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Stata Technical Bulletin

STB-33


For the variable black:

. regpred2 chi age, adj(race) from(40) to(SO) one(raceb) zero(racew)

And for the variable asian:

. regpred2 chi age, adj(race) from(40) to(80) zero(racew raceb)

regpred2 will not permit the user to specify the same variable to be set to both one and zero. The attempt to do so will
generate an “error 198”.

Examples of the level() and inst() options

Another change introduced in regpred2 is to allow the confidence intervals displayed in the graphs and presented in the
predictions to differ from 95%. regpred2 implements the standard Stata convention of defaulting to a confidence level set by
the S-Ievel macro. The S-Ievel macro can be overridden by including among the regpred2 options, the option level(
#),
where
# is the desired confidence interval expressed as a percentage.

Here are examples of the application of the lev el(#) and the in st iivlist') options. The data used is that in Garrett’s insert
in STB-26. First, apply regpred2 as regpred could have been applied, only adding the level(#) option to demonstrate how it
works. Here is the output, including the predicted values and 90% intervals in Figure 1.

. regpred2 chi sbp, f(60) t(300) i(20) adj(age smk) level(90) xlabel ylabel

Source I

SS

df       MS

Number of obs

F( 3, 1214)

=    1218

=    0.37

_________-|-_

Model I

1771.65999

3   590.55333

Prob > F

= 0.7732

Residual

1927027.32

1214 1587.33716

R-Squared

Adj R-Squared

= 0.0009

= -0.0016

---------+_

Total I

1928798.98

1217 1584.88001

Root MSE

= 39.841

chi I

Coef.

Std. Err.       t

p>t

[907. Conf.

Interval]

sbp I

.0404827

.0438582      0.923

0.356

-.0317128

.1126782

age I

-.0632856

.131533     -0.481

0.631

-.2798034

.1532323

smk I

-1.328942

2.399776     -0.554

0.580

-5.279237

2.621353

-Cons I

210.093

8.212943     25.581

0.000

196.5736

223.6124

Predicted Values and 90% Confidence Intervals

Outcome Variable:     Serum cholesterol — chi

Independent Variable: Systolic blood pressure — sbp

Covariates:           age smk

Instruments :

Variables set to Zero:

Variables set to One:

Total Observations: 1218

Confidence interval: 90

sbp

pred_y

lower

upper

1.

60

208.2786

201.8328

214.7245

2.

80

209.0883

204.0052

214.1713

3.

100

209.8979

206.1179

213.678

4.

120

210.7076

208.0801

213.3351

5.

140

211.5172

209.5984

213.4361

6.

160

212.3269

210.1766

214.4772

7.

180

213.1365

210.0174

216.2556

8.

200

213.9462

209.5876

218.3048

9.

220

214.7558

209.0612

220.4505

10.

240

215.5655

208.4927

222.6383

11.

260

216.3752

207.9027

224.8476

12.

280

217.1848

207.3002

227.0694

13.

300

217.9945

206.69

229.2989



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