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Efficiency Improvement of
Neutrality-Enhanced Recommendation
Toshihiro Kamishima*, Shotaro Akaho*, Hideki Asoh*, and Jun Sakuma†
*National Institute of Advanced Industrial Science and Technology (AIST), Japan
†University of Tsukuba, Japan; and Japan Science and Technology Agency
Workshop on Human Decision Making in Recommender Systems
In conjunction with the RecSys 2013 @ Hong Kong, China, Oct. 12, 2013
1START
Overview
2
Providing neutral information is important in recommendation
Information-neutral Recommender System
This system makes recommendation so as to enhance
the neutrality from a viewpoint feature specified by a user
The absolutely neutral recommendation is intrinsically infeasible,
because recommendation is always biased in a sense that it is
arranged for a specific user
avoidance of biased recommendation
fair treatment of content suppliers or item providers
adherence to laws and regulations in recommendation
Outline
3
Introduction
Recommendation Neutrality
Viewpoint feature, Intuitive definition
Applications of Recommendation Neutrality
Avoidance of biased recommendation, Fair treatment of content
providers, Adherence to laws and regulations
Information-neutral Recommendation System
pmf model, information-neutral recommender system, neutrality
terms
Experiments
small data, genre-wise mean differences, larger data
Discussion about the Recommendation Neutrality
subjectivity & objectivity, recommendation diversity, privacy-
preserving data mining, and more
Conclusion
Recommendation Neutrality
4
Viewpoint Feature
5
V : viewpoint feature
It is specified by a user depending on his/her purpose
Recommendation results are neutral from this viewpoint
Its value is determined depending on a user, an item, and their
features
As in a case of standard recommendation, we use random variables
X: a user, Y: an item, and R: a rating value
In this talk, a viewpoint feature is restricted to a binary type
We adopt an additional variable for the recommendation neutrality
Ex. viewpoint = user’s gender / movie’s release year
Recommendation Neutrality
6
Whether a movie is new or old does not influence
the inference of whether the movie is recommended or not
Ex. viewpoint = movie’s release year
Recommendation Neutrality
Recommendation results are neutral if no information about a given
viewpoint feature does not influence the results
The status of the specified viewpoint feature is explicitly excluded
from the inference of the results
If movies A and B are the same except for their release year,
the movie A is always recommended when the movie B is recommended,
and vice versa
Applications of
the Recommendation Neutrality
7
Avoidance of Biased Recommendation
8
Biased Recommendation
exclude a good candidate from a set of options
rate relatively inferior options higher
The Filter Bubble Problem
Pariser posed a concern that personalization technologies narrow and
bias the topics of information provided to people
http://www.thefilterbubble.com/
Biased Recommendations can lead to inappropriate decisions
Filter Bubble
9
[TED Talk by Eli Pariser]
Friend recommendation list in Facebook
To fit for Pariser’s preference, conservative people are eliminated
from his recommendation list, while this fact is not noticed to him
viewpoint = a political conviction of a friend candidate
Whether a candidate is conservative or progressive
does not influence whether he/she is included in a friend list or not
Fair Treatment of Content Providers
10
System managers should fairly treat their content providers
The US FTC has been investigating Google to determine whether the
search engine ranks its own services higher than those of competitors
Ranking in a list retrieved by search engines
Content providers are managers’ customers
For marketplace sites, their tenants are customers, and these tenants
must be treated fairly when recommending the tenants’ products
viewpoint = a content provider of a candidate item
Information about who provides a candidate item is ignored,
and providers are treated fairly
[Bloomberg]
Adherence to Laws and Regulations
11
Recommendation services must be managed
while adhering to laws and regulations
suspicious placement keyword-matching advertisement
Advertisements indicating arrest records were more frequently
displayed for names that are more popular among individuals of
African descent than those of European descent
viewpoint = users’ socially sensitive demographic information
