Survivorship bias, or survival bias, is the logical error of concentrating on the people or things that “survived” some process and inadvertently overlooking those that did not because of their lack of visibility. This can lead to false conclusions in several different ways. The survivors may be actual people, as in a medical study, or could be companies or research subjects or applicants for a job, or anything that must make it past some selection process to be considered further.
Survivorship bias can lead to overly optimistic beliefs because failures are ignored, such as when companies that no longer exist are excluded from analyses of financial performance. It can also lead to the false belief that the successes in a group have some special property, rather than just coincidence. For example, if three of the five students with the best college grades went to the same high school, that can lead one to believe that the high school must offer an excellent education. This could be true, but the question cannot be answered without looking at the grades of all the other students from that high school, not just the ones who “survived” the top-five selection process.
First published in 1982, it is one of the biggest selling business books ever, selling 3 million copies in its first four years, and being the most widely held monograph in the United States from 1989 to 2006 (WorldCat data).
The book purports to explore the art and science of management used by several 1980s companies.
Hindsight bias, also known as the knew-it-all-along effect or creeping determinism, is the inclination, after an event has occurred, to see the event as having been predictable, despite there having been little or no objective basis for predicting it, prior to its occurrence.[1][2] It is a multifaceted phenomenon that can affect different stages of designs, processes, contexts, and situations.[3] Hindsight bias may cause memory distortion, where the recollection and reconstruction of content can lead to false theoretical outcomes. It has been suggested that the effect can cause extreme methodological problems while trying to analyze, understand, and interpret results in experimental studies. A basic example of the hindsight bias is when, after viewing the outcome of a potentially unforeseeable event, a person believes he or she “knew it all along”. Such examples are present in the writings of historians describing outcomes of battles, physicians recalling clinical trials, and in judicial systems trying to attribute responsibility and predictability of accidents.
Non verbal expressions of power and dominance are gestures or motions that assert one´s authority over another.
handshakes
waving
smiling
The colors one wears affect other´s perceptions of one´s authority:
purple: people of high status adorn their clothing with purple to distinguish themselves as noble or wealthy
people attribute greater authority to others wearing red
It is human to strive for power and dominance in social settings
simple gestures establish authority
A firmer handshake
Better posture
Causing slight interruptions in conversation
can rise authority in group situations
many peers view Non verbal expressions of power and dominance as manipulation for self gain
Their abuse can be disastrous
Men and women have different perceptions of Non verbal expressions of power and dominance
Nodding is misinterpreted in cross gender communication
women interpret a nod as a signal of understanding
men interpret a nod as a signal of agreement
small miscommunications and misinterpretations lead to disagreement and confrontation
Russel (as cited in Dunbar & Burgoon, 2005) describes, “the fundamental concept in social science is power, in the same way that energy is the fundamental concept in physics“. Power and dominance-submission are two key concepts in relationships, especially close relationships where individuals rely on one another to achieve their goals (Dunbar & Burgoon, 2005) and as such it is important to be able to identify indicators of dominance.
Power and dominance are different concepts yet share similarities. Power is the ability to influence behavior (Bachrach & Lawler; Berger; Burgoon et al.; Foa & Foa; French & Raven; Gray-Little & Burks; Henley; Olson & Cromwell; Rollins & Bahr, as cited in Dunbar & Burgoon, 2005) and may or may not be fully evident until challenged by an equal force (Huston, as cited in Dunbar & Burgoon, 2005). Unlike power, that may be latent, dominance is manifest reflecting individual (Komter, as cited in Dunbar & Burgoon, 2005), situational and relationship patterns where control attempts are either accepted or rejected (Rogers-Millar & Millar,as cited in Dunbar & Burgoon, 2005). Moskowitz, Suh, and Desaulniers (1994) mention two similar ways that people can relate to the world in interpersonal relationships: agency and communion. Agency includes status and is a continuum from assertiveness-dominance to passive-submissiveness – it can be measured by subtracting submissiveness from dominance. Communion is a second way to interact with others and includes love with a continuum from warm-agreeable to cold-hostile-quarrelsomeness. Power and dominance relate together in such a way that those with the greatest and least power typically do not assert dominance while those with more equal relationships make more control attempts Dunbar & Burgoon, 2005).
As one can see, power and dominance are important, intertwined, concepts that greatly impact relationships. In order to understand how dominance captures relationships one must understand the influence of gender and social roles while watching for verbal and nonverbal indicators of dominance.
The wagon-wheel effect (alternatively, stagecoach-wheel effect, stroboscopic effect) is an optical illusion in which a spokedwheelappears to rotate differently from its true rotation. The wheel can appear to rotate more slowly than the true rotation, it can appear stationary, or it can appear to rotate in the opposite direction from the true rotation. This last form of the effect is sometimes called thereverse rotation effect.
The wagon-wheel effect is most often seen in film or television depictions of stagecoaches or wagons in Western movies, although recordings of any regularly spoked wheel will show it, such as helicopter rotors and aircraftpropellers. In these recorded media, the effect is a result of temporal aliasing.[1] It can also commonly be seen when a rotating wheel is illuminated by flickering light. These forms of the effect are known as stroboscopic effects: the original smooth rotation of the wheel is visible only intermittently. A version of the wagon-wheel effect can also be seen under continuous illumination.
