Case-Only Designs in Pharmacoepidemiology: A Systematic Review

<div><h3>Background</h3><p>Case-only designs have been used since late 1980’s. In these, as opposed to case-control or cohort studies for instance, only cases are required and are self-controlled, eliminating selection biases and confounding related to control subjects, and time-invariant characteristics. The objectives of this systematic review were to analyze how the two main case-only designs – case-crossover (CC) and self-controlled case series (SCCS) – have been applied and reported in pharmacoepidemiology literature, in terms of applicability assumptions and specificities of these designs.</p> <h3>Methodology/Principal Findings</h3><p>We systematically selected all reports in this field involving case-only designs from MEDLINE and EMBASE up to September 15, 2010. Data were extracted using a standardized form. The analysis included 93 reports 50 (54%) of CC and 45 (48%) SCCS, 2 reports combined both designs. In 12 (24%) CC and 18 (40%) SCCS articles, all applicable validity assumptions of the designs were fulfilled, respectively. Fifty (54%) articles (15 CC (30%) and 35 (78%) SCCS) adequately addressed the specificities of the case-only analyses in the way they reported results.</p> <h3>Conclusions/Significance</h3><p>Our systematic review underlines that implementation of CC and SCCS designs needs to be more rigorous with regard to validity assumptions, as well as improvement in results reporting.</p> </div

Flowchart of selected articles.

<p>Flowchart of selected articles.</p

Statistical Issues.

a<p>One report used both CC and SCCS.</p>b<p>Conditional logistic regression for the CC and conditional Poisson regression for SCCS.</p>c<p>CC: Odds Ratio, Relative risk, Rate Ratio/Incidence Rate Ratio; SCCS: Relative Risk, Relative Incidence, Incidence Rate Ratio.</p

Additional file 1 of On the use of propensity scores in case of rare exposure

Data-generation process and simulated scenarios. (DOCX 119 kb

General Characteristics of the Studies Using Case-Crossover and/or Self-Controlled Case Series Designs.

a<p>Two reports used both CC and SCCS.</p>b<p>e.g.: bias due to fixed-confounders.</p>c<p>e.g.: suitable database, no representative control group available, necessity of easy, rapid, simple design.</p

Characteristics of Risk and Control Periods.

<p>Characteristics of Risk and Control Periods.</p

Validity Assumptions for Use of Case-Crossover and Self-Controlled Case Series Designs.

<p>Validity Assumptions for Use of Case-Crossover and Self-Controlled Case Series Designs.</p

Number of reports per year of studies using case-crossover or self-controlled case series designs.

<p>Number of reports per year of studies using case-crossover or self-controlled case series designs.</p

Characteristics of Exposures and Data Sources of the Studies.

a<p>Two reports used both CC and SCCS.</p>b<p>Administrative database: reimbursement database, hospital or institutional records, primary care database (THIN, GRPD).</p>c<p>Data collected for the study: self-questionnaire, diary, telephone call, web site, interview, individual health booklet.</p>d<p>Pre-existing studies: register, clinical/cohort data.</p

Main Specific Methodological Points to Consider in Planning and Reporting Case-only Studies (to be considered as a complement of the STROBE Statement).

<p>Main Specific Methodological Points to Consider in Planning and Reporting Case-only Studies (to be considered as a complement of the STROBE Statement).</p