Legally or socially sensitive information
can be excluded from the inference process of recommendation
Socially discriminative treatments must be avoided
[Sweeney 13]
Information-neutral
Recommender System
12
Information-neutral Recommender System
13
Information-neutral Recommender System
neutral from a specified viewpoint feature
A penalty term enhances the recommendation neutrality
Information-neutral version of a probabilistic matrix factorization model
+
high prediction accuracy
Accurate prediction is achieved by minimizing an empirical error
ˆr(x, y) = µ + bx + cy + pxq>
y
Probabilistic Matrix Factorization
14
Probabilistic Matrix Factorization Model
predict a preference rating of an item y rated by a user x
well-performed and widely used
cross effect of
users and itemsglobal bias
user-dependent bias item-dependent bias
For a given training data set (xi: user, yi: item, ri: rating), model
parameters are learned by minimizing the squared loss function with a
L2 regularizer
[Salakhutdinov 08, Koren 08]
Information-neutral PMF Model
15
information-neutral version of a PMF model
adjust ratings according to the state of a viewpoint
incorporate dependency on a viewpoint variable
enhance the neutrality of a score from a viewpoint
add a neutrality function as a constraint term
adjust ratings according to the state of a viewpoint
Multiple models are built separately, and each of these models
corresponds to the each value of a viewpoint feature
When predicting ratings, a model is selected according to the value
of viewpoint feature
viewpoint feature
ˆr(x, y, v) = µ(v)
+ b(v)
x + c(v)
y + p(v)
x q(v)
y
>
Neutrality Term and Objective Function
16
Parameters are learned by minimizing this objective function
squared loss function neutrality term L2 regularizer
regularization
parameter
neutrality parameter to control the balance
between the neutrality and accuracy
X
D
(ri ˆr(xi, yi, vi))
2
+ ⌘ neutral(R, V ) + k⇥k2
2
neutrality term, : quantify the degree of neutralityneutral(R, V )
It depends on both ratings and view point features
The larger value of the neutrality term indicates that the higher level
of the neutrality
Objective Function of an Information-neutral PMF Model
enhance the neutrality of a rating from a viewpoint feature
Formal Definition of
the Recommendation Neutrality
17
Recommendation Neutrality
Recommendation results are neutral if no information about a given
viewpoint feature does not influence the results
the statistical independence
between a rating variable, R, and a viewpoint feature, V
Two types of neutrality terms
I(R; V ) =
X
R,V
Pr[R, V ] log
Pr[R|V ]
Pr[R]
Mutual Information Calders&Verwer’s Score
k Pr[R|V = 0] Pr[R|V = 1]k
Pr[R|V ] = Pr[R] ⌘ R ?? V
Mutual Information
18
mi-hist (mutual information - histogram)
This term cannot differentiate analytically
Optimization is too slow to process even the moderate size of data
[Kamishima 12]
Neutrality Term in Our Previous Work
I(R; V ) ⇡
1
|D|
X
(ri,vi)2D
log
Pr[ˆri|vi]
P
v2{0,1} Pr[ˆri|v] Pr[v]
Pr[r|v] =
1
|D|
X
(x,y)2D
Pr[r|x, y, v]
too complex
modeling by a histogram
Calders&Verwer’s Score (CV Score)
19
Our New Neutrality Term
analytically differentiable and efficient in optimization
make two distributions of R given V = 0 and 1 similar
m-match r-match
Matching means of predicted
ratings when V = 0 and V = 1
k Pr[R|V = 0] Pr[R|V = 1]k
(MeanD(0) [ˆr] MeanD(1) [ˆr])
2
X
(x,y)2D
(ˆr(x, y, 0) ˆr(x, y, 1))
2
Matching two predicted ratings
when V = 0 and V =1,
regardless of the actual value of V
Experiments
20
(Results were improved from those in an proceeding article)
Small Data Set
21
to compare mi-hist and m-match/r-match terms
General Conditions
9,409 use-item pairs are sampled from the Movielens 100k data set
(the mi-hist term cannot process larger than this data set)
the number of latent factor K = 1 (due to the small size of data)
regularization parameter λ=1 (more finely tuned than that in an article)
Evaluation measures are calculated by using five-fold cross validation
Evaluation Measure
MAE (mean absolute error)
prediction accuracy
Random recommendation: MAE=0.903
Original PMF recommendation: MAE=0.759
NMI (normalized mutual information)
the neutrality of a predicted ratings from a specified viewpoint
Viewpoint Featues
22
The older movies have a tendency to be rated higher, perhaps because
only masterpieces have survived [Koren 2009]
“Year” viewpoint : movie’s release year is newer than 1990 or not
“Gender” viewpoint : a user is male or female
