1. Fixing the program my computer learned:
End-user debugging of
machine-learned programs
Dr Simone Stumpf
City University London
Simone.Stumpf.1@city.ac.uk

2. Bio
1996 BSc, Comp Sci w/ Cog Sci, UCL
2001 PhD Comp Sci, UCL
2001 - 2004 Research Fellow, UCL
2004 - 2007 Research Manager, Oregon State (OSU)
2007 - 2009 UX Architect, White Horse
2008 - present Asst Professor (Senior Research), OSU
2009 - present Lecturer, City University London
2

3. What are machine-learned programs?
•! Systems that “predict”
–! Spam filters, “smart desktops”, web page recommendations
•! Learn from and adapt to user after deployment
•! Probabilistic machine learning algorithms
•! Resulting behaviour is a program
How do you debug a program that was written by a machine
instead of a person? Especially when you don’t know much
about programming and are working with a program you
can’t even see?
3

4. A quick machine learning detour…
“Simple” algorithm like Naïve Bayes
–! Have input (features) and outputs (labels or classes)
–! From training data they learn a function: weight*input = class
–! As they further learn weights are changed
eg. spam filters (bag-of-words approach)
–! take all words appearing in the training data as features
–! throw out stop words (a, the, ?)
–! do stemming (walking, walked = walk)
–! learn how prevalent certain words are in spam messages
–! use that function to predict whether new email message is spam
4

5. Current debugging approach
Based on your interest in:
! ! ! "
We recommend:
5

6. Problems and opportunities for end users
•! Are not machine learning experts or programmers
•! Only they can fix if incorrect behaviour occurs
–! Cannot inspect source code
–! Can only observe results at run-time
–! Can usually only give more training examples to influence future
behaviour
–! Need to provide lots of training data to change behaviour
•! Much richer knowledge could be exploited
•! Could increase usability and trust
How can the program communicate its reasoning to the end
user? How could the user talk back?
6

7. Formative study
•! Enron email dataset folders (farmer-d): Personal, Resume,
Bankrupt, Enron News (122 messages)
•! Lo-fi prototypes with explanations
–! Rule-based
–! Similarity-based
–! Keyword-based
•! 13 participants, talk-aloud
7

8. Explanations by ML program
Simplified yet faithful
Concrete
•! Rule-based best understood but no clear overall preference
•! Serious understandability problems with Similarity-based
•! Negative keyword list with keyword-based problematic
(negative weights)
Matters if they they think reasoning is sound and it is
communicated clearly, word choices important
8

9. What does the user tell the program?
•! Select different features (53%)
–! It should put email in ‘Enron News’ if it has the keywords “changes”
and “policy”.
•! Adjust weights (12%)
–! The second set of words should be given more importance.
•! Parse/extract in different way (10%)
–! I think that it should look for typos in the punctuation for indicators
toward ‘Personal’.
•! Employ feature combinations (5%)
–! I think it would be better if it recognized a last and a first name
together.
•! Use relational features (4%)
–! This message should be in ‘EnronNews’ since it is from the
chairman of the company.
9

10. What knowledge do they use?
•! Commonsense (36%)
–! “Qualifications” would seem like a really good Resume word, I
wonder why that’s not down here.
•! English (30%)
–! Does the computer know the difference between “resumé” and
“resume”?
•! Domain (15%)
–! Different words could have been found in common like … “Ken
Lay”.
10

11. Putting it into practice…
Message List
Folders
Message
Explanation
11

12. Usability of prototype
•! System doesn’t heed user, learning too much or too little
•! “Unlearning” important
•! Users take care in selecting feedback but lack support to
make good choices
12

13. A why-oriented approach to debugging ML
Folders Message List Message
Why Questions
Explanation
13

14. Barriers for end users
•! All encountered barriers, Selection and Coordination most
prevalent
•! Some users get “stuck” within a Selection barrier loop
Systems need to support where to debug and the effects of
debugging
14

15. What helps end users debug?
•! What information regarding logic of a learned program is
particularly useful
•! Machine-learning saliency
–! exposure of useful and accurate pieces of information about the
logic of a machine-learned program
15

16. Study set-up
•! Domain of “coding” transcripts
•! 9 participants with coding experience
•! With and without explanations
16

17. Natural Programming approach
17

18. Saliency principles
•! SP1: Expose the ML Program’s Reasoning Process
–! Data (features)
–! Reasoning (probabilities, absence)
•! SP2: Support a Flexible Vocabulary
–! Word combinations, punctuation, relational information
–! Extensible by user
•! SP3: Illustrate Effects of User Changes
–! Impact of user actions
–! “sandbox”
18

