critical values

Terms from Statistics for HCI: Making Sense of Quantitative Data

In the days before computers, when all calculations were performed by hand, and even when computers were less powerful than they are today, you would check the significance level of a result by looking up the value in a table that listed the critical value of a given statistic for 5%, 1%, etc. For example, the critical value for the Student's t distribution with 10 degrees of freedom at a 5% significance level is 2.23. Suppose we performed a t test comparing the heights of 6 people from Cardiff and 6 from London (df = 6+6-2 = 10): if the t value were greater than this critical value of 2.23 we would conclude that London and Cardiff heights were different at the 5% significance level.

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