Oceanography Seminar- Edward Laws

February 12, 3:00pm - 4:00pm
Mānoa Campus, Marine Sciences Building, MSB 100 Add to Calendar

Edward Laws, Professor
School of Coast and Environment
Louisiana State University

“Bias in Ordinary Least Squares When the Independent Variable is Uncontrolled: Chlorophyll a and Photosynthetic Rates at Station ALOHA” It is well known that ordinary least squares (OLS) provides a biased estimate of the slope of the functional relationship between an independent variable X and a dependent variable Y if there are errors in X and if X is merely measured but not controlled. The errors in X typically include both measurement errors and natural variability. When Y is a function of more than one independent variable, the effect of the independent variables in addition to X on an OLS treatment of X versus Y is mathematically indistinguishable from the effect of errors in X. To argue that an OLS is unbiased when X is uncontrolled amounts to arguing that all the scatter in the data is due to errors in Y. A more likely scenario is that Y is a function of more than one independent variable, in which case repeated measurements of X will provide no clue as to the magnitude of the natural variability that impacts the OLS. I illustrate this conundrum by considering the relationship between chlorophyll a concentrations and photosynthetic rates at the Hawaii Ocean Time-series Station ALOHA, where variability of the productivity indices almost completely obscures the relationship between chlorophyll a concentrations and photosynthetic rates if the data are analyzed by OLS.


Event Sponsor
Oceanography, Mānoa Campus

More Information
Sharrese, (808) 956-7633, ocean@soest.hawaii.edu, http://www.soest.hawaii.edu/oceanography/seminar.html, Oceanography Seminar- Edward Laws (PDF)

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