An investigator wishes to study the relationship between lidocaine and bupivacaine given for spinal anesthesia and transient radicular irritation (TRI). At his institution most D&C's are performed under lidocaine spinal anesthesia, and most knee arthroscopies are performed under bupivacaine and fentanyl spinal anesthesia. After excluding those with diabetes, he uses these patients for his study groups, and he's able to review 100 charts: 50 lidocaine, 50 bupivacaine/fentanyl. He notes that 8% of the lidocaine patients and 4% of the bupivacaine patients develop TRI.
He concludes that spinal lidocaine causes TRI.
1) Which of the following statements concerning subject assignment is true?
a) Because patients were included in
the study by chance, this is an example of a randomized sample.
b) Because the investigator didn't assign patients to study groups, this is
an example of observed assignment.
c) Because the treating physicians didn't know that these patients would be
studied, there is no selection bias in this study.
d) Because the patients weren't randomized, this study can provide no useful
conclusions.
e) None of the above.
2) The compontent(s) of the definition of a confounding variable (confounder) is/are:
1) It isn't germane to the association under investigation.
2) It may be a determinant of outcome.
3) It isn't randomly distributed among the study groups.
4) It makes the investigation more difficult.
A-1,2,3
B-1,3
C-2,4
D-4 only
E-all
3) Confounders in the study described above may include:
1) Surgical position
2) Fentanyl
3) Patient gender
4) Diabetes
A-1,2,3
B-1,3
C-2,4
D-4 only
E-all
4) To establish a cause-effect relationship an investigator must show:
1) statistically significant association between the putative
cause and the effect.
2) that the putative cause proceeds the effect.
3) that altering the cause alters the effect.
4) that multiple investigators have reported the relationship.
A-1,2,3
B-1,3
C-2,4
D-4 only
E-all
5) In the study described above the criteria for a cause-effect relationship that the investigator satisfied were:
a) a statistically significant association between the putative
cause and the effect.
b) that the putative cause precedes the effect.
c) that altering the cause alters the effect.
d) that multiple investigators have reported the relationships.
e) none of the above.
6) The investigation(s) which can establish a cause-effect relationship is/are:
1) Case series.
2) Case-control studies.
3) Cohort studies.
4) Randomized clinical trials.
Robert Kettler, MD
