{smcl}
{* *! version 1.1.12  20jun2011}{...}
{cmd:help ztp}{right:dialogs:  {dialog ztp}  {dialog ztp, message(-svy-) name(svy_ztp):svy: ztp}{space 8}}
{right:also see:  {help ztp postestimation}{space 3}}
{right:{help prdocumented:previously documented}}
{hline}
{pstd}
{cmd:ztp} has been superseded by {helpb tpoisson}.  {cmd:tpoisson} allows the
specification of any nonnegative integer as the left truncation point; thus
it does what {cmd:ztp} can do and more. 
{cmd:ztp} continues to work but, as of Stata 12, is no longer an official
part of Stata.  This is the original help file, which we will no longer
update, so some links may no longer work.


{title:Title}

{p2colset 5 16 18 2}{...}
{p2col :{bf:[R] ztp} {hline 2}}Zero-truncated Poisson regression{p_end}
{p2colreset}{...}


{title:Syntax}

{p 8 16 2}
{cmd:ztp} {depvar} [{indepvars}] {ifin} {weight} [{cmd:,}
{it:options}] 

{synoptset 26 tabbed}{...}
{synopthdr:options}
{synoptline}
{syntab:Model}
{synopt :{opt nocon:stant}}suppress constant term{p_end}
{synopt :{opth e:xposure(varname:varname_e)}}include ln({it:varname_e}) in model with coefficient constrained to 1{p_end}
{synopt :{opth off:set(varname:varname_o)}}include {it:varname_o} in model with coefficient constrained to 1{p_end}
{synopt :{cmdab:const:raints(}{it:{help estimation options##constraints():constraints}}{cmd:)}}apply specified linear constraints{p_end}
{synopt:{opt col:linear}}keep collinear variables{p_end}

{syntab:SE/Robust}
{synopt :{opth vce(vcetype)}}{it:vcetype} may be {opt oim},
   {opt r:obust}, {opt cl:uster} {it:clustvar}, {opt opg}, {opt boot:strap},
  or {opt jack:knife}{p_end}

{syntab:Reporting}
{synopt :{opt l:evel(#)}}set confidence level; default is
{cmd:level(95)}{p_end}
{synopt :{opt ir:r}}report incidence-rate ratios{p_end}
{synopt :{opt nocnsr:eport}}do not display constraints{p_end}
{synopt :{it:{help ztp##display_options:display_options}}}control spacing
           and display of omitted variables and base and empty cells{p_end}

{syntab:Maximization}
{synopt :{it:{help ztp##maximize_options:maximize_options}}}control the maximization process; seldom used{p_end}

INCLUDE help shortdes-coeflegend
{synoptline}
{p2colreset}{...}
INCLUDE help fvvarlist
{p 4 6 2}{it:depvar} and {it:indepvars} may contain time-series operators; see {help tsvarlist}.{p_end}
{p 4 6 2}{opt bootstrap}, {opt by}, {opt jackknife}, {opt rolling},
{opt statsby}, and {opt svy} are allowed; see {help prefix}.{p_end}
{p 4 6 2}Weights are not allowed with the {helpb bootstrap} prefix.{p_end}
{p 4 6 2}
{opt vce()} and weights are not allowed with the {helpb svy} prefix.
{p_end}
{p 4 6 2}{opt fweight}s, {opt iweight}s, and {opt pweight}s are allowed; see
{help weight}.{p_end}
{p 4 6 2}
{opt coeflegend} does not appear in the dialog box.{p_end}
{p 4 6 2}See {manhelp ztp_postestimation R:ztp postestimation} for features
available after estimation.{p_end}


{title:Menu}

{phang}
{bf:Statistics > Count outcomes > Zero-truncated Poisson regression}


{title:Description}

{pstd}
{cmd:ztp} fits a zero-truncated Poisson (ZTP) maximum-likelihood regression of
{depvar} on {indepvars}, where {it:depvar} is a positive count variable.


{title:Options}

{dlgtab:Model}

{phang}
{opt noconstant}, {opth exposure:(varname:varname_e)}, {opt offset(varname_o)}, 
{opt constraints(constraints)}, {opt collinear}; see
{helpb estimation options:[R] estimation options}.

{dlgtab:SE/Robust}

INCLUDE help vce_asymptall

{dlgtab:Reporting}

{phang}
{opt level(#)}; see {helpb estimation options##level():[R] estimation options}.

{phang}
{opt irr} reports estimated coefficients transformed to incidence-rate
ratios, that is, exp(b) rather than b.  Standard errors and confidence
intervals are similarly transformed.  This option affects how results are
displayed, not how they are estimated.  {opt irr} may be specified at
estimation or when replaying previously estimated results.

{phang}
{opt nocnsreport}; see
     {helpb estimation options##nocnsreport:[R] estimation options}.

{marker display_options}{...}
{phang}
{it:display_options}:
{opt noomit:ted},
{opt vsquish},
{opt noempty:cells},
{opt base:levels},
{opt allbase:levels};
   see {helpb estimation options##display_options:[R] estimation options}.

{marker maximize_options}{...}
{dlgtab:Maximization}

{phang}
{it:maximize_options}:
{opt dif:ficult}, {opt tech:nique(algorithm_spec)},
{opt iter:ate(#)}, [{cmd:{ul:no}}]{opt lo:g}, {opt tr:ace}, 
{opt grad:ient}, {opt showstep},
{opt hess:ian},
{opt showtol:erance},
{opt tol:erance(#)},
{opt ltol:erance(#)}, {opt nrtol:erance(#)},
{opt nonrtol:erance}, and
{opt from(init_specs)}; see {manhelp maximize R}.  These options are seldom
used.

