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Movements, leaders, victories and the continuing fight for equality.
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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
Time-saving bias is a concept that describes people's tendency to misestimate the time that could be saved (or lost) when increasing (or decreasing) speed.[1][2]
In general, people underestimate the time that could be saved when increasing from a relatively low speed—e.g., 25 mph (40 km/h) or 40 mph (64 km/h)—and overestimate the time that could be saved when increasing from a relatively high speed—e.g., 55 mph (89 km/h) or 90 mph (140 km/h). People also underestimate the time that could be lost when decreasing from a low speed and overestimate the time that could be lost when decreasing from a high speed.
In one study, participants were asked to judge which of two road improvement plans would be more efficient in reducing mean journey time. Respondents preferred a plan that would increase the mean speed from 70 to 110 km/h (43 to 68 mph) more than a plan that would increase the mean speed from 30 to 40 km/h (19 to 25 mph), although the latter actually saves more time.[3]
In another study, drivers were asked to indicate how much time they felt could be saved when increasing from either a low (30 mph (48 km/h)) or high (60 mph (97 km/h)) speed.[4] For example, participants were asked the following question: "You are driving along an open road. How much time do you feel you would gain if you drove for 10 miles [16 km] at 40 mph [64 km/h] instead of 30 mph [48 km/h]?".[5] Another question had a higher starting speed of 60 mph (97 km/h), and two other questions asked about losing time when decreasing speed, from either 30 or 60 mph (48 or 97 km/h).
Results supported the predictions of the time-saving bias, as participants underestimated the time saved when increasing from a low speed and overestimated the time saved when increasing from a relatively high speed. In addition, participants also misestimated the time lost when decreasing speed: they generally underestimated the time lost when decreasing from a low speed and overestimated the time lost when decreasing from a relatively high speed.[4]
The physical formula for calculating the time, , gained when increasing speed is:
Where is constant and used to transform between units of measurement, is the time gained, is the distance traveled and and are the original and increased speeds, respectively. This formula shows the relationship between increasing speed and journey time is curvilinear: a similar speed increase would result in more time saved when increasing from a low speed compared to a higher speed. For example, when increasing 20 to 30 mph (32 to 48 km/h) the time required to complete 10 miles (16 km) decreases from 30 to 20 minutes, saving 10 minutes. However, the same speed increase of 10 mph (16 km/h) would result in less time saved if the initial speed is higher—e.g., only 2 minutes saved when increasing from 50 to 60 mph (80 to 97 km/h). Changing the distance of the journey from 10 miles (16 km) to a longer or shorter distance will increase or decrease these time savings, but will not affect the relationship between speed and time savings.
Svenson suggested that people's judgments of time-savings actually follow a Proportion heuristic, by which people judge the time saved as the proportion of the speed increase from the initial speed.[6] Another study suggested that people might follow a simpler difference heuristic, by which, they judge the time saved based solely on the difference between the initial and higher speed.[7]
It seems that people falsely believe that journey time decreases somewhat linearly as driving speed increases, irrespective of the initial speed, causing the time-saving bias. Although it is still unclear what is the dominant heuristic people use to estimate time savings, it is evident that almost none follow the above curvilinear relationship.
Drivers who underestimated the time saved when increasing from a low speed or overestimated the time lost when decreasing from a high speed, overestimated the speed required for arriving on a specific time and chose unduly high speeds, sometimes even exceeding the stated speed limit.[2] Similarly, drivers who overestimated the time saved when increasing from a high speed underestimated the speed required for arriving on time and chose lower speeds.[8]
The time-saving bias is not limited to driving. The same faulty estimations emerge when people are asked to estimate savings in patients’ waiting time when adding more physicians to a health care center[9] or when estimating an increase in the productivity of a manufacturing line by adding more workers.[10]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Time-saving bias is a concept that describes people's tendency to misestimate the time that could be saved (or lost) when increasing (or decreasing) speed. In general, people underestimate the time that could be saved when increasing from a relatively low speed—e.g., 25 mph (40 km/h) or 40 mph (64 km/h)—and overestimate the time that could be saved when increasing from a relatively high speed—e.g., 55 mph (89 km/h) or 90 mph (140 km/h). People also underestimate the time that could be lost when decreasing from a low speed and overestimate the time that could be lost when decreasing from a high speed.
