# Comparing two different counting methods: What test to use?

#### guppy

##### New Member
Hello there,

I counted sockeye salmon at a certain site using two different methods at coming up with the number of sockeye that passed by the site. For each day (41 days in total) I counted sockeye using two methods. One was counting the total number of sockeye over the hour and the other was only counting a sub-sampled portion of the hour then expanding for the remaining hour (i.e. 10 fish in 20 minutes so 30 fish in one hour). Some numbers are negative numbers (meaning that more fish went down than up). What statistical test can use to see if there is a significant different between the two methods and how can I perform it? Should I assume the counts are normally distributed or should I assume the opposite? Parametric or non-parametric?

Thanks in advance #### sasan

##### New Member
Hello there,

I counted sockeye salmon at a certain site using two different methods at coming up with the number of sockeye that passed by the site. For each day (41 days in total) I counted sockeye using two methods. One was counting the total number of sockeye over the hour and the other was only counting a sub-sampled portion of the hour then expanding for the remaining hour (i.e. 10 fish in 20 minutes so 30 fish in one hour). Some numbers are negative numbers (meaning that more fish went down than up). What statistical test can use to see if there is a significant different between the two methods and how can I perform it? Should I assume the counts are normally distributed or should I assume the opposite? Parametric or non-parametric?

Thanks in advance One option that you have is include both counting methods in your analysis using a Blocking ANOVA model. Each counting method is one block (then block have two level: counting method 1 and counting methods 2). If you have a block effect then you can exclude the method that agree with your criteria is less accurate.
Before to assume parametric data, you must to evaluate it, at least between groups variances homogeneous.

cheers, Mauro

#### guppy

##### New Member
Thanks Mauro,

However, I am not familiar with the blocking ANOVA. Can you link me to a website and/or some literature that explains how to set it up? I am still a bit of a novice with statistics.