I have binary data for which 70% involve 1 (yes) and 30% involve 0 (no). I've done logistic regression in MedCalc. Results below:

Sample size 60

Positive cases a 42 (70,00%)

Negative cases b 18 (30,00%)

a Bacteria = 1

b Bacteria = 0

Overall Model Fit

Null model -2 Log Likelihood 73,304

Full model -2 Log Likelihood 0,0000000536

Chi-squared 73,304

DF 1

Significance level

**P < 0,0001**

Cox & Snell R2 0,7053

Nagelkerke R2 1,0000

Coefficients and Standard Errors

Variable Coefficient Std. Error Wald P

Number -38,25476 12213,08792 0,000009811 0,9975

Constant 1625,82574 519083,33787 0,000009810 0,9975

Could anyone explain why there is so small chi-square p-value and what does it mean, and also the Wald(0,000009811) an P (0,9975).

Those results show low probability which is puzzling because proportion 70/30 is not that big. Am I doing something wrong here?

I would appreciate for any help,

Thanks,

Agata