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Stuck on probability sample solution, can you help

uvox · 2011-11-28 23:58:49

Would appreciate if someone can solve/tell me how to solve this. The most common formula for determining sample sizes in investigating usability problems is 1-(1-L)n -where n is the power of. L is the proportion of an error found in a usability test by a single user. In this case it is .77. n gives number of users in the…

28-11-2011 11:58pm

#1

uvox

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Would appreciate if someone can solve/tell me how to solve this.

The most common formula for determining sample sizes in investigating usability
problems is 1-(1-L)n -where n is the power of.

L is the proportion of an error found in a usability test by a single user. In this case it is .77.

n gives number of users in the sample I would need before I hit that error.

I want to set a probablility of that error happening as 90%. That gives .90 = 1- (1-.77)n

How do I solve for n?

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Comments

#2 29-11-2011 12:05am

ray giraffe

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(0.23)^n = 0.1

Now try to solve using logs. Good explanation of logs here.

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