The following figure displays results from a systematic review and meta‐analysis of the effects of sun exposure on mental health.The RRs represent the association between
Higher sun exposure and good mental health.Studies 1, 2 and 5 are cohort studies, 3 and 4
Are case‐control studies.They are arranged in order of year of publication, earliest first. Which of the following statements are true? (Select all that apply) The summary
Result of the meta‐analysis:
A)Tells us for certain that sunlight is good for mental health
B)Is meaningless because of the extreme heterogeneity of the RRs
C)Is of practical public health importance
D)Is helpful in assessing whether the relation might be causal
E)Is statistically significant

Question

The following figure displays results from a systematic review and meta‐analysis of the effects of sun exposure on mental health.The RRs represent the association between
Higher sun exposure and good mental health.Studies 1, 2 and 5 are cohort studies, 3 and 4
Are case‐control studies.They are arranged in order of year of publication, earliest first.  Which of the following statements are true? (Select all that apply) The summary
Result of the meta‐analysis:
A)Tells us for certain that sunlight is good for mental health 
B)Is meaningless because of the extreme heterogeneity of the RRs 
C)Is of practical public health importance 
D)Is helpful in assessing whether the relation might be causal 
E)Is statistically significant

Quizplus · Accepted Answer

E is clearly correct, as the lower bound of the CI is greater than 1;
combining results across the studies decreases the likelihood of chance as an
explanation for the association.D is also correct as the summary RR gives the best
overall expectation of the true strength of the relation IF we do not think the
heterogeneity is so great that it is inappropriate to combine the data across studies, i.e.
that B is not correct.In this situation all of the estimates are >1.0 so this assumption is
probably not too unreasonable, although it is notable that the retrospective case‐
control studies (3 & 4), which would be more susceptible to selection and recall bias,
have given much higher estimates than the cohort studies.Excluding the case‐control
studies would have given a much lower pooled RR.[NB In assessing heterogeneity we
are also assessing the consistency of the evidence across studies and study types, again
contributing to an assessment of causation.] Before we could conclude that C was true
we would need more information on how important a 35% increase in mental health, as
measured here, could be.To establish A we would need more information (e.g.
regarding the likely validity of the study results) and to do a formal causal analysis,
taking account of a number of factors in addition to the strength of association
(relatively small in this instance - especially if we put more emphasis on the results
from the cohort studies).

The Following Figure Displays Results from a Systematic Review and Meta‐analysis