# How to test Accuracy significantly different from chance?

#### ilaria

##### New Member
Hi All,

So I have more than 60 subjects who participated in an experiment.

I would like to exclude those who performed at chance level.
The problem is where should I set my cut off? Is 55% not chance? And 57?

So my prof said I should test if the suspect cases significantly differ from chance.
But how do I do that?

I would very much appreciate your help with that!!
Best
Ilaria

#### Karabiner

##### TS Contributor
Could you explain this a little bit? What is the research
topic, what is the research question, how was the experiment
designed, what was measured?

With kind regards

K.

#### ilaria

##### New Member
It's a delayed-match to sample task; So the subjs saw an item to remember and after a delay a different or identical item was presented and their task was to make a match ("this is the same item I saw before") vs no-match ("it's a different one") judgement;

The response is given by pressing one button for match and another for no-match. Half of the trials were match and half no-match. I measure accuracy (% of correct responses = hits + correct rejection ) and RTs. These are the details I can give , I hope it can help

Best
I.

#### Karabiner

##### TS Contributor
Take each participant as an experiment of his own,
with k trials. If you perform a binomial test, then
the Null hypothesis is that a particpant's rate of
correct responses is = 0.5 (chance level). The
question is, which rate of correct responses over
k trials will lead to rejection of the Null hypothesis.
You could use e.g. an online calculator for binomial
test to find this out.

With kind regards

K.