Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering “BAD” DATA Sun e e e e 

Overview ä Bad Data ä Learning from unexpected results ä Isotherm Analysis ä Research ä Bad Data ä Learning from unexpected results ä Isotherm Analysis ä Research

Sources of “Bad” Data ä Error in preparation of samples ä mass or volume measurement error ä contamination ä improper storage ä sample substitution ä sample loss ä samples with high heterogeneity ä Apparatus failures ä leaks ä incompatible materials ä inadequate control of an important parameter ä Error in preparation of samples ä mass or volume measurement error ä contamination ä improper storage ä sample substitution ä sample loss ä samples with high heterogeneity ä Apparatus failures ä leaks ä incompatible materials ä inadequate control of an important parameter

Instrument Errors ä detector malfunction ä below detection limit or above maximum ä interference ä software (instrument or computer) ä hardware (analog to digital converter, power supply,...) ä calibration ä detector malfunction ä below detection limit or above maximum ä interference ä software (instrument or computer) ä hardware (analog to digital converter, power supply,...) ä calibration

More sources of “Bad Data” ä Error in data analysis ä numerical error (data entry) ä units (classic errors of factors of 10 and factors of 1000) ä incorrectly applied theory ä Error in theory ä Error in data analysis ä numerical error (data entry) ä units (classic errors of factors of 10 and factors of 1000) ä incorrectly applied theory ä Error in theory

Bad Data aren’t Bad! ä “Bad” data usually means the results were unexpected ä perhaps unorthodox! ä Copernicus “Concerning the Revolutions of the Celestial Bodies”1543 ä Papal Index of forbidden books until 1835 ä _____________________ ä Data do not lie! ä Data always mean something ä If you ignore data that you don’t understand you are missing an opportunity to learn ä “Bad” data usually means the results were unexpected ä perhaps unorthodox! ä Copernicus “Concerning the Revolutions of the Celestial Bodies”1543 ä Papal Index of forbidden books until 1835 ä _____________________ ä Data do not lie! ä Data always mean something ä If you ignore data that you don’t understand you are missing an opportunity to learn Bad data for 292 years!

Unexpected Results ä Lack of repeatability (poor precision) ä scatter for all data ä outlier ä systemic error ä Lack of repeatability (poor precision) ä scatter for all data ä outlier ä systemic error

Unexpected Results ä Inconsistent with theory ä mass balances indicate loss or gain of mass ä inconsistent with previous results ä Inconsistent with theory ä mass balances indicate loss or gain of mass ä inconsistent with previous results Sun e e

Responses to Unexpected Results ä Determine accuracy of technique by analyzing known samples ä Determine precision of technique by analyzing replicates ä Evaluate propagation of errors through analysis ä are you trying to measure the difference between two large numbers? ä is the precision of the measurement similar to the magnitude of the estimate? ä Are you not controlling an important parameter? ä Is the parameter that you are studying insignificant? ä Determine accuracy of technique by analyzing known samples ä Determine precision of technique by analyzing replicates ä Evaluate propagation of errors through analysis ä are you trying to measure the difference between two large numbers? ä is the precision of the measurement similar to the magnitude of the estimate? ä Are you not controlling an important parameter? ä Is the parameter that you are studying insignificant?

Isotherm Analysis Pointers ä Units ä Express mass of VOC in grams ä Express concentrations as g per mL ä Remember GC injection volume was 0.1 mL ä Use names to keep track of parameters in spreadsheet ä Build sheet from left to right ä Units ä Express mass of VOC in grams ä Express concentrations as g per mL ä Remember GC injection volume was 0.1 mL ä Use names to keep track of parameters in spreadsheet ä Build sheet from left to right

More Pointers ä Soil density = 1.6 g/mL ä Soil moisture content is 13% ä Soil mass was close to 20 g ä Analyze the 4 data sets as sets ä Use the data from one group to calculate a single value for each parameter ä You will get 4 estimates for each parameter ä Soil density = 1.6 g/mL ä Soil moisture content is 13% ä Soil mass was close to 20 g ä Analyze the 4 data sets as sets ä Use the data from one group to calculate a single value for each parameter ä You will get 4 estimates for each parameter spreadsheet

Why is a small f s a measurement problem?

EPICS Error Analysis water low solubility high solubility ä Assume 10% error in measuring gas concentrations ä What are the maximum and minimum values of mass in liquid phase? ä Assume 10% error in measuring gas concentrations ä What are the maximum and minimum values of mass in liquid phase? (10 ± 1) – (9 ± 0.9) 11 – 8.1 = – 9.9 = -0.9 (10 ± 1) –( 1 ± 0.1) 11 – 0.9 = – 1.1 = 7.9