Tuesday, January 22, 2013

Is our food shrinking? | Life and style | The Guardian

Is our food shrinking? | Life and style | The Guardian

Brands that don't want their customers to see shrinking products as a price hike live by Weber's law, says Mitchell. This is the idea that if you present people with a stimulus of a varying intensity – and the change is small enough – they won't notice it. To notice the change, the variation has to have exceeded what is known as the "just noticeable difference" (JND).
"This," the City University academic says, "is fairly consistent – around about 10%. So, for example, if you reduce the number of crisps by 10% people tend not to notice – you get away with i
(from the page on Weber's law : http://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_3/ch3p1.html)

E. H. Weber, in 1834, had the following insight:

The number in this example are made up; your values may vary in practice.

If you lift up and hold a weight of 2.0 kg, you will notice that it takes some effort. If you add to this weight another 0.05 kg and lift, you may not notice any difference between the apparent or subjective weight between the 2.0 kg and the 2.1 kg weights. If you keep adding weight, you may find that you will only notice the difference when the additional weight is equal to 0.2 kg. The increment threshold for detecting the difference from a 2.0 kg weight is 0.2 kg. The just noticeable difference (jnd) is 0.2 kg.

Now start with a 5.0 kg weight. If you add weight to this, you will find that the just noticeable difference is 0.5 kg. It takes 0.5 kg added to the 5.0 kg weight for you to notice an apparent difference.

The ratio of I/I for both instances (0.2/2.0 = 0.5/5.0 = 0.1) is the same. This is Weber's Law.

Weber's Law states that the ratio of the increment threshold to the background intensity is a constant. So when you are in a noisy environment you must shout to be heard while a whisper works in a quiet room. And when you measure increment thresholds on various intensity backgrounds, the thresholds increase in proportion to the background.

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