Another option is to use something like RUVseq to estimate factors of hidden variation. Maybe this captures a combination of age, sex and other unwanted confounders in one or a few factors so you can adjust for this rather than sex, age individually. With human data it is likely that you have many confounders that you cannot explain by the metadata, for example genetic predisposition, drug intake, overall health status, diet, lifestyle etc.
How to solve DESeq2 Error in checkFullRank(modelMatrix) cause by biological replicates information?
I have 4 factors in the design formula in DESeq2
dds <- DESeqDataSetFromMatrix(countData = dfinput0,
colData = sampleTable,
design= ~ condition+age+sex+type,condition:type )
I got the error:
Error in checkFullRank(modelMatrix) :
the model matrix is not full rank, so the model cannot be fit as specified.
One or more variables or interaction terms in the design formula are linear
combinations of the others and must be removed.
This is my coldata:
condition type age sex
1 control z 57 Female
2 control af 72 Male
3 control ac 22 Male
4 control ab 71 Female
5 control ab 71 Female
6 control at 68 Male
7 control ba 81 Male
8 control ba 81 Male
9 control bh 68 Male
10 control bh 68 Male
11 control am 81 Male
12 control am 81 Male
13 control an 79 Male
14 control ao 83 Female
15 control ap 71 Male
16 control ap 71 Male
17 control aq 77 Male
18 control aq 77 Male
19 control ar 59 Male
20 control as 67 Female
21 control au 80 Female
22 control au 80 Female
23 control av 77 Female
100 treated e 48 Male
101 treated e 48 Male
102 treated e 48 Male
103 treated b 32 Female
104 treated b 32 Female
105 treated f 45 Female
106 treated f 45 Female
107 treated a 68 Male
108 treated a 68 Male
109 treated j 64 Male
110 treated j 64 Male
111 treated i 69 Male
112 treated i 69 Male
113 treated h 45 Female
114 treated c 59 Male
115 treated c 59 Male
116 treated g 75 Female
117 treated g 75 Female
the type column which represent biological replicates within the condition cause this error. Each sample is coming from human samples and for some human samples there are 2 or 3 sample, for others there is only one sample per human. How can I include the biological replicate information without having this error to DESEq2 analysis?
3 answers
You can't, as they are not split between your condition of interest. You need them present in both groups to account for them properly. age is also going to be a problem, as it's assuming a linear increase in expression with time.
My advice would be to remove those terms from your design and look at the resulting PCA to see if they're actually confounding factors or not. Nothing you can do for type, but you could consider create age bins that would be usable in your design. Currently, sex is the only thing that can be accounted for properly and simply.
Here's a similar question with some responses from the DESeq2 dev.
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jared.andrews07
Yeah, RUVseq has its own caveats, but may be worth a shot. I'd prefer to see some indications that there is unwanted variation first before trying it though.
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jared.andrews07
...fine, I guess. But I'd still prefer to see that such variation is obfuscating the variable of interest before complicating the model.
In particular because it's not clear how to set k for RUVseq, and I have yet to see the authors provide much guidance beyond "try a few and see which looks best", which feels bad. And in my experience, it changes things in a significant way downstream. I guess I am just conservative when it comes to model design and would rather sacrifice sensitivity for precision.
In short, if it doesn't seem like a problem, why try to address it? The RUVseq devs seem to also recommend this philosophy.
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jared.andrews07
I actaully don't think that age will be a problem, if treated as a continuous covariate, rather than a factor. However (as Mike notes in the linked thread), that would assume there was a log-linear relationship between age and expression, which is unlikely to be precisely true.
However, I do think that the problem with age is soluble, where as the problem with type is far more difficult structural problem.
The problem here is that DESeq2 can only deal with replication at one level, where as you have replication at multiple levels - you have multiple patients, each with multiple replicates. Traditional statistical practice here would be to use a mixed effects model, with the patient as a fixed effect and the replicates within the patient as a random effect.
You can't do this with DESeq2, so you have two/three options.
You could use DESeq2, but choose to only be interested in one of the levels of variation - You could assume there is a "true" level of expression in each patient, of which each sample is a noisey estimate (that is, in the perfect experiment, each replicate from the same patient would be identical), and model the variation between patients - this would involve collapsing the within patient replicates, by summing the counts (this is what limma's collapseReplicates). Or you could assume that there is a "true" level of expression for the condition, of which each patient is a noisy estimate of, but that thing truly vary over time/location within a patient. In this case, you would treat each sample as independent and ignore the patient effect.
Or you could use something other than DESeq2. limma has a duplicateCorrelation function, which, as I understand it, produces results similar to a mixed effects model. It was originally designed to deal with microarrays that have multiple probes for the same gene, but has since been re-purposed to deal with this sort of intra-subject variability.
There is also dream in the variancePartition package, which is more or less a drop-in replacement for limma that uses a linear mixed model. That vignette also has an example of using limma's duplicateCorrelation and compares/comments on the two approaches.
I have not used it (and my grasp of modeling is poor in general), but it seems like it'd be worth a look as well.
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jared.andrews07
As nice as it would be to be able to account for all those things, if all those things really do affect your end results significantly, you would have to have done a much more massive experiment in order to properly model that. You can't have one type z sample of one age and one treatment and expect to be able to model what that means across all the ages and treatments.
It's great that you kept all that metadata, but you realistically aren't going to be able to use it all. Use PCA to figure out what matters, and dump the metadata elements that don't correspond with the first few PCs. Type is almost certainly going to have to go, unless you have a lot more samples than you are showing here, and have multiple samples for each type for control and treatment.
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You'll want to use the
collapseReplicates()function in DESeq2, see https://rdrr.io/bioc/DESeq2/man/collapseReplicates.html.That function is only intended for technical replicates, which is not the case here.