22
Stata Technical Bulletin
STB-48
Syntax
dagumfit incvar ^veight] [if exp∖ [in range] [, stats cdîOcdfname) pdf (pdfaame)
level(#) nolog trace b0(#) d0(#) h0(#)]
fweights and aweights are allowed.
To reset problem-size limits, see help matsize.
Options
stats displays selected distributional statistics implied by the Dagum model parameter estimates: percentiles, cumulative shares
of total income at percentiles (i.e., the Lorenz curve ordinates), the mean, standard deviation, variance, half the coefficient
of variation squared, Gini coefficient, and percentile ratios p90∕p10, p75∕p25.
cdf Cdffaame) creates a new variable cdfname containing the estimated Dagum cdf value F (ж) for each x.
pd±(pdfname) creates a new variable pdfname containing the estimated Dagum pdf value /(ж) for each ж.
level(#) specifies the confidence level, in percent, for confidence intervals. The default is level(95) or as set by set level;
see [U] 26.4 Specifying the width of confidence intervals.
nolog suppresses the iteration logs.
trace reports the current value of the estimated parameters at each iteration. See [R] maximize.
bO(#), d0(#), h0(#) allow the user to specify starting values for the Dagumparameters. Default starting values are b = exp(4),
0 = exp(0.1), and h = 1 + exp(13).
Saved results
The global macros set by ml post, plus
S_b, S_d, S_h estimated parameters 6, d, h, respectively
Access to estimated coefficients (transformations of the parameters) and their standard errors are available in the usual way;
see [U] 20.5 Accessing coefficients and standard errors, and [R] matrix get.
Examples
The illustrative examples use the same income distribution data as described in Jenkins (1999). The income variable is
eybhc with fweight variable wgt.
In order to compare the results of smfit and dagumfit, the former is run excluding nonpositive values of eybhc. The
Singh-Maddala distribution is defined for nonnegative incomes but the Dagum distribution only for positive incomes. The results
are as follows:
. smfit eybhc [fw = wgt] if eybhc>0t stats cdf(smF) pdf(smf)
Iteration 0: Log Likelihood = -40547.317
Iteration 1: Log Likelihood = -40062.416
Iteration 2: Log Likelihood = -39888.368
Iteration 3: Log Likelihood = -39879.841
Iteration 4: Log Likelihood = -39879.785
Iteration 5: Log Likelihood = -39879.785
ML fit of Singh-Maddala distribution Number of obs = 6448
Model chi2(0)
Prob > chi2 =
Log Likelihood = -39879.7845655
— |
eybhc I |
Coef. |
Std. Err. |
z |
P>∣z∣ |
[957. Conf. |
— Interval] |
— pi |
I _cons I |
.5637748 |
.0298546 |
18.884 |
0.000 |
.505261 |
— .6222887 |
— p2 |
I _cons I |
5.357418 |
.0291111 |
184.033 |
0.000 |
5.300361 |
— 5.414475 |
— p3 |
I _cons I |
.178296 |
.0513498 |
3.472 |
0.001 |
.0776523 |
— .2789397 |