Trial Design and Oversight

Figure 1. Figure 1. Screening, Enrollment, and Follow-up of Barbershop Patrons. Other exclusion criteria included infrequent barbershop patronage (duration of <6 months or more than every 6 weeks between visits), an age younger than 35 years or older than 79 years, current treatment with dialysis or cancer chemotherapy, or plans to relocate.

In this trial, the barbershop was the unit of randomization. Participant group was determined according to barbershop (Figure 1; and Fig. S1 in the Supplementary Appendix, available with the full text of this article at NEJM.org). The trial was approved by institutional review boards at Cedars–Sinai Medical Center, Kaiser Permanente, and Westat (a survey company that conducted screening and enrollment and collected baseline and follow-up data), and the conduct of the trial was periodically reviewed by an independent data and safety monitoring board.18 Participants provided written informed consent. The authors vouch for the completeness and accuracy of the data and analyses and for the fidelity of the trial to the protocol, available at NEJM.org.

Trial Population

Field interviewers screened the clientele at participating black-owned barbershops to recruit self-identified regular patrons (≥1 haircut every 6 weeks for ≥6 months) who were non-Hispanic black men, 35 to 79 years of age, with systolic blood pressure of 140 mm Hg or more on two screening days (Figure 1). Women and persons receiving dialysis or chemotherapy were excluded.

Randomization and Interventions

Cluster randomization was necessary to avoid between-group contamination and to account for intraclass correlation.19,20 Barbershops were assigned to the intervention or to the active control approach in a 1:1 ratio in equally balanced blocks of four with the use of a prespecified random-number sequence. Participants and field interviewers were aware of the randomization assignments of the barbershops.

Barbers in shops assigned to the intervention were trained to encourage pharmacist follow-up and measure blood pressure. Before pharmacist intervention, providers signed a collaborative practice agreement. (See the Supplementary Appendix.) Two full-time doctoral-level pharmacists received specialized training and certification as hypertension clinicians and regularly reviewed each participant’s treatment with physician hypertension specialists (the first, sixth, and seventh authors). Pharmacists met regularly with participants in barbershops assigned to the intervention; the pharmacists prescribed an antihypertensive drug regimen, measured blood pressure, encouraged lifestyle changes, and monitored plasma electrolyte levels. The protocol called for the pharmacists to prescribe two-drug therapy that insurance would approve — preferably amlodipine plus a long-acting angiotensin-receptor blocker (ARB) or angiotensin-converting–enzyme (ACE) inhibitor — and to use the long-acting thiazide-type diuretic indapamide as the preferred third drug.21,22 Drug-class substitutions were allowed when medically indicated. After each encounter with a participant, pharmacists sent progress notes with their contact information to the given participant’s health care provider. If a given participant did not have a provider to sign the collaborative practice agreement, a designated community physician served as the supervising doctor.

Participants in the control group received instruction about blood pressure (Fig. S2 in the Supplementary Appendix). Barbers were trained to discuss the instructional information with participants and encourage follow-up with a provider.

Participants in both groups received resources to promote cohort retention and blood-pressure reduction: the results of two blood-pressure screenings, with follow-up recommendations and identification cards (Figs. S3 and S4 in the Supplementary Appendix); follow-up calls at 3 months; culturally specific health sessions; and vouchers for monthly haircuts. In intervention-group shops only, pharmacists interviewed participants to generate peer-experience stories (posted on shop walls), reviewed blood-pressure trends (Figs. S5 and S6 in the Supplementary Appendix), and gave participants $25 per pharmacist visit to offset the costs of generic drugs and transportation to pharmacies.

Trial Measurements

Field interviewers administered 30-minute, in-person, computer-based questionnaires in barbershops to participants in both groups at baseline and 6 months. These interviewers recorded blood pressure and structured response data on baseline characteristics, participant-reported outcomes, and prescription information transcribed from pill bottles.

All blood pressures were measured in barbershops with the use of a validated oscillometric monitor (Accutorr V, Mindray).23 To automate measurement and minimize dependence on operators, monitor readings were directly uploaded to a computer that electronically transmitted data to a secure website. (See the protocol.) At each visit, five sequential blood-pressure readings were obtained; the first two readings were discarded, and the last three readings were averaged.4 To reduce regression to the mean, the second screening blood pressure was taken as the baseline value.24 Field interviewers, pharmacists, and barbers were trained in proper measurement technique (with the participant seated after 5 minutes of rest and the arm resting at heart level and with no conversation with participants). The correct arm-cuff size was determined for each participant at the first screening and used throughout the trial.

For 6 months, pharmacists and some barbers measured blood pressure monthly to monitor drug therapy in the intervention group but not in the control group. The final 6-month blood pressures were recorded by field interviewers in the control group and by pharmacists in the intervention group to minimize the alerting reaction evoked by an unfamiliar data collector. The prespecified blood-pressure goal was less than 130/80 mm Hg — 5/5 mm Hg lower than the conventional out-of-office blood-pressure goal of less than 135/85 mm Hg25 — to account for blood-pressure variability. Pharmacists used a validated Clinical Laboratory Improvement Amendments–waived point-of-care device (i-STAT, Abbott Laboratories)26 to monitor plasma levels of electrolytes and creatinine after each medication change.

Trial Outcomes

Outcomes were measured as changes from baseline to 6 months. The prespecified primary outcome was systolic blood pressure. Secondary outcomes included diastolic pressure, rates of meeting blood-pressure goals, numbers of antihypertensive drugs, adverse drug reactions, self-rated health,3 and patient engagement according to a validated instrument.27 Acute kidney injury was defined as an increase in the plasma creatinine level of at least 0.3 mg per deciliter (30 μmol per liter) or a level at least 1.5 times the baseline level.28

Statistical Analysis

With an enrollment target of 10 barbershop clusters per trial group — 25 participants per cluster, a rate of cohort retention of 70%, and an estimated intraclass correlation coefficient of 0.014 — the initial design yielded 90% power to detect a 6.9 mm Hg greater reduction in systolic blood pressure at 6 months in the intervention group than in the control group, with a two-sided alpha level of 0.05. Because the total number of patrons per barbershop was much lower than anticipated, we increased the number of shops and grouped low-enrolling shops into clusters according to both enrollment date and geographic proximity, yielding 10 shop-clusters per group with at least 10 participants per cluster.29,30 The number of participants who withdrew from the trial was very small (Figure 1) and was considered to be random after extensive analysis.31

The intervention effect was estimated by means of a linear mixed-effects model, which included a random cluster effect. The primary predictor was an indicator for intervention group versus control group. Given the sample size, the model included three baseline covariates: baseline blood pressure, a doctor for routine medical care (yes vs. no), and high cholesterol level (yes vs. no). These were either strongly correlated with the dependent variable or showed baseline imbalance between the two groups. The linear mixed-effects model and its assumptions are described in the Supplementary Appendix.