Table 2.

Factors to Consider in the Design and Analysis of Longitudinal Studies

Factor	Yes	No	Uncertain
Have exposed and nonexposed study subjects been selected from similar at risk populations? Has the investigator presented a sufficient rationale for the choice of the study population and its potential generalizability?	□	□	□
Was exposure status been adequately measured, categorized, and independently validated?	□	□	□
Have possible changes in exposure status since the time of initial baseline classification been measured and taken into account in the analysis?	□	□	□
Have the study endpoints been determined without regard to exposure status and are the persons involved in the collection of these data unaware of the primary study hypotheses?	□	□	□
Was determination of the principal study outcome adequately measured and independently validated?	□	□	□
Have potentially confounding factors been measured and has the influence of these factors been controlled for analytically?	□	□	□
Was an acceptable means of determining subject follow-up used and was a high follow-up rate (e.g., >80%) been achieved?	□	□	□
If an acceptable follow-up rate of exposed and nonexposed cohorts was not achieved, have the characteristics of those unavailable for follow-up been compared with those remaining under follow-up to determine whether these groups are comparable?	□	□	□
Did the study have adequate power to detect differences in the principal study outcome(s) in exposed and nonexposed cohorts?	□	□	□
Were there an adequate number of individual study endpoints or was a composite endpoint created either after the study was completed or a priori?
Was the duration of follow-up sufficient?	□	□	□
Were incidence rates of disease calculated and relative risks and accompanying confidence intervals presented?	□	□	□
Were the study results clearly presented and adequately interpreted?	□	□	□
Were the study strengths and limitations clearly acknowledged?	□	□	□