Is it significantly different from chance?

Can someone give me a second opinion on this, or suggest some alternative test I might want to use?

I've run an experiment with 5 trials. Each trial has 1 correct answer and 4 incorrect answers.

I'd like to see if the average number of correct trials is significantly different from chance. The average score is 3.9.

Seems to me I could use the Binomial probability distribution formula (I've set superscripts in red):

P(Y = y) =

where p, the probability of success = 20%
n, the number of identical trials = 5
q = 1-p (80%)
Y, the number of successes in n trials = 3.9 (average number of correct trials)

Thoughts? Opinions?

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