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Effect of patient withdrawal on a study evaluating pharmacist management of hypertension . STUDY OBJECTIVES To examine potential threats to internal and external study validity caused by differential patient withdrawal from a randomized controlled trial evaluating pharmacist management of hypertension , to compare the characteristics of patients who withdrew with those of patients who completed the study , and to identify characteristics that predispose patients to withdraw from hypertension management . DESIGN Prospective , randomized , comparative study . SETTING Network of primary care clinics . PATIENTS Four hundred sixty-three patients with a diagnosis of hypertension and a last documented systolic blood pressure of 160 mm Hg or greater and/or diastolic blood pressure of 100 mm Hg or greater . INTERVENTION Patients were randomly allocated to the pharmacist intervention or usual-care ( control ) group . Those in the pharmacist intervention group were collaboratively managed by a primary care clinical pharmacy specialist and their primary care provider . Patients in the control group received usual care from only their primary care provider . MEASUREMENTS AND MAIN RESULTS Of the 463 patients , 191 ( 41 % ) withdrew from the study after randomization and 272 ( 59 % ) completed the study . Patients who withdrew from the pharmacist intervention group were similar to patients who withdrew from the usual-care group with respect to age , sex , insurance status , and chronic conditions . Patients who smoked or had commercial insurance were more likely to withdraw from the study than the other participants . However , multivariate analysis of all variables , when adjusted for the effect of the intervention , revealed that insurance status was the only variable associated with a heightened probability of withdrawal ( p=0.002 ) . CONCLUSION Although this study had a high withdrawal rate , between-group patient characteristics remained balanced . Therefore , internal validity was preserved , and outcomes from the study groups could be reliably compared . A lack of significant differences between patients who withdrew versus those who completed , with the exception of insurance status , suggests that external validity was not jeopardized .
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Intervention_Other
pharmacist management of hypertension
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Intervention_Other
pharmacist intervention
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Intervention_Control
usual-care ( control ) group
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Intervention_Educational
collaboratively managed by a primary care clinical pharmacy specialist and their primary care provider
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Intervention_Educational
received usual care from only their primary care provider
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Intervention_Other
pharmacist intervention
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Outcome_Other
withdraw
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Outcome_Other
insurance status
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Outcome_Other
withdrawal
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Participant_Condition
patient withdrawal on a study
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Participant_Condition
hypertension
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Participant_Sample-size
Four hundred sixty-three patients
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Participant_Condition
hypertension
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Participant_Condition
a last documented systolic blood pressure
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Participant_Condition
diastolic blood pressure
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Participant_Sample-size
463
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Participant_Sample-size
191
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Participant_Sample-size
272