Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: st: problem with predicted probabilities
From
Richard Williams <[email protected]>
To
[email protected], [email protected]
Subject
Re: st: problem with predicted probabilities
Date
Sun, 02 Feb 2014 16:23:40 -0500
Getting every case classified as 0 (or 1) is not unusual. For
relatively rare events, the highest predicted probability for every
case may be less than .5, so every case gets classified as 0. My own
experience is that the classification table tends not to be that
helpful, especially for events that are very rare or very common.
At 04:58 AM 2/2/2014, Witness Chirinda wrote:
Dear Statalist
I want to obtain some predicted probabilities after logistic
regression, as attached. I want to use the predicted probabilities in
my next step instead of observed prevalence since the latter are
adjusted for other (socio-demographic) factors.
My problem is that the when I run - estat classification- it giving 0s
for + classification. I am sure I am doing it the wrong way somewhere.
Please see below output. All variables used in the model have been
recorded to be binary 1/0
Thanks for any help!
------------------
. logistic Health_stat age maried wealth educat place sex
Logistic regression Number of obs = 2339
LR chi2(6)
= 50.61
Prob > chi2
= 0.0000
Log likelihood = -996.02516 Pseudo R2 = 0.0248
------------------------------------------------------------------------------
Health_stat | Odds Ratio Std. Err. z P>|z| [95%
Conf. Interval]
-------------+----------------------------------------------------------------
age | 1.109083 .0342696 3.35 0.001 1.043909 1.178326
maried | 1.2134 .1962535 1.20 0.232 .8837556 1.666004
Wealth | 1.430957 .1784661 2.87 0.004 1.120641 1.827203
educat | 1.670411 .2010455 4.26 0.000 1.319397 2.11481
place | .9334522 .1223134 -0.53 0.599 .7220318 1.206779
sex | 1.129008 .1324642 1.03 0.301 .8970722 1.420911
. estat class
Logistic model for poorSRHS
-------- True --------
Classified | D ~D | Total
-----------+--------------------------+-----------
+ | 0 0 | 0
- | 370 1969 | 2339
-----------+--------------------------+-----------
Total | 370 1969 | 2339
Classified + if predicted Pr(D) >= .5
True D defined as poorSRHS != 0
--------------------------------------------------
Sensitivity Pr( +| D) 0.00%
Specificity Pr( -|~D) 100.00%
Positive predictive value Pr( D| +) .%
Negative predictive value Pr(~D| -) 84.18%
--------------------------------------------------
False + rate for true ~D Pr( +|~D) 0.00%
False - rate for true D Pr( -| D) 100.00%
False + rate for classified + Pr(~D| +) .%
False - rate for classified - Pr( D| -) 15.82%
--------------------------------------------------
Correctly classified 84.18%
--------------------------------------------------
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/faqs/resources/statalist-faq/
* http://www.ats.ucla.edu/stat/stata/
-------------------------------------------
Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME: (574)289-5227
EMAIL: [email protected]
WWW: http://www.nd.edu/~rwilliam
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/faqs/resources/statalist-faq/
* http://www.ats.ucla.edu/stat/stata/