proc genmod - cluster-level characteristics

[KPCklebspn]

Hi there - I have a dataset of individuals, where each individual is a close contact of an index case. So, individuals are clustered at the level of the index case. The outcome (infection) is yes/no - acquired infection from the index case.

Sample of dataset

IndexCase   contact    ContactCharacteristic     IndexCaseCharacteristic   infection

1                    1                    a                                    a                                     yes

1                    2                    b                                    a                                     yes 

1                    3                    c                                    a                                     no

2                    1                    a                                    b                                     no

2                    2                    b                                    b                                     no

Question is: what are risk factors for contacts acquiring infection for the index case? Risk of infection for contacts depends on contact characteristics and index case characteristics (i.e. individual-level and cluster-level characteristics).

Is the coding for this model correct? i.e. is it ok to put the cluster-level characteristic of interest (indexcharacteristic) in the model?

proc genmod data = dataset;
class indexcase;
model infection = ContactCharacteristic IndexCharacteristic/ dist=binomial link=logit;
repeated subject=indexcase / type = exch;

run;

Thanks!

[StatDave]

From your description, that seems like a reasonable model.