{pmore}
Setting the optimization type to {cmd:technique(bhhh)} resets the default
{it:vcetype} to {cmd:vce(opg)}.

{pstd}
The following option is available with {opt ztp} but is not shown in the
dialog box:

{phang}
{opt coeflegend}; see
     {helpb estimation options##coeflegend:[R] estimation options}.


{title:Examples}

{phang}{cmd:. webuse runshoes}{p_end}
{phang}{cmd:. ztp shoes distance male age}{p_end}
{phang}{cmd:. ztp shoes distance male, exposure(age)}{p_end}


{title:Saved results}

{pstd}
{cmd:ztp} saves the following in {cmd:e()}:

{synoptset 20 tabbed}{...}
{p2col 5 20 24 2: Scalars}{p_end}
{synopt:{cmd:e(N)}}number of observations{p_end}
{synopt:{cmd:e(k)}}number of parameters{p_end}
{synopt:{cmd:e(k_eq)}}number of equations{p_end}
{synopt:{cmd:e(k_eq_model)}}number of equations in model Wald test{p_end}
{synopt:{cmd:e(k_dv)}}number of dependent variables{p_end}
{synopt:{cmd:e(k_autoCns)}}number of base, empty, and omitted constraints{p_end}
{synopt:{cmd:e(df_m)}}model degrees of freedom{p_end}
{synopt:{cmd:e(r2_p)}}pseudo-R-squared{p_end}
{synopt:{cmd:e(ll)}}log likelihood{p_end}
{synopt:{cmd:e(ll_0)}}log likelihood, constant-only model{p_end}
{synopt:{cmd:e(N_clust)}}number of clusters{p_end}
{synopt:{cmd:e(chi2)}}chi-squared{p_end}
{synopt:{cmd:e(p)}}significance{p_end}
{synopt:{cmd:e(rank)}}rank of {cmd:e(V)}{p_end}
{synopt:{cmd:e(ic)}}number of iterations{p_end}
{synopt:{cmd:e(rc)}}return code{p_end}
{synopt:{cmd:e(converged)}}{cmd:1} if converged, {cmd:0} otherwise{p_end}

{synoptset 20 tabbed}{...}
{p2col 5 20 24 2: Macros}{p_end}
{synopt:{cmd:e(cmd)}}{cmd:ztp}{p_end}
{synopt:{cmd:e(cmdline)}}command as typed{p_end}
{synopt:{cmd:e(depvar)}}name of dependent variable{p_end}
{synopt:{cmd:e(wtype)}}weight type{p_end}
{synopt:{cmd:e(wexp)}}weight expression{p_end}
{synopt:{cmd:e(title)}}title in estimation output{p_end}
{synopt:{cmd:e(clustvar)}}name of cluster variable{p_end}
{synopt:{cmd:e(offset)}}offset{p_end}
{synopt:{cmd:e(chi2type)}}{cmd:Wald} or {cmd:LR}; type of model chi-squared
	test{p_end}
{synopt:{cmd:e(vce)}}{it:vcetype} specified in {cmd:vce()}{p_end}
{synopt:{cmd:e(vcetype)}}title used to label Std. Err.{p_end}
{synopt:{cmd:e(opt)}}type of optimization{p_end}
{synopt:{cmd:e(which)}}{cmd:max} or {cmd:min}; whether optimizer is to perform
                         maximization or minimization{p_end}
{synopt:{cmd:e(ml_method)}}type of {cmd:ml} method{p_end}
{synopt:{cmd:e(user)}}name of likelihood-evaluator program{p_end}
{synopt:{cmd:e(technique)}}maximization technique{p_end}
{synopt:{cmd:e(singularHmethod)}}{cmd:m-marquardt} or {cmd:hybrid}; method used
                          when Hessian is singular{p_end}
{synopt:{cmd:e(crittype)}}optimization criterion{p_end}
{synopt:{cmd:e(properties)}}{cmd:b V}{p_end}
{synopt:{cmd:e(predict)}}program used to implement {cmd:predict}{p_end}
{synopt:{cmd:e(asbalanced)}}factor variables {cmd:fvset} as {cmd:asbalanced}{p_end}
{synopt:{cmd:e(asobserved)}}factor variables {cmd:fvset} as {cmd:asobserved}{p_end}

{synoptset 20 tabbed}{...}
{p2col 5 20 24 2: Matrices}{p_end}
{synopt:{cmd:e(b)}}coefficient vector{p_end}
{synopt:{cmd:e(Cns)}}constraints matrix{p_end}
{synopt:{cmd:e(ilog)}}iteration log (up to 20 iterations){p_end}
{synopt:{cmd:e(gradient)}}gradient vector{p_end}
{synopt:{cmd:e(V)}}variance-covariance matrix of the estimators{p_end}
{synopt:{cmd:e(V_modelbased)}}model-based variance{p_end}

{synoptset 20 tabbed}{...}
{p2col 5 20 24 2: Functions}{p_end}
{synopt:{cmd:e(sample)}}marks estimation sample{p_end}
{p2colreset}{...}


{title:Also see}

{psee}
Manual:  {help prdocumented:previously documented}

{psee}
{space 2}Help:  {manhelp ztp_postestimation R:ztp postestimation};{break}
{manhelp nbreg R},
{manhelp poisson R},
{manhelp svy_estimation SVY:svy estimation},
{manhelp tnbreg R},
{manhelp tpoisson R},
{manhelp zinb R},
{manhelp zip R},
{manhelp ztnb R}
{p_end}
