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- 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
time.
- 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.
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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 ...