* Load the WISH Total Fat Data
* The web site has the Stata data set

* Do a naive regression of the FFQ total fat (log scale) 
* on age, bmi and the mean of the 6 24hr recalls (log scale)
regress lffq age bmi lfrmean

* Do regression calibration, assuming that the measurement 
* errors in the 24hr recalls are independent
rcal (lffq = age bmi) (w3: lfr1 lfr2 lfr3 lfr4 lfr5 lfr6)

* Use the mean of the 6 diaries (log scale) as an 
* instrumental variable, to check whether independence 
* of the measurement error
* in the 24hr recalls is reasonable
qvf lffq age bmi lfrmean (age bmi lfdmean)