The movie rating would depend on the user’s gender
mi-hist
m-match
r-match
0.70
0.75
0.80
0.01 0.1 1 10 100
mi-hist
m-match
r-match
10
−4
10
−3
10
−2
10
−1
0.01 0.1 1 10 100
neutrality parameter η : the lager value enhances the neutrality more
Small Data & Year Viewpoint
23
moreaccurate
moreneutral
neutrality (NMI)accuracy (MAE)
As the increase of a neutrality parameter η,
prediction accuracies were worsened slightly in all cases,
the neutralities were enhanced drastically in mi-hist/m-match, cases but
not in a r-match case
both m-hist and m-match successfully enhanced the neutrality
As the increase of a neutrality parameter η,
both the accuracy and neutrality did not largely change
mi-hist
m-match
r-match
10
−4
10
−3
10
−2
10
−1
0.01 0.1 1 10 100
mi-hist
m-match
r-match
0.70
0.75
0.80
0.01 0.1 1 10 100
neutrality parameter η : the lager value enhances the neutrality more
Small Data & Gender Viewpoint
24
moreaccurate
moreneutral
neutrality (NMI)accuracy (MAE)
the neutrality was originally high and failed to improve further
Genre-wise Differences of Mean Ratings
25
To examine how the recommendation patterns are changed
Data were firstly divided according to their 18 kinds of movies’ genres
Each genre-wise data were further divided into two sets according to
their view-point value
mean ratings were computed for each set, and we showed the
differences of between mean ratings for two different values of V
Computation Procedure
Not provided in a proceeding article
Three Types of Ratings
the original true ratings in training data
ratings predicted by the PMF model with the mi-hist and m-match
terms, respectively (η = 100)
Genre-wise Differences of Mean Ratings
26
original mi-hist m-match
Children’s -0.229 -0.132 -0.139
Animation -0.224 -0.064 -0.068
Romance -0.122 -0.073 -0.073
Documentary 0.333 0.103 0.084
Horror 0.479 0.437 0.409
Fantasy 0.783 0.433 0.387
Gender: males’ mean ratings - females’ mean ratings
the positive values indicate genres more highly rated by males
Differences are basically narrowed by the neutrality enhancement
INRS didn’t simply shift the ratings, and changes were different
genre-wise
NMIs were not changed for a Gender case, but recommendation
patterns were surely changed
Large Data Set
27
to show that m-match and r-match terms are
applicable to larger data sets
General Conditions
The Movielens 1M data set (larger than that in an article)
mi-hist model cannot process this size of data set
the number of latent factor K = 7
regularization parameter λ = 1
Evaluation measures are calculated by using five-fold cross
validation
Baseline Accuracies
Random recommendation: MAE=0.934
Original PMF recommendation: MAE=0.685
m-match
r-match
0.65
0.70
0.75
0.01 0.1 1 10 100
m-match
r-match
10
−4
10
−3
10
−2
10
−1
0.01 0.1 1 10 100
neutrality parameter η : the lager value enhances the neutrality more
Large Data & Year Viewpoint
28
moreaccurate
moreneutral
neutrality (NMI)accuracy (MAE)
As the increase of a neutrality parameter η,
accuracies were more steeply worsened in a r-match case
the neutralities were improved in a m-match, but not in a r-match case
m-match succeed, but r-match failed
m-match
r-match
0.65
0.70
0.75
0.01 0.1 1 10 100
m-match
r-match
10
−4
10
−3
10
−2
10
−1
0.01 0.1 1 10 100
As the increase of a neutrality parameter η,
accuracies were similarly worsened in both cases
neutralities were successfully improved in a m-match case, but not in
a r-match case
the m-match term performed slightly better than the small data case
neutrality parameter η : the lager value enhances the neutrality more
Large Data & Gender Viewpoint
29
moreaccurate
moreneutral
neutrality (NMI)accuracy (MAE)
Discussion about
the Recommendation Neutrality
30
Objectivity and Subjectivity
31
Subjective Neutrality
Reviewers pointed out the
importance of testing how
users perceive the neutrality
Objective Neutrality
The neutrality is currently
evaluated by objective criteria
The neutrality should be guaranteed based on objective criteria
If users perceive the neutrality in recommendation, but it is truly
biased, such a recommender system would be a very dangerous tool
for big brothers to control users
showing the neutrality indexes, such as mutual information
comparing original recommendations and information-neutral ones
listing items in parallel under the conditions a viewpoint feature is a
original and is another value
possible tools for displaying the neutrality in recommendation
Recommendation Diversity
32
