Oh oh, I Have Another Favourite Statistic!


Mahalanobis

The Mahalanobis Distance
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This is a lovely little statistic that folks should take advantage of a lot more. If you’re doing a lot of survey data quality work, you should know about the Mahalanobis Distance (MD). It can help you decide whether a responder is answering questions honestly or not simply by comparing their set of responses to other sets of responses. If someone responds to a series of questions in a way that doesn’t match how other people are responding, then that set of data gets picked out.
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So, MD finds people who are straightlining because straightlining is usually not a normal way to respond to data. Of course, finding straightliners is easy to do anyways so who cares. BUT, and far more importantly, this statistic helps to pick out random responders, people who are just haphazardly clicking all over the place. You can find random responders if you read through an individual’s responses, but it takes a lot more personal attention. MD does it automatically, instantly, without all that extra time.
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If you’d like to have a read that goes way over most people’s heads, follow this link to “On the generalised distance in statistics” by P.C. Mahalanobis.
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Oh, and I have the coolest story to go along with this. I MET THE GREAT NIECE OF MAHALANOBIS HIMSELF!!!! In fact, she and I were coworkers for a short while. I did my best to discover all the amazing details that one might want to know about her celebrity uncle, you know, things like his favourite colour or his favourite brand of ketchup, but she respected his privacy and refused to budge. I did manage to get an AUTOGRAPHED (by my friend Renee) copy of his publication though.
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Ok, ok, maybe I shouldn’t get all excited about it, but I am. And if you think that’s just silly, well you’re just jealous.
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