Litmus Test


Litmus test (noun)– a test for acidity or alkalinity; a decisively indicative test

I recently learned about the four-fifths rule at work. The rule, suggested by the Equal Employment Opportunity Commission (EEOC) in its Uniform Guidelines, is the simplest and the most common way of assessing discrimination during a hiring process. I’ll use a simplified version of EEOC’s example to demonstrate how it works. Say there are 100 males and 50 females applying for a particular role. The company hires 20 of the male applicants (selection rate 20/100 = 20%) and 5 of the female applicants (selection rate 5/50 = 10%). If the selection rate ratios (10% : 20% = 1/2) is less than 4/5, then the four-fifths rule is violated. In our example, we could conclude that females are adversely impacted because 1/2 is less than 4/5.  There are issues regarding the four-fifths rule especially with small sample sizes, but I will not go into detail here. A colleague of mine compared the four-fifths rule to a litmus test as an assessment to quickly evaluate if adverse impact exists in a selection process.

In its original definition, litmus is a dye extracted from certain lichens. It is absorbed onto filter paper and into solution to produce pH indicators for testing acidity or alkalinity. Similar pigments can be found in red cabbage that also turn pink when coming in contact with acids and blue with bases. These pigments are called anthocyanins, which protect plants from ultraviolet light.

In addition to being an adverse impact assessment tool and a classic elementary science class experiment, litmus tests are used in the political realm often when appointing judges. For example, a president may look for a litmus test on Roe v. Wade (on the issue of abortion) for potential Supreme Court justice nominees. Criticisms for having a single-issue as a decision factor are frequently raised as one would expect.

On this election day, if one is so inclined to find out who their friends voted for, I don’t imagine finding a litmus test for it would be at all difficult.



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