[R] Wilcox paired test error message

[Sarah Goslee]

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