Table 4.

Pharmacoepidemiologic Studies that Provided Analysis for Validating the Assumptions of Negative Controls

First Author, Year (Reference No.)	Study Design	Type of Data Used	Hypothesized Causal Association	Primary Study Effect Measure	Type of NC	Types of Bias as Reported by Study	Statistical Approach Used to Test the Underlying Assumptions of NC
Ivers, 2015 (57)	Case-control study	Primary data collected for the study	Exposure: receipt of oral inactivated bivalent whole-cell cholera vaccine; outcome: acute watery diarrhea with a stool sample positive for cholera	Relative risk	NCO: acute watery diarrhea with a stool sample that tested negative for cholera	Not specified	Study showed the distributions of factors related to clinical presentation and treatment for cholera (time from symptom onset to admission, serotype, dehydration stage at presentation, treatment received at clinic, volume of oral rehydration solution given in clinic, volume of intravenous fluid given in clinic, admitted overnight to the cholera treatment unit, duration of stay at cholera treatment unit, and the discharge outcome type), age, gender, participation response rate, earthen floor in home, ever attended school, electricity in house, number of people in household, whether agriculture is the main source of income, whether main toilet is a latrine, ever admitted to a cholera treatment unit overnight, household member with cholera in the previous week, household member ever spent a night in a cholera treatment unit, and household member with diarrhea in the previous week across the NCO and the main outcome groups.
Lazarus, 2016 (72)	Cohort study	Main study: data from an existing cohort study; replication study: integrated health system data	Exposure: use of proton pump inhibitors; outcome: chronic kidney disease	HR	NCE: use of histamine H2-receptor antagonists	Not specified	Study provided the distributions of age, gender, race, education, health insurance, annual household income, estimated glomerular filtration rate, ratio of urinary albumin to creatinine, smoking, body mass index, systolic blood pressure, prevalent medical conditions, and concomitant medication use for the NCE group along with the primary exposure and the control group.
Han, 2017 (50)	SCCS	Administrative claims	Exposure: concomitant use of a precipitant of interest (vs. not receiving a precipitant) with secretagogues; outcome: serious hypoglycemia	Rate ratio	NCE: concomitant use of a precipitant of interest with metformin	Confounding bias by inherent hypoglycemic effects of the precipitants	Study provided the distributions of gender, median age, and proportion of cases receiving antidiabetics other than secretagogues in the past 30 days before events across the NCE and the primary exposures.
Dillon, 2019 (34)	Cohort study	Pharmacy dispensing data, primary data collected for the study	Exposure: gaps in antihypertensive medication adherence; outcome: injurious fall	Relative risk	NCE: gaps in antithrombotic medication adherence	Confounding bias resulting from healthy adherer bias	Study checked for the distribution of covariates across the exposure (antihypertensive) sample and the NCE (antithrombotic) samples. They found statistically significantly different distributions for gender, comorbidities, and rate of regular medication use between the exposure and the NCE samples. Accordingly, the NCE sample was reweighted using inverse probability weighting, with weights being the ratio of the predicted probabilities using 2 probit regressions, one with and one without statistically different participant characteristic variables of gender, comorbidities, and rate of regular medication use.
Markovic, 2019 (83)	Cohort study	Data from an existing cohort study	Exposure: maternal exposure to NSAIDs during pregnancy; outcome: neurodevelopmental outcomes (attention problem score) in children	Mean difference	NCE: maternal NSAIDs use before pregnancy; NCO: somatic complaints in children	Confounding bias	Study provided the distributions of child factors (gender, birth weight, gestational age at birth, and Apgar score at 5 minutes after birth) and maternal factors (age, ethnicity, education, family income, body mass index, smoking during pregnancy, alcohol use during pregnancy, psychopathology symptoms, cognitive ability score, and concomitant-medication use) for the NCE and the exposure.
Ray, 2019 (104)	Case-control study	EHR	Exposure: receipt of inactive influenza vaccine; outcome: positive test result for any influenza virus	OR	NCO: positive test result for respiratory syncytial virus	Confounding bias	Study provided the distributions of age, gender, Diagnostic Cost Group risk score, influenza vaccination in previous season, year, number of days from September 1 to vaccination, and number of days from vaccination to influenza test for the NCO and the primary outcome. The study also mentioned that the known differential risk factors between the outcome and the NCO are related to age, and that the study adjusted for age and removed ages below 2 years old. Study also cited earlier research that found similar characteristics between respiratory syncytial virus and influenza A in relation to demographic characteristics, chronic illnesses, residence in long-term care facilities, and smoking.
Tien, 2020 (128)	Cohort study	Primary data collected for the study	Exposure: chlorhexidine gluconate bathing (vs. over-the-counter non–chlorhexidine-based antibacterial soap or cleansing lotion); outcome: gram-positive cocci-related, skin flora–related, or central line-associated bloodstream infection	HR	NCO: gut-origin bacteremia	Confounding bias, participation bias	Study provided the results of regression analysis for the NCO with the same set of covariates that were used in the regression analysis for the primary outcome. The covariates included 2% chlorhexidine daily bathing, age, gender, diagnosis of hematological, relapsed/refractory diseases, postchemotherapy neutropenia, autologous peripheral blood stem cell transplantation, chemotherapy, central venous catheter use, portacath use, oral ciprofloxacin/levofloxacin for prophylaxis, oral sulfamethoxazole/trimethoprim for prophylaxis, multidrug-resistant organism carriage, diabetes, and hospital mortality. Results for both the univariate and multivariate analyses were provided across the primary outcome and the NCO. In the univariate analysis of the primary outcome, 2% chlorhexidine daily bathing, post-chemotherapy neutropenia, central venous catheter use, and oral ciprofloxacin/levofloxacin for prophylaxis were statistically significant. In the univariate analysis of the NCO, 2% chlorhexidine daily bathing, post-chemotherapy neutropenia, chemotherapy, and oral ciprofloxacin/levofloxacin for prophylaxis were statistically significant.
Zhou, 2020 (154)	SCCS	Administrative claims	Exposure: concomitant use of a precipitant of interest (vs. not receiving a precipitant) with anticoagulants (anticoagulant-precipitant pairs); outcome: thromboembolism (a composite outcome of stroke and venous thromboembolism)	Rate ratio	NCE: concomitant use of a precipitant of interest with pravastatin (pravastatin-precipitant pairs)	Confounding bias by inherent effect of the precipitant on the primary outcome	Study provided the distributions of gender, age, and baseline medical conditions (prior diagnoses of atrial fibrillation, stroke, serious bleeding, cirrhosis, chronic kidney disease, and hypertension), prior prescription of nonsteroidal antiinflammatory drugs in the 30 days prior to initiation of oral anticoagulant or pravastatin, and prior prescription of antiplatelet agents in the previous 30 days) across the NCE and the primary exposures.

Abbreviations: EHR, electronic health records; HR, hazard ratio; NC, negative control; NCE, negative control exposure; NCO, negative control outcome; NSAID, nonsteroidal antiinflammatory drug; OR, odds ratio; SCCS, self-controlled case series.