[R] Wilcox paired test error message
Sarah Goslee
sarah.goslee at gmail.com
Mon Jun 24 15:21:59 CEST 2013
G'morning.
On Mon, Jun 24, 2013 at 2:22 AM, peter dalgaard <pdalgd at gmail.com> wrote:
>
> On Jun 23, 2013, at 22:30 , Sarah Goslee wrote:
>
>> Hi,
>>
>> If you're doing exactly as described below, then you need to add the
>> data argument to wilcox.test so R knows where to find beforesmall and
>> aftersmall. But if so, that's a rather uninformative error message.
>>
>> Saraj
>
> Not really, if you use the formula interface, the rhs is supposed to be the grouping, as in
>
> wilcox.test(extra ~ group, data=sleep, paired=TRUE)
>
> so it's telling you that "aftersmall" does not describe two groups.
Yep, sorry. That was actually my first thought, but then I misread the
helpfile.
You do still need the data argument, though. :)
Sarah
> (It is unfortunate, though, that we don't have a formula interface to the parallel-vector data layout for paired tests. That is the common case, the sleep data set is a rather rare exception. A formula specification for paired columns has been talked about; something like cbind(before, after) ~ 1 should be workable, but nothing has materialized to date.)
>
> -pd
>
>>
>> On Sun, Jun 23, 2013 at 2:34 PM, ruth parker <parkeractonruth at gmail.com> wrote:
>>> Hi,
>>> I've been trying to run a wilcox paired test on some data
>>> beforesmall aftersmall
>>> [1,] 63.5 512.0
>>> [2,] 54.5 237.5
>>> [3,] 52.5 161.5
>>> [4,] 78.0 153.5
>>> [5,] 53.5 68.0
>>> [6,] 50.5 65.5
>>> [7,] 69.0 52.0
>>> [8,] 76.0 59.0
>>> [9,] 68.0 66.5
>>> [10,] 75.5 66.5
>>> [11,] 67.0 45.5
>>> [12,] 81.0 54.5
>>> [13,] 49.0 44.0
>>> [14,] 51.0 42.5
>>> [15,] 53.0 34.5
>>>
>>> using
>>> wilcox.test(beforesmall ~ aftersmall,paired=T)
>>> but I get the error message:
>>>
>>> Error in wilcox.test.formula(beforesmall ~ aftersmall, paired = T) :
>>> grouping factor must have exactly 2 levels
>>>
>>> I don't have any missing values, I have the same amount of data points for
>>> each group and I've looked everywhere trying to find the answer.
>>> Please can somebody tell me how to make it work
>>> thanks
>>>
>>
--
Sarah Goslee
http://www.functionaldiversity.org
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