Dear all,
I need to run a CACE analysis and I found some online references suggesting this can be done in Stata using the -ivregress- command. I am analysing data from a RCT and I found an effect of intervention arm on the main outcome as part of my ITT analysis; however, it has been suggested I should now use a causal model approach with instrumental variables to be able to compare the compliers in the intervention group with the 'compliers' in the control group, had they been offered the intervention.
Compliance is defined as attending all sessions. I have identified predictors of compliance in the study arm and used these predictors to identify the 'compliers' in the control group. Now I can use -ivregress- as follows:
xi: ivregress 2sls fSFpro bSFpro i.centre (comply=arm)
BUT the results are unreasonable as the coefficient of 'comply' on the outcome is very large (my scale only ranges from 0-33 on a continuous) - attached doc - the b = 537 and 95%CI: -4934 to 6008.
I would welcome any suggestion on what could be going on and wrong and ways to rectify it.
Many thanks in advance,
Francesca
table.docx
I need to run a CACE analysis and I found some online references suggesting this can be done in Stata using the -ivregress- command. I am analysing data from a RCT and I found an effect of intervention arm on the main outcome as part of my ITT analysis; however, it has been suggested I should now use a causal model approach with instrumental variables to be able to compare the compliers in the intervention group with the 'compliers' in the control group, had they been offered the intervention.
Compliance is defined as attending all sessions. I have identified predictors of compliance in the study arm and used these predictors to identify the 'compliers' in the control group. Now I can use -ivregress- as follows:
xi: ivregress 2sls fSFpro bSFpro i.centre (comply=arm)
BUT the results are unreasonable as the coefficient of 'comply' on the outcome is very large (my scale only ranges from 0-33 on a continuous) - attached doc - the b = 537 and 95%CI: -4934 to 6008.
I would welcome any suggestion on what could be going on and wrong and ways to rectify it.
Many thanks in advance,
Francesca
table.docx
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