A paceometer is a measuring instrument that displays the time a journey over a given distance will take based on speed (for example, the number of minutes per 10 km). It serves as an alternative to the traditional speedometer and can be used to counteract time-saving bias, which is the human tendency to miscalculate the amount of time saved by increasing speed during an activity, such as driving or performing a task. Paceometers can discourage speeding by making it clear that increasing speed saves progressively less time when one is already driving fast. Journalist Rory Sutherland has described the paceometer as something that will "change the way you drive forever". Nassim Taleb has described the paceometer as mathematically trivial, yet completely counterintuitive. Increasing speed yields diminishing returns in terms of travel time. Simply put, at low speeds every kilometer per hour counts, whereas at high speeds one saves almost nothing—yet high speeds entail greater risks and costs.
Negative-bias temperature instability (NBTI) is a key reliability issue in MOSFETs, a type of transistor aging. NBTI manifests as an increase in the threshold voltage and consequent decrease in drain current and transconductance of a MOSFET. The degradation is often approximated by a power-law dependence on time. It is of immediate concern in p-channel MOS devices (pMOS), since they almost always operate with negative gate-to-source voltage; however, the very same mechanism also affects nMOS transistors when biased in the accumulation region, i.e. with a negative bias applied to the gate. More specifically, over time positive charges become trapped at the oxide-semiconductor boundary underneath the gate of a MOSFET. These positive charges partially cancel the negative gate voltage without contributing to conduction through the channel as electron holes in the semiconductor are supposed to. When the gate voltage is removed, the trapped charges dissipate over a time scale of milliseconds to hours. The problem has become more acute as transistors have shrunk, as there is less averaging of the effect over a large gate area. Thus, different transistors experience different amounts of NBTI, defeating standard circuit design techniques for tolerating manufacturing variability which depend on the close matching of adjacent transistors. NBTI has become significant for portable electronics because it interacts badly with two common power-saving techniques: reduced operating voltages and clock gating. With lower operating voltages, the NBTI-induced threshold voltage change is a larger fraction of the logic voltage and has a higher potential to disrupts operations. When a clock is gated off, transistors stop switching and NBTI effects accumulate much more rapidly. When the clock is re-enabled, the transistor thresholds have changed and the circuit may not operate. Some low-power designs switch to a low-frequency clock rather than stopping completely in order to mitigate NBTI effects. There is also a positive bias temperature instability (PBTI) which affects a nMOS transistor when positively biased. It has become more important with the introduction of high κ metal gates.
Length time bias (or length bias) is an overestimation of survival duration due to the relative excess of cases detected that are asymptomatically slowly progressing, while fast progressing cases are detected after giving symptoms. Length time bias is often discussed in the context of the benefits of cancer screening, and it can lead to the perception that screening leads to better outcomes when in reality it has no effect. Fast-growing tumors generally have a shorter asymptomatic phase than slower-growing tumors. Thus, there is a shorter period of time during which the cancer is present in the body (and so might be detected by screening) but not yet large enough to cause symptoms, that would cause the patient to seek medical care and be diagnosed without screening. As a result, if the same number of slow-growing and fast-growing tumors appear in a year, the screening test detects more slow-growers than fast-growers. If the slow growing tumors are less likely to be fatal than the fast growers, the people whose cancer is detected by screening do better, on average, than the people whose tumors are detected from symptoms (or at autopsy) even if there is no real benefit to catching the cancer earlier. That can give the impression that detecting cancers by screening causes cancers to be less dangerous even if less dangerous cancers are simply more likely to be detected by screening.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Joe Louis.