Recommendation Diversity
Similar items are not recommended in a sigle list, to a sigle user, to
all users, or in a temporally successive lists
[Ziegler+ 05, Zhang+ 08, Latha+ 09, Adomavicius+ 12]
Diversity Neutrality
Items that are similar in a
specified metric are excluded
from recommendation results
Information about a viewpoint
feature is excluded from
recommendation results
The mutual relations
among results
The relation between
results and viewpoints
recommendation list
similar items
excluded
Privacy-preserving Data Mining
33
recommendation results, R, and viewpoint features, V,
are statistically independent
In a context of privacy-preservation
Even if the information about R is disclosed,
the information about V will not exposed
mutual information between recommendation results, R,
and viewpoint features, V, is zero
I(R; V) = 0
In particular, a notion of the t-closeness has strong connection
More Recommendation Neutrality
34
Trade-offs between the accuracy and neutrality
red-lining effect
Information usable for inferring recommendation decreases in an INRS
where F is all information about other than V
Available information is non-increasing by enhancing the neutrality
Even if a feature V is eliminated from prediction model,
the information of V cannot excluded
the information of V is contained in the other correlated features
I(R; V, F) I(R; F) = I(X; V | F) 0
Conclusion
35
Our Contributions
We formulate the recommendation neutrality from a specified
viewpoint feature
We developed a recommender system that can enhance the
recommendation neutrality
The efficiency in optimization was drastically improved
Our experimental results show that the neutrality is successfully
enhanced without seriously sacrificing the prediction accuracy
Future Work
An INRS for non-binary viewpoint features
Information neutral version of generative recommendation models,
such as a pLSA / LDA model
program codes and data sets
http://www.kamishima.net/inrs/
acknowledgements
We would like to thank for providing a data set for the Grouplens
research lab
This work is supported by MEXT/JSPS KAKENHI Grant Number
16700157, 21500154, 23240043, 24500194, and 25540094
36

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Efficiency Improvement of Neutrality-Enhanced Recommendation

  • 1. Efficiency Improvement of Neutrality-Enhanced Recommendation Toshihiro Kamishima*, Shotaro Akaho*, Hideki Asoh*, and Jun Sakuma† *National Institute of Advanced Industrial Science and Technology (AIST), Japan †University of Tsukuba, Japan; and Japan Science and Technology Agency Workshop on Human Decision Making in Recommender Systems In conjunction with the RecSys 2013 @ Hong Kong, China, Oct. 12, 2013 1START
  • 2. Overview 2 Providing neutral information is important in recommendation Information-neutral Recommender System This system makes recommendation so as to enhance the neutrality from a viewpoint feature specified by a user The absolutely neutral recommendation is intrinsically infeasible, because recommendation is always biased in a sense that it is arranged for a specific user avoidance of biased recommendation fair treatment of content suppliers or item providers adherence to laws and regulations in recommendation
  • 3. Outline 3 Introduction Recommendation Neutrality Viewpoint feature, Intuitive definition Applications of Recommendation Neutrality Avoidance of biased recommendation, Fair treatment of content providers, Adherence to laws and regulations Information-neutral Recommendation System pmf model, information-neutral recommender system, neutrality terms Experiments small data, genre-wise mean differences, larger data Discussion about the Recommendation Neutrality subjectivity & objectivity, recommendation diversity, privacy- preserving data mining, and more Conclusion
  • 5. Viewpoint Feature 5 V : viewpoint feature It is specified by a user depending on his/her purpose Recommendation results are neutral from this viewpoint Its value is determined depending on a user, an item, and their features As in a case of standard recommendation, we use random variables X: a user, Y: an item, and R: a rating value In this talk, a viewpoint feature is restricted to a binary type We adopt an additional variable for the recommendation neutrality Ex. viewpoint = user’s gender / movie’s release year
