Examples

• Simple cross-wave comparisons:
  • crosstabulations of categorical variables
  • correlations of continuous variables
• For instance, change in vote intention between waves:

  get file 's:\bhps\spss\dindresp.sav'/keep=pid,dvote,asex.
  sort cases by pid.
  save out = 'c:\temp\tempd.sav'.
  get file 's:\bhps\spss\eindresp.sav'/keep=pid,evote,esex.
  sort cases by pid.
  
  match files file=*/file='c:\temp\tempd.sav'/by=pid.
  missing values all (-9 thru -1).
  recode dvote evote (4 thru 10=7).
  cro dvote by evote by dsex/cell = count row.
  

  Stata:

  use pid dvote dsex using s:\bhps\stata\dindresp
  sort pid
  save c:\temp\tempd,replace
  
  use pid evote esex using s:\bhps\stata\eindresp
  sort pid
  
  merge pid using c:\temp\tempd
  
  recode dvote -9/-1=. 4/10=7
  recode evote -9/-1=. 4/10=7
  
  bysort dsex: tab dvote evote, row
  

• Inspection of the table is interesting but we can go farther:
  • Calculate the proportion on and off the diagonal
  • Fit loglinear models

• We can fit a regression model relating income at one wave to characteristics at a prior wave (including income):
  
  $$y_t = \alpha + \beta \mathbf{x}_{t-1} + \gamma y_{t-1} + \epsilon$$
  
  

  missing values all (-9 thru -1).
  reg dep=bfimn /method=enter afimn ajbstat asex amastat.
  

• or
  
  $$y_t - y_{t-1} = \alpha + \beta \mathbf{x}_{t-1} + \epsilon$$
  
  

  compute delta = bfimn - afimn.
  reg dep=delta /method=enter ajbstat asex amastat.
  

  Stata:

  recode bfimn -9/-1=1
  recode ...
  xi: reg bfimn afimn i.ajbstat i.asex i.amastat
  

• or

  get delta = bfimn - afimn
  xi: reg delta i.ajbstat i.asex i.amastat
  

• For binary outcomes logistic regression on the same logic:

  compute bempl = any(bjbstat,1,2).
  logistic bempl /cat ajbstat asex aregion
    /method = enter ajbstat asex aregion afimn.
  

  Stata:

  gen bempl = inlist(bjbstat,1,2)
  xi: logit bempl i.ajbstat i.asex i.aregion afimn
  

• Those analyses are all based on specific pairs of waves.
• We may also want to look at all pairs of waves (i.e., all transitions) simultaneously
• For this we need the long format:

    ID   Wave Empstat          ID   Wave Empstat P-empstat
     1      1      1            1      1      1       .
     1      2      1  ------>   1      2      1       1
     1      3      4            1      3      4       1
     1      4      1            1      4      1       4
  

• An alternative way to generate the long format is to append files rather than match-merge them:

  add files file = 's:\bhps\spss\aindresp.sav' 
   /rename(ajbstat=emp) /in=w1
    /file = 's:\bhps\spss\bindresp.sav' 
   /rename(bjbstat=emp) /in=w2
    /file = 's:\bhps\spss\cindresp.sav' 
   /rename(cjbstat=emp) /in=w3
    /file = 's:\bhps\spss\dindresp.sav' 
   /rename(djbstat=emp) /in=w4
    /keep=pid,emp.
  
  if w1 wave=1.
  if w2 wave=2.        * Continued.../
  if w3 wave=3.
  if w4 wave=4.
  
  sort cases by pid,wave.
  
  if pid=lag(pid) pemp = lag(emp).
  exec.
  sel if not missing(pemp).
  missing values all (-9 thru -1).
  cro pemp by emp/cell = row count.
  

  Stata:

  use ajbstat asex using s:\bhps\stata\aindresp
  gen wave=1
  renpfix a
  save c:\temp\tempa,replace
  use bjbstat bsex using s:\bhps\stata\bindresp
  gen wave=2
  renpfix b
  save c:\temp\tempb,replace
  use cjbstat csex using s:\bhps\stata\cindresp
  gen wave=3
  renpfix c
  save c:\temp\tempc,replace
  use djbstat dsex using s:\bhps\stata\dindresp
  gen wave=4
  renpfix d
  save c:\temp\tempd,replace
  
  use c:\temp\tempa
  append using c:\temp\tempb
  append using c:\temp\tempc
  append using c:\temp\tempd
  
  sort pid wave
  
  by pid: gen pjbstat=jbstat[_n-1]
  

• This table pools all wave-on-wave transitions, but we can retrieve the wave specific ones thus:

  cro pemp by emp by wave/cell = row count.
  . . .
  temp.
  sel if wave=4.
  cro pemp by emp/cell = row count.
  

  Stata:

  tab pjbstat by jbstat if wave==4