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Question 9: An orthopedic surgeon observes that many of his patients coming in for total knee
replacement surgery played organized sports before the age of 10. He plans to collect more
extensive data on participation in organized sports from four patients undergoing knee
replacement surgery and to report the findings. Identify the type of study proposed and
indicate its specific strengths and weaknesses.

Answer: Consider that most of the patients coming for total knee replacement surgery used to
play organized sports before the age of 10. The surgeon decides to collect more broad data on
the participation of 4 patients (subjects) in organized sports (exposure) who have decided to
undergo knee replacement surgery (outcome). Thus, the given study is a case series study
because it is a study conducted for medical research that follow the subjects with a recognized
exposure and observes the medical records of the subjects for exposure and outcome. The
strengths of this study are that it has the capability to identify the new diseases by
observing the medical records of the subjects and it might generate the specific hypothesis of
relationship between the participation in organized sports (exposure) and knee replacement
surgery (outcome) that can be tested with even more extensive study. The weaknesses of this
study are that it does not include a control or comparison group in the sense that "the
participants who played organized sports and needed knee replacement surgery" are not
considered for comparison with "the participants who do not play organized sports and
needed knee replacement surgery". Also, this study considers small sample sizes (only 4
patients considered in the given study).

Question 10: Suggest an alternative design to address the hypothesis in Problem 9. What are
the major issues in addressing this hypothesis?

Answer: Referring to Problem 9, an alternative design can be a cohort design which will involve
two groups. One group would be of the participants who did not participate in organized
sports before the age of 10 and another group would be of the participants who did participate
in organized sports before the age of 10. The given study is prospective in nature and so this
study could alternatively register the children and follow those registered children through
their teenage and after that observe whether they require knee replacement surgery or not.
However, this alternative prospective study can be inefficient in the sense that it might take
many years to observe the relationship between the exposures (whether participating in
organized sports) and outcome (knee replacement surgery). So, a retrospective study will be
more efficient to than prospective cohort design in determining this relationship. On the other
hand, case-control study could be used for determining the relationship between the exposures
(whether participating in organized sports) and outcome (knee replacement surgery) by
enrolling the participants who undergo knee replacement surgery (cases) in one group and the
participants who did not undergo knee replacement surgery (controls) in another group. Then,
these groups can be compared by assessing each participant for their participation in organized
sports before age of 10.