  • 6. Recommendation Neutrality 6 Whether a movie is new or old does not influence the inference of whether the movie is recommended or not Ex. viewpoint = movie’s release year Recommendation Neutrality Recommendation results are neutral if no information about a given viewpoint feature does not influence the results The status of the specified viewpoint feature is explicitly excluded from the inference of the results If movies A and B are the same except for their release year, the movie A is always recommended when the movie B is recommended, and vice versa
  • 8. Avoidance of Biased Recommendation 8 Biased Recommendation exclude a good candidate from a set of options rate relatively inferior options higher The Filter Bubble Problem Pariser posed a concern that personalization technologies narrow and bias the topics of information provided to people http://www.thefilterbubble.com/ Biased Recommendations can lead to inappropriate decisions
  • 9. Filter Bubble 9 [TED Talk by Eli Pariser] Friend recommendation list in Facebook To fit for Pariser’s preference, conservative people are eliminated from his recommendation list, while this fact is not noticed to him viewpoint = a political conviction of a friend candidate Whether a candidate is conservative or progressive does not influence whether he/she is included in a friend list or not
  • 10. Fair Treatment of Content Providers 10 System managers should fairly treat their content providers The US FTC has been investigating Google to determine whether the search engine ranks its own services higher than those of competitors Ranking in a list retrieved by search engines Content providers are managers’ customers For marketplace sites, their tenants are customers, and these tenants must be treated fairly when recommending the tenants’ products viewpoint = a content provider of a candidate item Information about who provides a candidate item is ignored, and providers are treated fairly [Bloomberg]
  • 11. Adherence to Laws and Regulations 11 Recommendation services must be managed while adhering to laws and regulations suspicious placement keyword-matching advertisement Advertisements indicating arrest records were more frequently displayed for names that are more popular among individuals of African descent than those of European descent viewpoint = users’ socially sensitive demographic information Legally or socially sensitive information can be excluded from the inference process of recommendation Socially discriminative treatments must be avoided [Sweeney 13]
  • 13. Information-neutral Recommender System 13 Information-neutral Recommender System neutral from a specified viewpoint feature A penalty term enhances the recommendation neutrality Information-neutral version of a probabilistic matrix factorization model + high prediction accuracy Accurate prediction is achieved by minimizing an empirical error
  • 14. ˆr(x, y) = µ + bx + cy + pxq> y Probabilistic Matrix Factorization 14 Probabilistic Matrix Factorization Model predict a preference rating of an item y rated by a user x well-performed and widely used cross effect of users and itemsglobal bias user-dependent bias item-dependent bias For a given training data set (xi: user, yi: item, ri: rating), model parameters are learned by minimizing the squared loss function with a L2 regularizer [Salakhutdinov 08, Koren 08]
  • 15. Information-neutral PMF Model 15 information-neutral version of a PMF model adjust ratings according to the state of a viewpoint incorporate dependency on a viewpoint variable enhance the neutrality of a score from a viewpoint add a neutrality function as a constraint term adjust ratings according to the state of a viewpoint Multiple models are built separately, and each of these models corresponds to the each value of a viewpoint feature When predicting ratings, a model is selected according to the value of viewpoint feature viewpoint feature ˆr(x, y, v) = µ(v) + b(v) x + c(v) y + p(v) x q(v) y >
  • 16. Neutrality Term and Objective Function 16 Parameters are learned by minimizing this objective function squared loss function neutrality term L2 regularizer regularization parameter neutrality parameter to control the balance between the neutrality and accuracy X D (ri ˆr(xi, yi, vi)) 2 + ⌘ neutral(R, V ) + k⇥k2 2 neutrality term, : quantify the degree of neutralityneutral(R, V ) It depends on both ratings and view point features The larger value of the neutrality term indicates that the higher level of the neutrality Objective Function of an Information-neutral PMF Model enhance the neutrality of a rating from a viewpoint feature
