereas 2/3 of the effect was caused directly by changes in air humidity in the leaf boundary layer. Our preliminary data suggest that the FAHM experimental facility enables water fluxes through a deciduous tree canopy to be reduced and this effect is attributable both to the increased air humidity and decreased leaf temperature. Changes in these two basic factors may create considerable differences in the physiology, anatomy and nutrition of a whole tree, also affecting forest functioning in the light of global climate change.     

Response of calcareous grassland vegetation to mowing and fluctuating weather conditions

Question: What determines the balance between the cover values of vascular plants, lichens and mosses in dry calcareous grassland communities? Location: Western Estonia. Methods: A five‐year (2001–2005) study was conducted in a dry calcareous grassland. The cover of mosses, lichens and vascular plants and all moss species was recorded in permanent plots. Vascular plants were cut in half of the plots. Data from a nearby weather station were used to calculate mean values of different weather parameters and a summer moisture index for the study years. Results: Significant differences in cover values between years were found. The fluctuations of total moss cover and the cover of the dominating moss species Ctenidium molluscum followed changes in annual precipitation. Both cover values were highest in years with high precipitation. The cover change of vascular plants was best characterized by the moisture index of the growth period (three summer months). Summers with high moisture indexes facilitated vascular plant and lichen growth. Annual precipitation and the cover of mosses had a negative influence on the cover of vascular plants. The cutting of vascular plants did not have a significant effect on moss and lichen cover. Conclusions: 1. On dry calcareous grasslands the growth of mosses is enhanced by high annual precipitation, while the growth of vascular plants and lichens is influenced rather by the high summer moisture index. The cover of vascular plants is inhibited by the large moss cover. 2. Mowing of vascular plants does not influence the cover of mosses and lichens.     

On testing hypotheses concerning standardized mortality ratios

This paper describes tests of hypotheses concerning the equality of any k standardized mortality ratios (or, equivalently, of any k indirect adjusted rates) from p(≥k) populations. The distinction is made between the situation where the standard population is chosen independently of the p populations and one where the standard is formed by pooling all p populations. Different test procedures are required for these two situations. When the pooled standard is used, the appropriate test procedure is applicable only when k = p. Experimental evidence is given showing that when the pooled standard is used both test procedures lead to the same conclusion concerning the hypothesis for the case k = p. The recommendation is made, therefore, to use the “incorrect” test procedure when the standard is a pooled one even when k < p.     

Interactions between ultraviolet light and interleukin-1 on MSH binding in both mouse melanoma and human squamous carcinoma cells

Interactions between beta-melanotropin (MSH), interleukin 1-a (IL-1), and ultraviolet light (UV) were examined in Cloudman S91 mouse melanoma and RHEK human squamous carcinoma cell lines. The following points were established: 1) both cell lines produced IL-1 and their production was stimulated by exposure of the cells to UV; 2) both cell lines possessed high affinity binding sites for MSH, and their ability to bind MSH was modulated by IL-1; 3) IL-1 exhibited both stimulatory and inhibitory effects on MSH binding to Cloudman cells; and 4) the stimulatory effect of IL-1 on MSH binding to melanoma cells was reflected in enhanced cellular responsiveness to MSH regarding tyrosinase activity (E.C. 1.14.18.1) and melanin content. The findings raise the possibility that interactions between keratinocytes and melanocytes may be regulated by IL-1 and MSH, and suggest a possible mechanism for stimulation of cutaneous melanogenesis by solar radiation: enhancement of MSH receptor activity by induction of IL-1.     

Some further remarks "on testing hypotheses concerning standardized mortality ratios"

In testing the equality of any k standardized mortality ratios from p(?k) populations, Kupper and Kleinbaum (1971) pointed out that different test procedures are required for the two situations where the standard population is chosen independently of the p populations and where the standard is formed by pooling all p populations. Unfortunately, the test they propose for the latter situation is applicable only when k = p. The purpose of this paper is to describe an alternative procedure based on the general theories of Wald (1943) and Neyman (1949) which can be used if the standard is a pooled one even when k < p.