Wednesday, May 11, 2016

- Bias #10: Selection Bias, Reporting & Publishing



Wikipedia:
In the general case, selection biases cannot be overcome with statistical analysis of existing data alone, though Heckman correction may be used in special cases. An assessment of the degree of selection bias can be made by examining correlations between exogenous (background) variables and a treatment indicator. However, in regression models, it is correlation between unobserved determinants of the outcome and unobserved determinants of selection into the sample which bias estimates, and this correlation between unobservables cannot be directly assessed by the observed determinants of treatment.

The availability heuristic is a mental shortcut that relies on immediate examples that come to a given person's mind when evaluating a specific topic, concept, method or decision. The availability heuristic operates on the notion that if something can be recalled, it must be important, or at least more important than alternative solutions which are not as readily recalled.[1] Subsequently, under the availability heuristic, people tend to heavily weigh their judgments toward more recent information, making new opinions biased toward that latest news.[2]

The availability of consequences associated with an action is positively related to perceptions of the magnitude of the consequences of that action. In other words, the easier it is to recall the consequences of something the greater those consequences are often perceived to be. Most notably, people often rely on the content of their recall if its implications are not called into question by the difficulty that they experience in bringing the relevant material to mind.

io9:

Observational Selection Bias

This is that effect of suddenly noticing things we didn't notice that much before — but we wrongly assume that the frequency has increased. A perfect example is what happens after we buy a new car and we inexplicably start to see the same car virtually everywhere. A similar effect happens to pregnant women who suddenly notice a lot of other pregnant women around them. Or it could be a unique number or song. It's not that these things are appearing more frequently, it's that we've (for whatever reason) selected the item in our mind, and in turn, are noticing it more often. Trouble is, most people don't recognize this as a selectional bias, and actually believe these items or events are happening with increased frequency — which can be a very disconcerting feeling. It's also a cognitive bias that contributes to the feeling that the appearance of certain things or events couldn't possibly be a coincidence (even though it is).

The Present Moment Bias
We humans have a really hard time imagining ourselves in the future and altering our behaviors and expectations accordingly. Most of us would rather experience pleasure in the current moment, while leaving the pain for later. This is a bias that is of particular concern to economists (i.e. our unwillingness to not overspend and save money) and health practitioners. Indeed, a 1998 study showed that, when making food choices for the coming week, 74% of participants chose fruit. But when the food choice was for the current day, 70% chose chocolate. 

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