[R] Fwd: high p values

[S Ellison]

> This is my function:
> 
> wilcox.test(A,B, data = data, paired = FALSE)
> 
> It gives me high p value, though the median of A column is 6900 and B
> column is 3500.
> 
> Why it gives p value high if there is a difference in the median?

Perhaps becuase a) because you are testing the wrong data or b) there isn't a significant difference 

a) You are probably not using the data you think you are. Check ?wilcox.test; the 'data' argument is specific to the formula method. That needs a formula as the first argument, not a numeric vector. What you've done is apply the default, and 'data' has been ignored. So A and B are whatever was lying around in your current environment, not what is in 'data'.  ('data' is a terrible name for a data frame, by the way, as 'data' is an R function). 

After that:
- How many data points do you have in each group?
- How much do the two groups overlap?

If the answers are 'not many' or 'lots' (in that order), and especially if both apply, you can't expect a significant test result.

S Ellison


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