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I was asked to provide information some more information about the data:

• N total = 300
• n disease = 25
• n censored = 150

Because some paticipants missed follow-up (they dropped out or deceased) my data is right-censored. Cox regression demonstrated my cut-off as significant predictor, however, this analysis was performed on the non-censored sample resulting in selection bias.

If no, does anbyody have any advice to account for the selection bias in my sample?

ID   disease   months   censored   cutoff
a    0          66        0          0
c    1          30        0          1
e    0          45        0          0

coxph(Surv(months, disease)
          ~cutoff,
           covariates,
          data = dat)

ID   disease   months   censored   cutoff
a    0          0         0          0
a    0          66        0          0
*b*  0          0         1          0
c    0          0         0          1
c    1          30        0          1
*d*  0          0         0          1
e    0          0         0          0
e    0          45        0          0

coxph(Surv(months, disease)
          ~score,
           covariates,
          data = dat)

... But as my goal is to predict whether particpants developed the disease at follow-up and not at baseline, I am unsure whether this analysis answers another statistical question than mine.

Because some participants missed follow-up (they dropped out or deceased) my data is right-censored. Cox regression demonstrated my cut-off as significant predictor, however, this analysis was performed on the non-censored sample resulting in selection bias.

If no, does anybody have any advice to account for the selection bias in my sample?

ID   disease   months   censored   cutoff
a    0          66        0          0
c    1          30        0          1
e    0          45        0          0

coxph(Surv(months, disease)
          ~ cutoff,
           covariates,
          data = dat)

ID   disease   months   censored   cutoff
a    0          0         0          0
a    0          66        0          0
*b*  0          0         1          0
c    0          0         0          1
c    1          30        0          1
*d*  0          0         0          1
e    0          0         0          0
e    0          45        0          0

coxph(Surv(months, disease)
          ~ score,
          covariates,
          data = dat)

... But as my goal is to predict whether participants developed the disease at follow-up and not at baseline, I am unsure whether this analysis answers another statistical question than mine.

I have data from a prospective study with two measurements per participant (baseline and follow-up). I am interested in whether a score obtained at baseline predicts disease development at follow-up, taking interval between baseline and follow-up into account (time interval differs for each participant).

Because some paticipants missed follow-up (they dropped out or deceased) my data is right-censored. Cox regression demonstrated my score as significant predictor, however, this analysis was performed on the non-censored sample resulting in selection bias.

ID   disease   months   censored   score
a    0          66        0          0
c    1          30        0          1
e    0          45        0          0

coxph(Surv(months, disease)
          ~score,
           covariates,
          data = dat)

ID   disease   months   censored   score
a    0          0         0          0
a    0          66        0          0
*b*  0          0         1          0
c    0          0         0          1
c    1          30        0          1
*d*  0          0         0          1
e    0          0         0          0
e    0          45        0          0

I have data from a prospective study with two measurements per participant (baseline and follow-up). I am interested in whether a cut-off (binary) obtained at baseline predicts disease development at follow-up, taking interval between baseline and follow-up into account (time interval differs for each participant).

Because some paticipants missed follow-up (they dropped out or deceased) my data is right-censored. Cox regression demonstrated my cut-off as significant predictor, however, this analysis was performed on the non-censored sample resulting in selection bias.

ID   disease   months   censored   cutoff
a    0          66        0          0
c    1          30        0          1
e    0          45        0          0

coxph(Surv(months, disease)
          ~cutoff,
           covariates,
          data = dat)

ID   disease   months   censored   cutoff
a    0          0         0          0
a    0          66        0          0
*b*  0          0         1          0
c    0          0         0          1
c    1          30        0          1
*d*  0          0         0          1
e    0          0         0          0
e    0          45        0          0