  • 17. Formal Definition of the Recommendation Neutrality 17 Recommendation Neutrality Recommendation results are neutral if no information about a given viewpoint feature does not influence the results the statistical independence between a rating variable, R, and a viewpoint feature, V Two types of neutrality terms I(R; V ) = X R,V Pr[R, V ] log Pr[R|V ] Pr[R] Mutual Information Calders&Verwer’s Score k Pr[R|V = 0] Pr[R|V = 1]k Pr[R|V ] = Pr[R] ⌘ R ?? V
  • 18. Mutual Information 18 mi-hist (mutual information - histogram) This term cannot differentiate analytically Optimization is too slow to process even the moderate size of data [Kamishima 12] Neutrality Term in Our Previous Work I(R; V ) ⇡ 1 |D| X (ri,vi)2D log Pr[ˆri|vi] P v2{0,1} Pr[ˆri|v] Pr[v] Pr[r|v] = 1 |D| X (x,y)2D Pr[r|x, y, v] too complex modeling by a histogram
  • 19. Calders&Verwer’s Score (CV Score) 19 Our New Neutrality Term analytically differentiable and efficient in optimization make two distributions of R given V = 0 and 1 similar m-match r-match Matching means of predicted ratings when V = 0 and V = 1 k Pr[R|V = 0] Pr[R|V = 1]k (MeanD(0) [ˆr] MeanD(1) [ˆr]) 2 X (x,y)2D (ˆr(x, y, 0) ˆr(x, y, 1)) 2 Matching two predicted ratings when V = 0 and V =1, regardless of the actual value of V
  • 20. Experiments 20 (Results were improved from those in an proceeding article)
  • 21. Small Data Set 21 to compare mi-hist and m-match/r-match terms General Conditions 9,409 use-item pairs are sampled from the Movielens 100k data set (the mi-hist term cannot process larger than this data set) the number of latent factor K = 1 (due to the small size of data) regularization parameter λ=1 (more finely tuned than that in an article) Evaluation measures are calculated by using five-fold cross validation Evaluation Measure MAE (mean absolute error) prediction accuracy Random recommendation: MAE=0.903 Original PMF recommendation: MAE=0.759 NMI (normalized mutual information) the neutrality of a predicted ratings from a specified viewpoint
  • 22. Viewpoint Featues 22 The older movies have a tendency to be rated higher, perhaps because only masterpieces have survived [Koren 2009] “Year” viewpoint : movie’s release year is newer than 1990 or not “Gender” viewpoint : a user is male or female The movie rating would depend on the user’s gender
  • 23. mi-hist m-match r-match 0.70 0.75 0.80 0.01 0.1 1 10 100 mi-hist m-match r-match 10 −4 10 −3 10 −2 10 −1 0.01 0.1 1 10 100 neutrality parameter η : the lager value enhances the neutrality more Small Data & Year Viewpoint 23 moreaccurate moreneutral neutrality (NMI)accuracy (MAE) As the increase of a neutrality parameter η, prediction accuracies were worsened slightly in all cases, the neutralities were enhanced drastically in mi-hist/m-match, cases but not in a r-match case both m-hist and m-match successfully enhanced the neutrality
  • 24. As the increase of a neutrality parameter η, both the accuracy and neutrality did not largely change mi-hist m-match r-match 10 −4 10 −3 10 −2 10 −1 0.01 0.1 1 10 100 mi-hist m-match r-match 0.70 0.75 0.80 0.01 0.1 1 10 100 neutrality parameter η : the lager value enhances the neutrality more Small Data & Gender Viewpoint 24 moreaccurate moreneutral neutrality (NMI)accuracy (MAE) the neutrality was originally high and failed to improve further
  • 25. Genre-wise Differences of Mean Ratings 25 To examine how the recommendation patterns are changed Data were firstly divided according to their 18 kinds of movies’ genres Each genre-wise data were further divided into two sets according to their view-point value mean ratings were computed for each set, and we showed the differences of between mean ratings for two different values of V Computation Procedure Not provided in a proceeding article Three Types of Ratings the original true ratings in training data ratings predicted by the PMF model with the mi-hist and m-match terms, respectively (η = 100)
  • 26. Genre-wise Differences of Mean Ratings 26 original mi-hist m-match Children’s -0.229 -0.132 -0.139 Animation -0.224 -0.064 -0.068 Romance -0.122 -0.073 -0.073 Documentary 0.333 0.103 0.084 Horror 0.479 0.437 0.409 Fantasy 0.783 0.433 0.387 Gender: males’ mean ratings - females’ mean ratings the positive values indicate genres more highly rated by males Differences are basically narrowed by the neutrality enhancement INRS didn’t simply shift the ratings, and changes were different genre-wise NMIs were not changed for a Gender case, but recommendation patterns were surely changed
