********************************************************************
* File			    HALCyon body size syntax_BoydOrr.do
* BY				Rebecca Hardy, MRC Unit for Lifelong Health and Ageing at UCL
* FOR				HALCyon cross-cohort collaboration (funded by the New Dynamics of Ageing (RES-353-25-0001))
* DATASET			Boyd Orr cohort study
* Date Created 		12/05/2010
* last modified	    15/07/2010

* PURPOSE			Recodes and derives body size variables for use in cross-cohort analyses
*************************************************************************************


# delimit;
set more off;


/*BMI and height at wave 3*/
gen bmi_w3=b3bmi_combined ;
label variable bmi_w3 "Body mass index (kg/m2) at wave 3" ;
gen ht_w3=b3height_combined/10 ;
label variable ht_w3 "Height (cm) at wave 3" ;


/*birth weight*/
gen bwtkg=b2birthweight_combined ;
label variable bwtkg "Birth weight (kg)" ;

/*recalled height and weight at 20 years*/
mvdecode heightfeet heightinches height20feet height20inches weightstones weightpounds var1 var2 var3 var4, mv(99) ;

gen ht20=(height20feet*12)+height20inches ;
gen ht20cm=ht20*2.54 ;
label variable ht20cm "Height at age 20 years (cm)" ; 
gen wt20=(var1*14)+var2 ;
gen wt20kg=wt20*0.454 ;
label variable wt20kg "Weight at age 20 years (kg)" ; 
gen bmi20=wt20kg/((ht20cm/100)^2) ;
label variable bmi20 "BMI at age 20 years (kg/m2)" ; 

/*recalled height and weight at 40 years*/
by sex, sort: summ var3 var4, d ;
gen wt40=(var3*14)+var4 ;
gen wt40kg=wt40*0.454 ;
label variable wt40kg "Weight at age 40 years (kg)" ; 
gen bmi40=wt40kg/((ht20cm/100)^2) ;
label variable bmi40 "BMI at age 40 years (kg/m2)" ; 

/*body size at wave 2*/
mvdecode heightfeet heightinches, mv(99) ;
by sex, sort: summ b2height_self b2bmi_self heightfeet heightinches, d ;

gen b2heightcm=b2height_self/10 ;

gen height_check=((heightfeet*12)+heightinches)*2.54 ;
gen weight_check=((weightstones*14)+weightpounds)*0.454 ;
gen BMI_check=(weight_check)/((height_check/100)^2) ;

gen b2weight=(b2bmi_self)*((b2heightcm/100)^2)  ;

/*compute z-scores*/
egen bmi20m=std(bmi20) if sex==1 ;
egen bmi20f=std(bmi20) if sex==2 ;

gen bmi20z=. ;
replace bmi20z=bmi20m if sex==1 ; 
replace bmi20z=bmi20f if sex==2 ; 

egen bmi40m=std(bmi40) if sex==1 ;
egen bmi40f=std(bmi40) if sex==2 ;

gen bmi40z=. ;
replace bmi40z=bmi40m if sex==1 ; 
replace bmi40z=bmi40f if sex==2 ;

egen bmi_w2m=std(b2bmi_self) if sex==1 ;
egen bmi_w2f=std(b2bmi_self) if sex==2 ;

gen bmi_w2z=. ;
replace bmi_w2z=bmi_w2m if sex==1 ; 
replace bmi_w2z=bmi_w2f if sex==2 ; 

/*compute velocities*/
gen bmi2040=(bmi40-bmi20)/20 ;

egen bmi2040m=std(bmi2040) if sex==1 ;
egen bmi2040f=std(bmi2040) if sex==2 ;

gen bmi2040z=. ;
replace bmi2040z=bmi2040m if sex==1 ; 
replace bmi2040z=bmi2040f if sex==2 ;

gen bmi40c=(bmi_w3-bmi40)/(age_w3-40) ;

egen bmi40cm=std(bmi40c) if sex==1 ;
egen bmi40cf=std(bmi40c) if sex==2 ;

gen bmi40cz=. ;
replace bmi40cz=bmi40cm if sex==1 ; 
replace bmi40cz=bmi40cf if sex==2 ;

/*wave 2 approximately five years prior to wave 3*/

gen bmi40w2=(b2bmi_self-bmi40)/((age_w3-5)-40) ;

egen bmi40w2m=std(bmi40w2) if sex==1 ;
egen bmi40w2f=std(bmi40w2) if sex==2 ;

gen bmi40w2z=. ;
replace bmi40w2z=bmi40w2m if sex==1 ; 
replace bmi40w2z=bmi40w2f if sex==2 ;

gen bmiw2c=(bmi_w3-b2bmi_self)/5 ;

egen bmiw2cm=std(bmiw2c) if sex==1 ;
egen bmiw2cf=std(bmiw2c) if sex==2 ;

gen bmiw2cz=. ;
replace bmiw2cz=bmiw2cm if sex==1 ; 
replace bmiw2cz=bmiw2cf if sex==2 ;