Difference between revisions of "Null Hypothesis"
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| − | + | In his 1935 book The Design of Experiments, Fisher described how to test such a claim. Instead of trying to prove that Bristol could tell the difference between the cups of tea, he would try to reject the hypothesis that her choices were random. “We may speak of this hypothesis as the ‘null hypothesis,’ ” Fisher wrote. “The null hypothesis is never proved or established, but is possibly disproved, in the course of experimentation. Every experiment may be said to exist only in order to give the facts a chance of disproving the null hypothesis.” | |
Fisher sketched out a way to reject the null hypothesis—that Bristol’s choices were random. He would prepare eight cups, putting milk first into four of them, and milk second into the other four. He would scramble the cups into a random order and offer them to Bristol to sip, one at a time. She would then divide them into two groups—the cups that she believed had received milk first would go in one group, milk second in the other. | Fisher sketched out a way to reject the null hypothesis—that Bristol’s choices were random. He would prepare eight cups, putting milk first into four of them, and milk second into the other four. He would scramble the cups into a random order and offer them to Bristol to sip, one at a time. She would then divide them into two groups—the cups that she believed had received milk first would go in one group, milk second in the other. | ||
Revision as of 21:00, 7 August 2014
In his 1935 book The Design of Experiments, Fisher described how to test such a claim. Instead of trying to prove that Bristol could tell the difference between the cups of tea, he would try to reject the hypothesis that her choices were random. “We may speak of this hypothesis as the ‘null hypothesis,’ ” Fisher wrote. “The null hypothesis is never proved or established, but is possibly disproved, in the course of experimentation. Every experiment may be said to exist only in order to give the facts a chance of disproving the null hypothesis.”
Fisher sketched out a way to reject the null hypothesis—that Bristol’s choices were random. He would prepare eight cups, putting milk first into four of them, and milk second into the other four. He would scramble the cups into a random order and offer them to Bristol to sip, one at a time. She would then divide them into two groups—the cups that she believed had received milk first would go in one group, milk second in the other.
Bristol reportedly passed the test with flying colors, correctly identifying all eight cups. Thanks to the design of Fisher’s experiment, the odds that she would divide eight cups into two groups correctly by chance were small. There were 70 different possible ways to divide eight cups into two groups of four, which meant that Bristol could identify the cups correctly by chance only once out of every 70 trials.
Fisher’s test couldn’t completely eliminate the possibility that Bristol was guessing. It just meant that the chance she was guessing was low. He could have reduced the odds further by having Bristol drink more tea, but he could never reduce the chances she was guessing to zero.