19. The AutoCoder prototype
Prediction Confidence widget (W3), Impact
Machine-generated Explanation (W1),
Count Icons (W5), Popularity Bar
Absence Explanation (W2), User- (W7),
Change History Markers (W6).
generated Suggestion (W4)
19

20. Saliency study
•! 74 participants, no coding experience
•! 4 versions
–! Basic (VB): machine-generated explanations, user suggestions,
change history markers
–! Code-oriented (V1): Basic + Absence + Impact Count
–! Runtime-oriented (V2): Basic + Confidence + Popularity
–! Comprehensive (V3)
•! Each participant experienced two versions and two
transcripts
20

21. Saliency widgets useful for debugging
•! Explanations Most helpful
•! Confidence
•! Popularity
•! Change History
•! Impact Count
•! Absence Least helpful
•! Runtime version preferred over code-oriented,
combination of both clear winner
•! Problems with misinterpretation of Popularity
•! Demonstrates saliency principles are good starting point
21

22. Getting feedback from users….Great!
WHAT DO WE DO WITH IT?
22

23. Changing the machine’s reasoning
•! Simplest way: adjust feature weights
•! Constraint-based
–! No substantial improvements in accuracy
–! Hardness of constraints difficult to set
•! User co-training (new)
–! Exploits unlabeled data
–! Substantial improvements for some users, especially if no user
feedback approach resulted in low accuracy
–! Some losses for others
Quality of feedback matters otherwise there is “noise”
23

24. End-user feature engineering
•! Process of designing features for use by a ML algorithm
–! What to attend to/what counts as input
•! Critical for performance
•! Typically done by a machine learning expert with a domain
expert before deployment
24

25. Impact
•! Option 1: Add user-defined features to algorithm (+1%)
•! Option 2: Add them and weight them more heavily (-2.5%)
•! Higher increases for individuals with weighted approach
(+27%) but canceled out by individual decreases (-30%)
Need to spot unpredictive features (“noise”)
25

26. Identifying unpredictive features
•! Characteristic 1: Poor test data agreement
–! # of test segments with feature F and class label C divided by # of
test segments with feature F
•! Characteristic 2: Under-representation of a user-defined
feature in its assigned class in test data
–! # of test segments with feature F and class label C divided by # of
test segments with class label C
26

27. Evaluation and implications
•! Filtering features based on these characteristics
–! 94% of the 100 worst user-defined features can be filtered (but 64%
of 100 best user-defined features are removed)
–! 5% macro-F1 increase overall, 32.2% best individual increase for
Option 2
•! Can compute approximations in absence of much test data
•! Build user interface approaches to help identify when
unpredictive features are added
How much do we trust the user feedback? How much does
the ML algorithm trust itself?
27

28. Future Work
•! New explanations, new interfaces for new algorithms
–! Other approaches (recommender systems, neural nets etc)
•! Debugging strategies and debugging support
–! User competence models
–! ML Confidence models
–! User languages to change data and reasoning
–! Unlearning
–! Cost/Benefit
•! Learn from other users or “common sense”
28

29. Conclusion
•! New, exciting research area combining HCI and AI
•! Can make ML systems much smarter and quicker by
harnessing knowledge of end users
•! Increase usability of these systems for end users
29

30. Publications
•! S. Stumpf, V. Rajaram, L. Li, W. Wong, M. Burnett, T. Dietterich, E. Sullivan, and J. Herlocker,
"Interacting meaningfully with machine learning systems: Three experiments," Int. J. Hum.-Comput.
Stud., vol. 67, 2009, pp. 639-662.
•! T. Kulesza, W. Wong, S. Stumpf, S. Perona, R. White, M.M. Burnett, I. Oberst, and A.J. Ko, "Fixing
the program my computer learned: barriers for end users, challenges for the machine," Proceedings of
the 14th international conference on Intelligent user interfaces, Sanibel Island, Florida, USA: ACM,
2009, pp. 187-196.
•! S. Stumpf, E. Sullivan, E. Fitzhenry, I. Oberst, W. Wong, and M. Burnett, "Integrating rich user
feedback into intelligent user interfaces," Proceedings of the 13th international conference on
Intelligent user interfaces, Gran Canaria, Spain: ACM, 2008, pp. 50-59.
•! S. Stumpf, V. Rajaram, L. Li, M. Burnett, T. Dietterich, E. Sullivan, R. Drummond, and J. Herlocker,
"Toward harnessing user feedback for machine learning," Proceedings of the 12th international
conference on Intelligent user interfaces, Honolulu, Hawaii, USA: ACM, 2007, pp. 82-91.
30