Logistic effect plot not corresponding to max likelihood table

[pink_poodle]

I am doing reference cell coding with a binary categorical predictor.

According to max likelihood table,

Intercept = 0.2335, and that is the predicted logit probability of the reference level.

However, the effect plot shows a dot at >0.50 for the predicted probability of that level.

Why is that? Please let me know possible explanations.

proc logistic data=have plots(only)=(effect oddsratio);
    class x(ref='<=60 min')/ param=ref;
    model y(event='1')= x / clodds=pl;
run;

[Rick_SAS]

Can you upload the image so we can see it?

[pink_poodle]

maximum likelihood tableeffect plot

[Rick_SAS · Accepted solution]

You can get the exact predicted values by using

ods output effectplot=EFPLOT;

proc logistic....

run;

proc print data=EFPLOT; run;

The estimate for the Intercept (reference level) is 0.2335.

Then the predicted value for the reference category is 

p = logistic( 0.2335 );

which is 0.5581. This looks like the height of the dot for the reference category, so it looks like all is well. If the height is different from 0.5581, let me know.

[pink_poodle]

The ods output value is 0.558105622519328. Thank you!

[pink_poodle]

Double-checked the logistic function:

logit(p) = ln(odds) 

let logit(p) = a

odds = p / ( 1 - p )

p / (1 - p) = e^a

p  = e^a - p*e^a

p*(1 + e^a) = e^a

p = e^a / (1 + e^a) = logistic(a)

[Rick_SAS]

Yes. Equivalently, p = 1 / (1 + exp(-a)), which is shorter to write.