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Auflistung nach Autor:in "Nordgaard, Anders"

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  • Konferenzbeitrag
    Impact of Sampling Frequency on the Power of Nonparametric Tests for Water Quality Trends
    (The Information Society and Enlargement of the European Union, 2003) Nordgaard, Anders
    In this paper we assess the power of the Hirsch & Slack test for trend in water quality data from a number of small rivers in Sweden. In particular, we compare estimated power functions from tests applied to observations taken monthly and quarterly. The power function is estimated through a simulation study with data generated by bootstrap resampling in contrast with common methods based on the normal distribution. The results show a substantial loss in power when the sampling frequency is lowered from monthly to quarterly data. The loss depends on both the river and the variable analysed and this information can be transferred to optimisation procedures in the design of monitoring programs.
  • Konferenzbeitrag
    Variance Reduction for Trend Analysis of Hydrochemical Data in Brackish Waters
    (Environmental Communication in the Information Society - Proceedings of the 16th Conference, 2002) Libiseller, Claudia; Nordgaard, Anders
    We propose one parametric and one nonparametric method for conducting trend tests on nutrient concentrations in brackish waters taking into account that the temporal variation in both nitrogen and phosphorus records can be strongly influenced by the mixing of sea water and fresh water. Both methods utilise salinity as a covariate in the trend analysis. Data on total phosphorus in the Baltic Sea showed that there was a downward trend, although it was very weak when the natural fluctuations in salinity had been taken into account.