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**   cs       **  Cohort study summaries
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  Overview:  The "cs" command is used to obtain summaries and inference
             for cohort or cross-sectional designs.  


  Usage:     "cs Dvar Evar"
             Where - Dvar is the disease variable (1=disease, 0=control)
                     Evar is the exposure variable (1=exposed, 0=unexposed)
             Note that the display for "cs" is with disease groups forming
             rows and exposure groups forming columns.

  Summaries: The "cs" command returns point estimates and confidence intervals
             for the risk difference, risk ratio, and (optionally) the odds
             ratio.  In addition, attributable or prevented fractions for
             the exposed and total population is returned.
 
             risk difference = p1 - p0, the difference between the probability
               of disease among the exposed minus the probability of disease
               among the unexposed.

             risk ratio = p1/p0,  the ratio of the probability
               of disease among the exposed relative to the probability 
               of disease among the unexposed.

             odds ratio = [p1/(1-p1)]/[p0/(1-p0)], the ratio of the odds
               of disease among the exposed relative to the odds 
               of disease among the unexposed.

             attributable fraction for the exposed = the percent of cases
               among the exposed that could be eliminated if exposure was
               eliminated.  Computed as (p1-p0)/p1 = [RR-1]/RR.

             attributable fraction for population = the percent of cases
               within the population that could be eliminated if exposure was
               eliminated.  Let N1 be the number of exposed, and N0 be the
               number of unexposed.  We would remove N1*(p1-p0)/p1 cases by
               removing exposure.  The fraction of total cases would be this
               amount relative to the total number of cases, N1+N0.  Therefore,
               the net effect in the population is [N1*(p1-p0)/p1]/(N1+N0) =
               (percent exposed among cases)*(attr fraction exposed).


  Options:   (1) "cs Dvar Evar [fweight=freq]"  -- this is used when the 
                 data are in a "grouped" format with the number of 
                 cases/controls that have a certain covariate combination 
                 given by the variable "freq".  See notes pg 52 for cc example.

             (2) "cs Dvar Evar, exact"  -- the exact option will compute
                  significance using Fisher's exact test.

             (3) "cs Dvar Evar, by(Svar)"  -- specifies that 2x2 tables
                  are to be formed for the strata given by "Svar".  Within
                  stratum statistics are shown and then combined with
                  Mantel-Haenszel weights.

             (4) "cc Dvar Evar, by(Svar) bd" -- the addition of "bd" 
                  specifies that the Breslow-Day test of homogeneity of
                  risk ratios across the strata be calculated.



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**   cc       **  Case-control summaries
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  Overview:  The "cc" command is used to obtain summaries and inference
             for case-control or cross-sectional designs.  


  Summaries: The "cc" command returns point estimates and confidence intervals
             for the the odds ratio and attributable or prevented fractions for
             the exposed and total population.


  Usage:     "cc Dvar Evar"
             Where - Dvar is the disease variable (1=disease, 0=control)
                     Evar is the exposure variable (1=exposed, 0=unexposed)
             Note that the display for "cc" is with disease groups forming
             rows and exposure groups forming columns.


  Options:   (1) "cc Dvar Evar [fweight=freq]"  -- this is used when the 
                 data are in a "grouped" format with the number of 
                 cases/controls that have a certain covariate combination 
                 given by the variable "freq".  See notes pg 52.

             (2) "cc Dvar Evar, exact"  -- the exact option will compute
                  significance using Fisher's exact test.

             (3) "cc Dvar Evar, by(Svar)"  -- specifies that 2x2 tables
                  are to be formed for the strata given by "Svar".  Within
                  stratum statistics are shown and then combined with
                  Mantel-Haenszel weights.

             (4) "cc Dvar Evar, by(Svar) bd" -- the addition of "bd" 
                  specifies that the Breslow-Day test of homogeneity of
                  odds ratios across the strata be calculated.


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**   mcc      **  Matched case-control summaries
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  Overview:  The "mcc" command is used to obtain summaries and inference
             for matched case-control or cross-sectional designs.  


  Summaries: The "mcc" command returns McNemar's chi-square test, point 
             estimates and confidence intervals for the difference, ratio,
             and relative difference of the proportion with the exposure,
             along with the odds ratio.


  Usage:     "mcc Evar1 Evar0"
             Where - Evar1 is the exposure variable (1=exposed, 0=unexposed)
                       for the cases.
                     Evar0 is the exposure variable (1=exposed, 0=unexposed)
                       for the controls.


  Options:   (1) "mcc Evar1 Evar0 [fweight=freq]"  -- this is used when the 
                 data are in a "grouped" format with the number of 
                 cases/controls that have a certain covariate combination 
                 given by the variable "freq".  See notes pg 52.

             (2) Note:  there is no exact option since the default ouput 
                 also calculates exact binomial p-values.

             (3) Note:  the by(Svar) option is not available.  To obtain 
                 separate analyses one need to use
                 "mcc Evar1 Evar0 if Svar==1"