Revealing Algorithmic Rankers

Julia Stoyanovich and Ellen P. Goodman in the Freedom to Tinker Blog: “ProPublica’s story on “machine bias” in an algorithm used for sentencing defendants amplified calls to make algorithms more transparent and accountable. It has never been more clear that algorithms are political (Gillespie) and embody contested choices (Crawford), and that these choices are largely obscured from public scrutiny (Pasquale and Citron). We see it in controversies over Facebook’s newsfeed, or Google’s search results, or Twitter’s trending topics. Policymakers are considering how to operationalize “algorithmic ethics” and scholars are calling for accountable algorithms (Kroll, et al.).

One kind of algorithm that is at once especially obscure, powerful, and common is the ranking algorithm (Diakopoulos). Algorithms rank individuals to determine credit worthiness, desirability for college admissions and employment, and compatibility as dating partners. They encode ideas of what counts as the best schools, neighborhoods, and technologies. Despite their importance, we actually can know very little about why this person was ranked higher than another in a dating app, or why this school has a better rank than that one. This is true even if we have access to the ranking algorithm, for example, if we have complete knowledge about the factors used by the ranker and their relative weights, as is the case for US News ranking of colleges. In this blog post, we argue that syntactic transparency, wherein the rules of operation of an algorithm are more or less apparent, or even fully disclosed, still leaves stakeholders in the dark: those who are ranked, those who use the rankings, and the public whose world the rankings may shape.

Using algorithmic rankers as an example, we argue that syntactic transparency alone will not lead to true algorithmic accountability (Angwin). This is true even if the complete input data is publicly available. We advocate instead for interpretability, which rests on making explicit the interactions between the program and the data on which it acts. An interpretable algorithm allows stakeholders to understand the outcomes, not merely the process by which outcomes were produced….

Opacity in algorithmic rankers can lead to four types of harms:

(1) Due process / fairness. The subjects of the ranking cannot have confidence that their ranking is meaningful or correct, or that they have been treated like similarly situated subjects. Syntactic transparency helps with this but it will not solve the problem entirely, especially when people cannot interpret how weighted factors have impacted the outcome (Source 2 above).

(2) Hidden normative commitments. A ranking formula implements some vision of the “good.” Unless the public knows what factors were chosen and why, and with what weights assigned to each, it cannot assess the compatibility of this vision with other norms. Even where the formula is disclosed, real public accountability requires information about whether the outcomes are stable, whether the attribute weights are meaningful, and whether the outcomes are ultimately validated against the chosen norms. Did the vendor evaluate the actual effect of the features that are postulated as important by the scoring / ranking mode? Did the vendor take steps to compensate for mutually-reinforcing correlated inputs, and for possibly discriminatory inputs? Was stability of the ranker interrogated on real or realistic inputs? This kind of transparency around validation is important for both learning algorithms which operate according to rules that are constantly in flux and responsive to shifting data inputs, and for simpler score-based rankers that are likewise sensitive to the data.

(3) Interpretability. Especially where ranking algorithms are performing a public function (e.g., allocation of public resources or organ donations) or directly shaping the public sphere (e.g., ranking politicians), political legitimacy requires that the public be able to interpret algorithmic outcomes in a meaningful way. At the very least, they should know the degree to which the algorithm has produced robust results that improve upon a random ordering of the items (a ranking-specific confidence measure). In the absence of interpretability, there is a threat to public trust and to democratic participation, raising the dangers of an algocracy (Danaher) – rule by incontestable algorithms.

(4) Meta-methodological assessment. Following on from the interpretability concerns is a meta question about whether a ranking algorithm is the appropriate method for shaping decisions. There are simply some domains, and some instances of datasets, in which rank order is not appropriate. For example, if there are very many ties or near-ties induced by the scoring function, or if the ranking is too unstable, it may be better to present data through an alternative mechanism such as clustering. More fundamentally, we should question the use of an algorithmic process if its effects are not meaningful or if it cannot be explained. In order to understand whether the ranking methodology is valid, as a first order question, the algorithmic process needs to be interpretable….

The Ranking Facts show how the properties of the 10 highest-ranked items compare to the entire dataset (Relativity), making explicit cases where the ranges of values, and the median value, are different at the top-10 vs. overall (median is marked with red triangles for faculty size and average publication count). The label lists the attributes that have most impact on the ranking (Impact), presents the scoring formula (if known), and explains which attributes correlate with the computed score. Finally, the label graphically shows the distribution of scores (Stability), explaining that scores differ significantly up to top-10 but are nearly indistinguishable in later positions.

Something like the Rankings Facts makes the process and outcome of algorithmic ranking interpretable for consumers, and reduces the likelihood of opacity harms, discussed above. Beyond Ranking Facts, it is important to develop Interpretability tools that enable vendors to design fair, meaningful and stable ranking processes, and that support external auditing. Promising technical directions include, e.g., quantifying the influence of various features on the outcome under different assumptions about availability of data and code, and investigating whether provenance techniques can be used to generate explanations….(More)”