mcmc simulation

Dear List,

I am reading a method and am unsure how to do something similar, so have come here for advice!

I have a observed value and a expected value generated from a null model.  I am looking to see if observed - expected is significantly different from zero.

So in the method in the paper it states: " .. significance of difference from zero was tested with Markov chain Monte Carlo simulation"

I have installed the package mcmc as this seemed a good place to start but i am unsure what function to call?

I have 600 data points in a data frame called diversity, where the observed value is called, well observed and the expected.. expected! 

Thanks for any advice.

Peter