PONE-D-20-02223

Tubes and Bubbles - Topological Confinement of YouTube Recommendations

PLOS ONE

Dear Dr. Roth,

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Tiago P. Peixoto

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PLOS ONE

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

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Reviewer #1: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: In this manuscript the authors approach the problem of how filter bubbles in online social systems can emerge as a result of the underlying recommendation system. For this they investigate the structure of networks obtained from following recommendations across videos on youtube. Specifically, the authors create and validate a new methodology for collecting such data and perform a detailed computational analysis of the obtained networks finding that i) networks contract as the seed videos become more popular, and ii) the dynamics of the random walks exhibit confinement.

This work makes a substantial contribution to recent and ongoing efforts to better understand the dynamics in socio-technical systems such as youtube which have become a major platform for dissemination and consumption of information. I like the innovative methodological approach taken by the authors to look under the hood of these recommendation systems via recommendation networks (and the rigor in validating it), especially given the fact that the underlying algorithms&data are not openly accessible. The statistical anaylsis is solid and the results are presented in an intelligible way. My main point of criticism is on the interpretation of the results in terms of the dynamics (see details below). I think it should be clarified that all conclusions come from correlational analysis and not from following the dynamics of individual videos over time in order to avoid misunderstandings. Pending corresponding revision, I fully recommend publication of the paper.

1. The results of mean entropy and number of pageviews is described as a graph contraction (line 217): "It appears that, as videos receive views, their overall recommendation graphs contract, becoming significantly smaller in number of nodes, while the diversity of the mean random walk increases."

The results in Figure 4 suggest a strong correlation between entropy and number of views. However, the conslusion as written suggests a dynamical process of indivdual videos which would only be justifieds from longitudinal studies.

2. In line 253 the authors refer to "audience effect" - I am not aware of a clear definition and couldnt find one in the manuscript. Perhaps the authors could clarify in order to avoid misunderstanding on what is meant.

3. In line 257 the authors claim that the measure of c is an intrinsic property of the video bc it is not correlated with explicit actions. I think this statement is a bit too strong in the absence of following individual videos over time.

4. In line 278 the authors claim that the dynamics is dominantly driven by the actions of the user. The dataset does not follow the dynamics of a video over time.

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Reviewer #1: Yes: Martin Gerlach

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Tubes and Bubbles - Topological Confinement of YouTube Recommendations

PONE-D-20-02223R1

Dear Dr. Roth,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

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With kind regards,

Tiago P. Peixoto

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The revised manuscript addresses all the concerns raised in my previous comments substantially improving the manuscript. I recommend publication of the manuscript in PLOS ONE.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #1: Yes: Martin Gerlach