  • 27. Large Data Set 27 to show that m-match and r-match terms are applicable to larger data sets General Conditions The Movielens 1M data set (larger than that in an article) mi-hist model cannot process this size of data set the number of latent factor K = 7 regularization parameter λ = 1 Evaluation measures are calculated by using five-fold cross validation Baseline Accuracies Random recommendation: MAE=0.934 Original PMF recommendation: MAE=0.685
  • 28. m-match r-match 0.65 0.70 0.75 0.01 0.1 1 10 100 m-match r-match 10 −4 10 −3 10 −2 10 −1 0.01 0.1 1 10 100 neutrality parameter η : the lager value enhances the neutrality more Large Data & Year Viewpoint 28 moreaccurate moreneutral neutrality (NMI)accuracy (MAE) As the increase of a neutrality parameter η, accuracies were more steeply worsened in a r-match case the neutralities were improved in a m-match, but not in a r-match case m-match succeed, but r-match failed
  • 29. m-match r-match 0.65 0.70 0.75 0.01 0.1 1 10 100 m-match r-match 10 −4 10 −3 10 −2 10 −1 0.01 0.1 1 10 100 As the increase of a neutrality parameter η, accuracies were similarly worsened in both cases neutralities were successfully improved in a m-match case, but not in a r-match case the m-match term performed slightly better than the small data case neutrality parameter η : the lager value enhances the neutrality more Large Data & Gender Viewpoint 29 moreaccurate moreneutral neutrality (NMI)accuracy (MAE)
  • 31. Objectivity and Subjectivity 31 Subjective Neutrality Reviewers pointed out the importance of testing how users perceive the neutrality Objective Neutrality The neutrality is currently evaluated by objective criteria The neutrality should be guaranteed based on objective criteria If users perceive the neutrality in recommendation, but it is truly biased, such a recommender system would be a very dangerous tool for big brothers to control users showing the neutrality indexes, such as mutual information comparing original recommendations and information-neutral ones listing items in parallel under the conditions a viewpoint feature is a original and is another value possible tools for displaying the neutrality in recommendation
  • 32. Recommendation Diversity 32 Recommendation Diversity Similar items are not recommended in a sigle list, to a sigle user, to all users, or in a temporally successive lists [Ziegler+ 05, Zhang+ 08, Latha+ 09, Adomavicius+ 12] Diversity Neutrality Items that are similar in a specified metric are excluded from recommendation results Information about a viewpoint feature is excluded from recommendation results The mutual relations among results The relation between results and viewpoints recommendation list similar items excluded
  • 33. Privacy-preserving Data Mining 33 recommendation results, R, and viewpoint features, V, are statistically independent In a context of privacy-preservation Even if the information about R is disclosed, the information about V will not exposed mutual information between recommendation results, R, and viewpoint features, V, is zero I(R; V) = 0 In particular, a notion of the t-closeness has strong connection
  • 34. More Recommendation Neutrality 34 Trade-offs between the accuracy and neutrality red-lining effect Information usable for inferring recommendation decreases in an INRS where F is all information about other than V Available information is non-increasing by enhancing the neutrality Even if a feature V is eliminated from prediction model, the information of V cannot excluded the information of V is contained in the other correlated features I(R; V, F) I(R; F) = I(X; V | F) 0
  • 35. Conclusion 35 Our Contributions We formulate the recommendation neutrality from a specified viewpoint feature We developed a recommender system that can enhance the recommendation neutrality The efficiency in optimization was drastically improved Our experimental results show that the neutrality is successfully enhanced without seriously sacrificing the prediction accuracy Future Work An INRS for non-binary viewpoint features Information neutral version of generative recommendation models, such as a pLSA / LDA model
  • 36. program codes and data sets http://www.kamishima.net/inrs/ acknowledgements We would like to thank for providing a data set for the Grouplens research lab This work is supported by MEXT/JSPS KAKENHI Grant Number 16700157, 21500154, 23240043, 24500194, and 25540094 36