Module 3: Risk and Risk Factors Flashcards
What is algorithmic bias?
Algorithmic bias is a systemic deviation of an algorithm’s output, performance, or impact relative to some norm, aim, standard, or baseline.
What is explicit vs. implicit bias?
In the former case, the algorithm’s developer intentionally projects its own biases into the algorithm, leading to biased outputs. In the latter case, bias creeps in undetected through the algorithm’s design or via the data used to train the algorithm. In those cases, bias is implicit and unintended.
What two main approaches to fairness are applied in the context of AI?
Individual fairness relates to the Aristotelian doctrine of “treating like cases alike.” In other words, it demands similarly situated individuals be treated equally. We avoid direct discrimination on the basis of protected characteristics, such as race, gender, or religion.
Group fairness, on the other hand, does not consider individuals, but instead looks at statistical differences between groups.
What is demographic parity? Does it need to exhibit correct predictions?
Demographic parity requires that the distribution of predictions is identical across subpopulations.
Demographic parity is entirely independent of the true value (Y). In other words, it does not consider if the predictions are correct, only if the predictions are equally distributed.
What is a drawback of demographic parity?
Using demographic parity is inappropriate for a given task, such as when base rates significantly differ between groups, and those differences are relevant to the decision at hand.
How is algorithmic accuracy calculated and is it always useful?
Accuracy denotes the fraction of correct predictions.
Especially in cases of unbalanced data, accuracy is not a good measure.
E.g. There are 100 job applicants, 10 of whom are suitable, 90 of whom are not. Imagine now the algorithm correctly classifies the 90 applicants as unsuitable (TN), but also classifies the 10 suitable candidates as unsuitable (FN). In this case the algorithm would have an accuracy of 90% even though it would only provide the user with a single output: unsuitable.
What is Predictive Rate Parity ?
In some contexts, such as medical diagnostics or credit lending, the cost of false positives is high, and thus accuracy of the predictions for the positive or negative class is important. In other words, we want to maximize the positive predictive value (PPV) or precision
Positive Predictive Value (PPV) or Precision = TP / (TP+FP)
PPV is an important concept for algorithmic performance evaluation. It denotes the proportion of correctly predicted positive outcomes.
We can now define another fairness measure, predictive rate parity, which is satisfied when PPV is equal across subpopulations.
What is a downside of Predictive Rate Parity?
A downside of predictive rate parity is that it does not account for differences in base rates across groups. If base rates differ significantly, then achieving predictive rate parity becomes extremely challenging and can have adverse effects on algorithmic performance.
What is sensitivity and how is it calculated?
Sensitivity is important to know in case of rare events how well the prediction performs. It is also known as True Positive Rate.
Sensitivity = TP / (TP + FN)
Maximizing sensitivity requires us to minimize false negatives.
What is the difference between PPV and Sensitivity?
Whereas PPV measured the proportion of correctly predicted positives to all positive predictions, sensitivity measures the proportion of correctly predicted positives to all actual positives.
What is equal opportunity and how is it measured?
If sensitivity is the same across groups, we have achieved equal opportunity, which is the last important fairness measure we discuss here. Equal opportunity ensures that individuals of each group have an equal chance of being correctly identified as positive.
In the case of equal opportunity, the equality constraint is only applied to the true positive rate, so that each group has the same opportunity of being granted a positive outcome. A more-restrictive version of equal opportunity is equalized odds, where we not only require equality of sensitivity across groups, but also equality of specificity
What is specificity and how is it calculated?
Specificity captures the proportion of actual negatives that are identified as such
Specificity = TN / (TN+FP)
Can all three notions of fairness be achieved?
Unfortunately, a mathematical theorem demonstrates that doing so is impossible. Specifically, when base rates between populations are different, which is almost always the case, then it is impossible to satisfy demographic parity, predictive rate parity, and equal opportunity simultaneously.
Assign the following labels to the statements
Accuracy ; PPV / Precision ; Sensitivity ; Demographic Parity ; Predictive Rate Parity ; Equal Opportunity
“Of all cases, how many did we correctly identify as either positive or negative?”
Of all positively predicted cases, how many were actually positive?”
“Of all actual positive cases, how many did we correctly identify as such?”
“Is the likelihood of a positive prediction the same across groups?”
“Is the likelihood of a true positive prediction the same across groups?”
“Is the likelihood of being positive when predicted to be positive the same across groups?”
Accuracy “Of all cases, how many did we correctly identify as either positive or negative?”
Positive predictive value/Precision “Of all positively predicted cases, how many were actually positive?”
Sensitivity “Of all actual positive cases, how many did we correctly identify as such?”
Demographic parity “Is the likelihood of a positive prediction the same across groups?”
Predictive rate parity “Is the likelihood of a true positive prediction the same across groups?”
Equal opportunity “Is the likelihood of being positive when predicted to be positive the same across groups?”
What is required for problem specification?
Problem specification always requires us to have some degree of familiarity with the domain and needs in question. In other words, domain expertise is a necessary (though not sufficient) condition for good problem specification.
Which statistical property is causing an issue with the removal of protected characteristics from the estimation process?
Endogeneity refers to situations in which the error term in a model is correlated with the predictor variable. In simpler terms, it refers to situations in which there are hidden or overlooked correlations that are not captured by the model in question.
If protected criteria are correlated with features of a model, then the omission of the protected criteria can lead to bias in the estimated feature coefficients
Why is proxying of concepts by features problematic?
1) Some concepts cannot be easily operationalized (e.g. team work) and their omission or misspecification can lead to bias
2) We need to be careful that the construction of proxies does not lead to bias (e.g. productivity measured as the total output while protected groups might have the same work per time rate but lower total output)
What is a problem with learning from past data in supervised learning in the context of protected groups?
Past data can have biases that will be reproduced when the algorithm is trained on the data
What are potential solutions (with their drawbacks) how to deal with the situation when protected group characteristics are correlated with features?
We could simply remove all correlated variables but much of the time, these variables are highly relevant for prediction, and the algorithm would perform much worse if we removed them.
Another solution could be to include the protected variable when we model our relationship but then not use it in the prediction step, and instead substitute it with an average. This would only slightly decrease accuracy but ensure that (a) people who are alike in all relevant respects but have different protected characteristics are treated the same, and (b) correlated variables are not contaminated by the protected variables. However, as previously mentioned, care needs to be taken to ensure legality
What is representation bias?
The collected sample is not representative of the target population and can result in problematic model specifications. Performance can be particularly low for groups that are at the intersection of different, underrepresented subgroups.
What is measurement bias?
When measurement methods are not consistent across the sample. If a doctor spends more time meeting with and evaluating wealthy patients, resulting data on the likelihood of early-stage disease discovery may be biased in favor of that group.
Why does a representative sample might bias against minority groups?
Given the statistical nature of both supervised and unsupervised learning algorithms, these algorithms deliver the statistically ideal output. For example, consider a medical training set of patients, 3% of whom are pregnant women who would require different treatment. It is likely that the algorithm would significantly underperform for this group because there are many fewer data points.