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Das, Sourish
- Understanding Sea Ice Melting Via Functional Data Analysis
Abstract Views :291 |
PDF Views:89
Authors
Affiliations
1 Chennai Mathematical Institute, Chennai - 603103, IN
1 Chennai Mathematical Institute, Chennai - 603103, IN
Source
Current Science, Vol 115, No 5 (2018), Pagination: 920-929Abstract
We have addressed the problem of sea ice extent (SIE) melting for Arctic and Southern Ocean. The ‘satellite passive microwave remote sensing data’ for daily SIE over a year has been considered as a smooth continuous function, called functional data. The analysis of the mean function of SIE over the different year-blocks and 95% bootstrap confidence bands for Arctic Ocean shows a statistically significant drop in SIE. Additional evidence of SIE melting in the Arctic Ocean is provided through phase plane analysis. During the summer, the SIE is observed about 30% less in the current year-block than that of the first year-block.Keywords
Arctic Ocean, Bootstrap and Confidence Band, Mean Function, Sea Ice Extent, Southern Ocean.References
- Ramsay, J. O. and Silverman, B. W., Functional Data Analysis, Springer, 2nd edn, 2005.
- Wang, J.-L., Chiou, J.-M. and Müller, H.-G., Functional data analysis. Ann. Rev. Stat. Appl., 2016, 3, 257–295.
- Ramsay, J. O. and Silverman, B. W., Applied Functional Data Analysis: Methods and Case Studies, Springer, 2002, 2nd edn.
- Parkinson, C. L., Cavalieri, D. J., Gloersen, P., Zwally, H. J. and Comiso, J. C., Arctic sea ice extents, areas, and trends 1978–1996. J. Geophys. Res. Oceans, 1999, 104, 20837–20856.
- Johannessen, O. M., Shalina, E. V. and Miles, M. W., Satellite evidence for an Arctic sea ice cover in transformation. Science, 1999, 286, 1937–1939.
- Comiso, J. C., A rapidly declining perennial sea ice cover in the Arctic. Geophys. Res. Lett., 2002, 29(20), 17-1–17-4.
- Stroeve, J., Holland, M. M., Meier, W., Scambos, T. and Serreze, M. C., Arctic sea ice decline: faster than forecast. Geophys. Res. Lett., 2007, 34(9), 1–5.
- Comiso, J. C., Parkinson, C. L., Gersten, R. and Stock, L., Accelerated decline in the Arctic sea ice cover. Geophys. Res. Lett., 2008, 35(1), 1–5.
- Vihma, T., Effects of Arctic Sea ice decline on weather and climate: a review. Surv. Geophys., 2014, 35(5), 1175–1214.
- Josefino, C. C., Global changes in the sea ice cover and associated surface temperature changes. ISPRS – international archives of the photogrammetry. Remote Sensing Spatial Infor. Sci., 2016, XLIB8, 469–479.
- Ramsay, J. O., Wickham, H., Graves, S. and Hooker, G., Functional Data Analysis, 2014, R package v 2.4.4.
- Efron, B. and Tibshirani, R. J., An Introduction to the Bootstrap, CRC Press, 1st edn, 1994.
- Normalization of Marks in Multi-Session Examinations
Abstract Views :389 |
PDF Views:101
Authors
Affiliations
1 Indian Statistical Institute, New Delhi 110 016, IN
2 Chennai Mathematical Institute, Chennai 603 103, IN
1 Indian Statistical Institute, New Delhi 110 016, IN
2 Chennai Mathematical Institute, Chennai 603 103, IN
Source
Current Science, Vol 118, No 1 (2020), Pagination: 34-39Abstract
When a test is conducted in several sessions using distinct question papers, normalization of scores is required to have a fair assessment of the candidates. Several selection tests nowadays are conducted in multiple sessions (using multiple choice questions). In this article we discuss various normalization schemes used in India when an examination involving multiple choice questions is conducted across various sessions. We illustrate through simulation, that the percentile-based normalization scheme outperforms all the other schemes.Keywords
Multi-Session Examinations, Multiple Choice Questions, Normalization Schemes, Test Scores.References
- Baker, F., The Basics of Item Response Theory, ERIC Clearinghouse on Assessment and Evaluation, University of Maryland, MD, USA, 2001.
- Fox, J.-P., Bayesian Item Response Modeling: Theory and Applications, Springer, 2010.
- Takane, Y. and de Leeuw, On the relationship between item response theory and factor analysis of discretized variables J. Psychometr., 1987, 52, 393–408.