Spherical Cows
in Data Science
Scott Ernst
2016
Hypothetical Modeling & Simulation
Spherical Cows?
A Dairy Farmer
wants to increase milk production
He Asks 3 Experts for Advice
Physicist
Psychologist
Engineer
Engineer
"You need to increase milking efficiency.
Install larger tubes, retrofited pumps
and flow-optimized piping."
Psychologist
"Your cows need to be happier during milking.
Paint the stalls green."
Physicist
"If we assume a spherical cow..."
All Models Are Wrong
Some Models Are Useful
George Box
/All_models_are_wrong
Cunningly chosen
parsimonious models
George Box
/All_models_are_wrong
often do provide
remarkably useful approximations
Remember Fourier?
y(x) = A \cdot sin(x) + B \cdot sin(2x) + C \cdot sin(3x) + ...
Example: Dinosaurs
Example: Dinosaurs
Meaningful Differences?
Invalidated Previous Work
Is Economics Research Replicable? 60 Published Papers from 13 Journals Say ”Usually Not”
Finance and Economics Discussion Series
Divisions of Research & Statistics and Monetary Affairs
Federal Reserve Board, Washington, D.C.
http://www.federalreserve.gov/econresdata/feds/2015/files/2015083pap.pdf
Over half of psychology studies fail reproducibility test
The Reproducibility Project
& The Nature Publishing Group
https://osf.io/ezcuj/
Researchers often base their study design on implicit knowledge, without necessarily intending to ... This implicit process can push the results in one direction or another.
John Ioannidis, a biologist at Harvard in an investigation of the validity of published results
http://newmr.org/blog/most-published-research-findings-are-probably-false-john-ioannidis/
"most published research findings are probably false"
According to some estimates, three-quarters of published scientific papers in the field of machine learning are bunk...
Sandy Pentland, a computer scientist at the Massachusetts Institute of Technology.
http://www.economist.com/news/briefing/21588057-scientists-think-science-self-correcting-alarming-degree-it-not-trouble
Data Science
Preparation
1
Processing
2
Presentation
3
Failures Happen When...
Preparation
1
Processing
2
Presentation
3
-
Faulty collection
-
Unsound design
Preparation
1
Processing
2
Presentation
3
-
Misuse of tools/algorithms
-
Incorrectly groomed data
Failures Happen When...
Preparation
1
Processing
2
Presentation
3
-
Poor selection emphasis
Failures Happen When...
-
Bad layout and/or format
Overfitting
Karen Rubin Building a Quantitative Trading Strategy To Beat the S&P500 PyCon 2016: https://www.youtube.com/watch?v=ll6Tq-wTXXw
Spherical Cows
To The Rescue!
Hypothetical Modeling
& Simulation
OVERLOAD!
Don't Panic
Structure of a Simulation
1. Input
2. Evolve
3. Output
Settings / Configuration
Initial / Boundary Conditions
Computation
Modifies State Data
Calculations / Analysis
Save State Data
Example
Airplane Boarding
/File:Lufthansa_737_interior.jpg
Boeing 737
/File:American_Airlines.Boeing_737-800.LAX.2007.jpg
Boeing 737
Seating Chart
4 Rows
23 Rows
154 Passengers
Code & Results...
Time for the Details
Spherical Cows in Data Science
By sernst