Rushton (1967[5]) observed the wagon-wheel effect under continuous illumination while humming. The humming vibrates the eyes in their sockets, effectively creating stroboscopic conditions within the eye. By humming at a frequency of a multiple of the rotation frequency, he was able to stop the rotation. By humming at slightly higher and lower frequencies, he was able to make the rotation reverse slowly and to make the rotation go slowly in the direction of rotation. A similar stroboscopic effect is now commonly observed by people eating crunchy foods, such as carrots, while watching TV: the image appears to shimmer.[6] The crunching vibrates the eyes at a multiple of the frame rate of the TV. Besides vibrations of the eyes, the effect can be produced by observing wheels via a vibrating mirror. Rear-view mirrors in vibrating cars can produce the effect.
Truly continuous illumination
The first to observe the wagon-wheel effect under truly continuous illumination (such as from the sun) was Schouten (1967[7]). He distinguished three forms of subjective stroboscopy which he called alpha, beta, and gamma: Alpha stroboscopy occurs at 8–12 cycles per second; the wheel appears to become stationary, although “some sectors [spokes] look as though they are performing a hurdle race over the standing ones” (p. 48). Beta stroboscopy occurs at 30–35 cycles per second: “The distinctness of the pattern has all but disappeared. At times a definite counterrotation is seen of a grayish striped pattern” (pp. 48–49). Gamma stroboscopy occurs at 40–100 cycles per second: “The disk appears almost uniform except that at all sector frequencies a standing grayish pattern is seen … in a quivery sort of standstill” (pp. 49–50). Schouten interpreted beta stroboscopy, reversed rotation, as consistent with there being Reichardt detectors in the human visual system for encoding motion. Because the spoked wheel patterns he used (radial gratings) are regular, they can strongly stimulate detectors for the true rotation, but also weakly stimulate detectors for the reverse rotation.
There are two broad theories for the wagon-wheel effect under truly continuous illumination. The first is that human visual perception takes a series of still frames of the visual scene and that movement is perceived much like a movie. The second is Schouten’s theory: that moving images are processed by visual detectors sensitive to the true motion and also by detectors sensitive to opposite motion from temporal aliasing. There is evidence for both theories, but the weight of evidence favours the latter.
Discrete frames theory
Purves, Paydarfar, and Andrews (1996[8]) proposed the discrete-frames theory. One piece of evidence for this theory comes from Dubois and VanRullen (2011[9]). They reviewed experiences of users of LSD who often report that under the influence of the drug a moving object is seen trailing a series of still images behind it. They asked such users to match their drug experiences with movies simulating such trailing images viewed when not under the drug. They found that users selected movies around 15–20 Hz. This is between Schouten’s alpha and beta rates.
Other evidence for the theory is reviewed next.
Temporal aliasing theory
Kline, Holcombe, and Eagleman (2004[10]) confirmed the observation of reversed rotation with regularly spaced dots on a rotating drum. They called this “illusory motion reversal”. They showed that these occurred only after a long time of viewing the rotating display (from about 30 seconds to as long as 10 minutes for some observers). They also showed that the incidences of reversed rotation were independent in different parts of the visual field. This is inconsistent with discrete frames covering the entire visual scene. Kline, Holcombe, and Eagleman (2006[11]) also showed that reversed rotation of a radial grating in one part of the visual field was independent of superimposed orthogonal motion in the same part of the visual field. The orthogonal motion was of a circular grating contracting so as to have the same temporal frequency as the radial grating. This is inconsistent with discrete frames covering local parts of visual scene. Kline et al. concluded that the reverse rotations were consistent with Reichardt detectors for the reverse direction of rotation becoming sufficiently active to dominate perception of the true rotation in a form of rivalry. The long time required to see the reverse rotation suggests that neural adaptation of the detectors responding to the true rotation has to occur before the weakly stimulated reverse-rotation detectors can contribute to perception.
Some small doubts about the results of Kline et al. (2004) sustain adherents of the discrete-frame theory. These doubts include Kline et al.’s finding in some observers more instances of simultaneous reversals from different parts of the visual field than would be expected by chance, and finding in some observers differences in the distribution of the durations of reversals from that expected by a pure rivalry process (Rojas, Carmona-Fontaine, López-Calderón, & Aboitiz, 2006[12]).
In 2008, Kline and Eagleman demonstrated that illusory reversals of two spatially overlapping motions could be perceived separately, providing further evidence that illusory motion reversal is not caused by temporal sampling.[13] They also showed that illusory motion reversal occurs with non-uniform and non-periodic stimuli (for example, a spinning belt of sandpaper), which also cannot be compatible with discrete sampling. Kline and Eagleman proposed instead that the effect results from a “motion during-effect”, meaning that a motion after-effect becomes superimposed on the real motion.
Dangers
Because of the illusion this can give to moving machinery, it is advised that single-phase lighting be avoided in workshops and factories. For example, a factory that is lit from a single-phase supply with basic fluorescent lighting will have a flicker of twice the mains frequency, either at 100 or 120 Hz (depending on country); thus, any machinery rotating at multiples of this frequency may appear to not be turning. Seeing that the most common types of AC motors are locked to the mains frequency, this can pose a considerable hazard to operators of lathes and other rotating equipment. Solutions include deploying the lighting over a full 3-phase supply, or by using high-frequency controllers that drive the lights at safer frequencies.[14] Traditional incandescent light bulbs, which employ filaments that glow continuously, offer another option as well, albeit at the expense of increased power consumption. Smaller incandescent lights can be used as task lighting on equipment to help combat this effect to avoid the cost of operating larger quantities of incandescent lighting in a workshop environment.
