Monthly Archives: December 2015
When it comes to digital methods, one of the basic conundrums one encounters is the ambivalence between platform and practice. To phrase it in basic terms: are outcomes genuine human practice or simply artifacts of the platform’s affordances? There are different ways to approach this problem conceptually and I would go as far as saying that it is a false problem, since I do not think that there is something like unmediated human practice in the first place. The fact remains, however, that we may want to focus on one or the other for various reasons. My own interest lie squarely in understanding the technical dimension and this post introduces an approach to studying the algorithms at work in social media platforms with the help of digital methods.
While a number of scholars have recently been engaged in attempts to reverse engineer relevant algorithms, the objects I am interested in are clearly too complex and dynamic to reproduce the decision mechanisms involved – which, in any case, are probably in constant movement due to machine learning components being part of the larger procedure. My goal is actually more basic and the approach I want to present is largely descriptive in the sense that it does little more than propose a way to talk about the outcomes of algorithmic work, in this case of ranking mechanisms. By “talk about”, I first mean graphically and quantitatively, but the goal, in fact, is quite qualitative. While I have real sympathies for the desire to describe artifacts considered to be the apogee of exactness in exact terms, I think that we need to explore other directions as well. In any case, we constantly examine and analyze phenomena in ways that do not require formal descriptions. We can study the NY Times’ editorial decisions – which involve a lot of ranking and appreciation of value – in ways that do not include building a formal decision model and still make interesting observations. Maybe it is time to see how methods for describing social phenomena can be used to describe formal mechanisms and not the other way round. What I have in mind does not go very far in this direction, but it embraces description as its methodology.
To make this idea more plastic, I take YouTube (YT) as my example and focus on YT’s search ranking. When looking for the keyword [syria], for example, YT returns an ordered list of videos. How can we talk about the produced rankings, here? One way would be to look into the factors YT itself communicates as relevant or turn to SEO blogs to gather attempts to identify the central variables. This is certainly interesting, but we could also just look at the results themselves. Using the YouTube Data Tools (YTDT), I have been collecting daily rankings for a number of keywords over the last months, [syria] being one of them. This file contains the data for five days. The rows are videos ordered by result rank and there is also a viewcount for each video. The file looks like this:
A very basic way to start making sense of these results is to visualize them. To help with this, I built a small tool, RankFlow, which is explicitly designed for analyzing rankings over time. Here is a screenshot of a visualization of the data (click for larger image):
Every column is a day of videos and each column is ordered by result rank. The height of each block encodes the viewcount variable as logarithm (to compress the vast differences in viewcount) while colors (from blue to red) indicate the unprocessed viewcount. The video with the highest viewcount actually only appears at rank 15 on the fifth day. What can we learn from such a basic visualization? First, absolute viewcount is obviously not the main ranking criterion. Second, rankings change quite a lot; between the second and the third day, for example, seven videos fall out of the top 15 and the video that comes in first on day three is again gone on day five. Third, there are a number of videos in the top ranks that have surprisingly low viewcounts. What I take from this case – and others I have looked at – is that YT probably uses a predictive ranking model that calculates something like a “chance to find an audience” metric (e.g. based on channels’ previous videos), places the video in the rankings, and – if it does not catch on – removes it again quite quickly (the top video on the first day is good example for a video that does catch on). This is in stark contrast to the “authoritative” rankings on Google Search that change much less frequently and tend towards something like a stable consensus. On YT, the ranking mechanism seems to “care” much more about quick turnover, newness, and serendipity. Looking at a simple RankFlow can give us a pretty good idea what is happening with a specific query and looking at a number of them can lead us to a more general assessment about output dynamics.
A second approach to describing ranking follows a direction that uses an algorithm to talk about another algorithm’s output. The problem with the above visualization is that it quickly gets very complicated to read and summarize when we start adding columns. But information scientists have been working on ways to produce quantitative measures to describe changes in rankings. On the bottom of the above visualization, you can see a number that tries to measure the changes between each two day pairs. There are many such measures available, but the one I found most intriguing came from a 2010 paper by William Webber, Alistair Moffat, and Justin Zobel. This was the one metric I found that would a) work with ranked lists where elements are not necessarily the same for each list (i.e. a video present on one day is no longer there on the next day), b) take into account changes in rank, not just presence or absence of an element, and c) attribute more value to changes at the top of the list than changes happening at the bottom. Rank-Biased Overlap (and its metrical form, Rank-Biased Distance) does just that. The RBD value between two days thus interprets changes in rank in a particular way and it condenses its interpretation into a single value. The higher the value, the more change. This is, of course, a reductionist gesture, but if we understand how the metric reduces, it can be extremely helpful to make sense of the “changiness” of rankings in a context where we have a lot of data. The algorithm (equation 32 in the paper, the “calc_rbo” function in my implementation) is not simple, but if you take some time to compare the visualization to the RBD values, you can get a basic feel for how it reacts to changes in rankings. This opens the door to more “macro” appreciations of changes in ranking and, interestingly, to comparison between platforms. A high average RBD value would indicate a tendency to fluctuate, a low value a preference for stability.
Both of these examples do not allow us to reverse engineer the actual algorithm(s) in question, but we need to get comfortable with the idea that this is not going to be an option in most cases anyways. Systematic description, however, allows us to still say something about the structure and dynamics of outputs and gives us an idea of the character or temperament of a ranking mechanism, for example. This post is just a starting point that I hope to turn into something more substantial in the future, but I hope it shows how relatively simple techniques can be employed to make potentially interesting findings.