SOM clustering of 21-year data of a small pristine boreal lake

In order to improve our understanding of the connections between the biological processes and abiotic factors, we clustered complex long-term ecological data with the self-organizing map (SOM) technique. The available 21-year long (1990–2010) data set from a small pristine humic lake, in southern Finland, consisted of 27 meteorological, physical, chemical, and biological variables. The SOM grouped the data into three categories of which the first one was the largest with 12 variables, including metabolic processes, dissolved oxygen, total nitrogen and phosphorus, chlorophyll a, and taxonomical groups of plankton known to exist in spring. The second cluster comprised of water temperature and precipitation together with cyanobacteria, algae, rotifers, and crustacean zooplankton, an association emphasized with summer. The third cluster was consisted of six physical and chemical variables linked to autumn, and to the effects of inflow and/or water column mixing. SOM is a useful method for grouping the variables of such a large multi-dimensional data set, especially, when the purpose is to draw comprehensive conclusions rather than to search for associations across sporadic variables. Sampling should minimize the number of missing values. Even flexible statistical techniques, such as SOM, are vulnerable to biased results due to incomplete data.Peer reviewe

Associating spatial patterns of zooplankton abundance with water temperature, depth, planktivorous fish and chlorophyll

201

Lipoprotein(a) is not associated with venous thromboembolism risk

<p><i>Objectives.</i> Evidence from case-control studies as well as meta-analyses of these study designs suggest elevated lipoprotein(a) [Lp(a)] to be associated with an increased risk of venous thromboembolism (VTE). Prospective evidence on the association is limited, uncertain, and could be attributed to regression dilution bias. We aimed to assess the prospective association of Lp(a) with risk of VTE and correct for regression dilution. <i>Design.</i> We related plasma Lp(a) concentrations to the incidence of VTE in 2,180 men of the Kuopio Ischemic Heart Disease cohort study. Hazard ratios (HRs) (95% confidence intervals [CI]) were assessed and repeat measurements of Lp(a) at 4 and 11 years from baseline, were used to correct for within-person variability. <i>Results.</i> After a median follow-up of 24.9 years, 110 validated VTE cases were recorded. The regression dilution ratio of log_e Lp(a) adjusted for age was 0.85 (95% CI: 0.82–0.89). In analyses adjusted for several established risk factors and potential confounders, the HR (95% CI) for VTE per 1 SD (equivalent to 3.56-fold) higher baseline log_e Lp(a) was 1.06 (0.87–1.30). In pooled analysis of five population-based cohort studies (including the current study) comprising 66,583 participants and 1314 VTE cases, the fully-adjusted corresponding HR for VTE was 1.00 (95% CI: 0.94–1.07), with no evidence of heterogeneity between studies. <i>Conclusions.</i> Primary analysis as well as pooled evidence from previous studies suggest circulating Lp(a) is not prospectively associated with future VTE risk, indicating that evidence of associations demonstrated in case-control designs may be driven by biases such as selection bias.</p