{smcl}
{* 20 July 2005}{...}
{hline}
help for {hi:binscrn2} {right: (version 1.1.0) }
{hline}

{title:Comparison of binary screening tests - unpaired data}

{p 8 12}{cmd:binscrn2}
{it:result_var}
{it:disease_var}
{it:testtype_var}
{ifin}
[, {opt l:evel(#)}
{opt f:ormat(%fmt)}]


{title:Description}

{pstd}
{cmd:binscrn2} compares two screening tests with respect to true and false positive
rates, positive and negative predictive values, and diagnostic likelihood
ratios for binary test result data.

{pstd}
Positive and negative predictive values
assume cohort data; i.e. that the proportion of disease positive observations
in the dataset represents the population disease prevalence.

{pstd}
{it:testresult_var} is a 0/1 test result variable and {it:disease_var} is the
0/1 (disease) status indicator variable.  {it:testtype_var} identifies records corresponding to the
two test modalities to be compared.  Test result data are assumed to come from
two independent samples.

{pstd}relative screening measures and confidence limits are available as returned results after running the
program:

{col 8} rTPF:  r(rtpf)   [r(rtpf_lb), r(rtpf_ub) ]
{col 8} rFPF:  r(rfpf)   [r(rfpf_lb), r(rfpf_ub) ]
{col 8} rPPV:  r(rppv)   [r(rppv_lb), r(rppv_ub] ]
{col 8} rNPV:  r(rppv)   [r(rppv_lb), r(rppv_ub) ]
{col 8}rDLR+:  r(rdlrp)  [r(rdlrp_lb),r(rdlrp_ub)]
{col 8}rDLR-:  r(rdlrn)  [r(rdlrn_lb),r(rdlrn_ub)]

{pstd}along with the following joint rectangular confidence regions:

{col 8}joint rFPF,rTPF: r(fpfj_lb) r(fpfj_ub) x r(tpfj_lb) r(tpfj_ub)
{col 8}joint rNPV,rPPV: r(npvj_lb) r(npvj_ub) x r(ppvj_lb) r(ppvj_ub)

{pstd}and returned matrices for [ln(rDLR+),ln(rDLR-)] estimates and corresponding covariance matrix:

{col 8}  r(rDLR)          2x1
{col 8}  r(Cov_ln_rDLR)   2x2

{title:Options}

{phang}
{opt level(#)}; see {help estimation options##level():estimation options}.

{phang}
{opt format(%fmt)} specifies the display {help format} for estimates and CI's.  The
    default is %5.3g


{title:Remarks}

{pstd} Rectangular joint confidence regions (rFPF,rTPF) and (rNPV,rPPV) are based on
on sqrt(1-alpha) level Simel confidence limits (see References) for the component ratios
rFPF, rTPF, rNPV, rPPV.

{pstd} see {help binscrn1} to obtain various screening measures for results from a single
screening test with binary outcome and {help binscrn3} for comparison of tests
with paired data.


{title:References}

{pmore}Pepe MS.  {browse "http://www.fhcrc.org/science/labs/pepe/book":The Statistical Evaluation of Medical Tests for Classification and Prediction.}
Oxford University Press.  Chapter 3.  2003.
{break}

{pstd}calculation of confidence intervals for screening measure ratios per:

{pmore}Simel DL, Samsa GP, and Matchar DB.  Likelihood ratios with confidence: sample
size estimation for diagnostic test studies.  J. of Clin. Epidem. 44(8):763-70,
1991.


{title:Examples}

{phang} .use http://www.fhcrc.org/science/labs/pepe/book/data/hpns, clear {p_end}
{phang} .binscrn2 y d arm {p_end}
{phang} .binscrn2 y d arm, level(90) format(%6.2g){p_end}


{title:Author}

{pstd}Gary Longton, Fred Hutchinson Cancer Research Center, Seattle, WA.{break}
glongton@fhcrc.org