- When research involves time-related variables, such as
survival and recurrence, we generally do not know the outcome for
all patients at the time the study is published, so these outcomes
are called censored.
- Observations are doubly censored when not all patients enter
the study at the same time.
- An example of why special methods are needed to analyze survival
data helps illustrate the logic behind them.
- Life table or actuarial methods were developed to show survival
curves; although generally surpassed by Kaplan–Meier curves,
they occasionally appear in the literature.
- Survival analysis gives patients credit for how long they
have been in the study, even if the outcome has not yet occurred.
- The Kaplan–Meier procedure is the most commonly used
method to illustrate survival curves.
- Estimates of survival are less precise as the time from entry
into the study becomes longer, because the number of patients in
the study decreases.
- Survival curves can also be used to compare survival in two
or more groups.
- The logrank statistic is one of the most commonly used methods
to learn if two curves are significantly different.
- The hazard ratio is similar to the odds ratio; the difference
is that the hazard ratio compares risk over time, while the odds
ratio examines risk at a given time.
- The Mantel–Haenszel statistic is also used to compare
curves, not just survival curves.
- Several versions of the logrank statistic exist. The logrank
statistic assumes that the risk of the outcome is the constant over
- The Mantel—Haenszel statistic essentially combines
a number of 2 × 2 tables for an overall
measure of difference.
- The hazard function gives the probability that an outcome
will occur in a given period, assuming that the outcome has not
occurred during previous periods.
- The intention-to-treat principle states that subjects are
analyzed in the group to which they were assigned. It minimizes
bias when there are treatment crossovers or dropouts.
Lung cancer is the leading cause of cancer deaths in men and
in women between the ages of 15 and 64 years of age. Small-cell
lung cancer accounts for 20–25% of all cases of
lung cancer. At the time of diagnosis, 40% of the patients
with small-cell cancer have disease confined to the thorax (limited
disease) and 60% have metastases outside of the thorax
(extensive disease). Current standard chemotherapy for extensive
disease using a combination of cisplatin and etoposide yields a
median survival of 8–10 months and a 2-year survival rate
of 10%. Preliminary studies using a combination of cisplatin
with irinotecan resulted in a median survival of 13.2 months. For this
reason, Noda and colleagues (2002) at the Japan Clinical Oncology
Group conducted a prospective, randomized clinical trial to compare
irinotecan plus cisplatin with etoposide plus cisplatin. The primary
endpoint was overall survival. Secondary endpoints included rates
of complete and overall response. A complete response was defined
as the disappearance of all clinical and radiologic evidence of
a tumor ...