A theory-based process evaluation alongside a randomised controlled trial of printed educational messages to increase primary care physicians' prescription of thiazide diuretics for hypertension [ISRCTN72772651].
Pragmatic trials of implementation interventions focus on evaluating whether an intervention changes professional behaviour under real-world conditions rather than investigating the mechanism through which change occurs. Theory-based process evaluations conducted alongside pragmatic randomised trials address this by assessing whether the intervention changes theoretical constructs proposed to mediate change. The Ontario Printed Educational Materials (PEM) cluster trial was designed to increase family physicians' guideline-recommended prescription of thiazide diuretics. The trial found no intervention effect. Using the theory of planned behaviour (TPB), we hypothesised that changes in thiazide prescribing would be reflected in changes in intention, consistent with changes in attitude and subjective norm, with no change to their perceived behavioural control (PBC), and tested this alongside the RCT.



We developed and sent TPB postal questionnaires to a random sub-sample of family physicians in each trial arm 2 months before and 6 months after dissemination of the PEMs. We used analysis of covariance to test for group differences using a 2 × 3 factorial design. We content-analysed an open-ended question about perceived barriers to thiazide prescription. Using control group data, we tested whether baseline measures of TPB constructs predicted self-reported thiazide prescribing at follow-up.



Four hundred twenty-six physicians completed pre- and post-intervention questionnaires. Baseline scores on measures of TPB constructs were high: intention mean = 5.9 out of 7 (SD = 1.4), attitude mean = 5.8 (SD = 1.1), subjective norm mean = 5.8 (SD = 1.1) and PBC mean = 6.2 (SD = 1.0). The arms did not significantly differ post-intervention on any of the theory-based constructs, suggesting a possible ceiling effect. Content analysis of perceived barriers suggested post-intentional barriers to prescribing thiazides most often focused on specific patient clinical characteristics and potential side effects. Baseline intention (β = 0.63, p < 0.01) but not PBC (β = 0.04, p = 0.78) predicted 42.6 % of the variance in self-reported behaviour at follow-up in the control group.



Congruent with the Ontario Printed Educational Messages trial results and aligned with the TPB, we saw no impact of the intervention on any TPB constructs. The theoretical basis of this evaluation suggests possible explanations for the failure of the PEM intervention to change professional behaviour, which can directly inform the design and content of future theory-based PEM interventions to change professional behaviour.



ISRCTN, Canada ISRCTN72772651.
Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, 501 Smyth Road, Box 201B, Ottawa, Ontario, K1H 8L6, Canada.|School of Epidemiology, Public Health and Preventive Medicine, 451 Smyth Road, Ottawa, Ontario, K1H 8M5, Canada.
Justin
J
Presseau
Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, 501 Smyth Road, Box 201B, Ottawa, Ontario, K1H 8L6, Canada. jgrimshaw@ohri.ca.|Department of Medicine, University of Ottawa, 451 Smyth Rd, Ottawa, Ontario, K1H 8M5, Canada. jgrimshaw@ohri.ca.
Jeremy M
JM
Grimshaw
Retired, Ottawa, Canada.
Jacqueline M
JM
Tetroe
Institute of Health and Society, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle Upon Tyne, NE2 4AX, England.
Martin P
MP
Eccles
School of Health Sciences, City University London, Northampton Square, London, EC1V 0HB, UK.
Jill J
JJ
Francis
Faculty of Nursing, Laval University, Pavillon Ferdinand-Vandry, 1050 Avenue de la Medicine, Room 1445, Quebec City, Quebec, G1V 0A6, Canada.
Gaston
G
Godin
Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, 501 Smyth Road, Box 201B, Ottawa, Ontario, K1H 8L6, Canada.|School of Epidemiology, Public Health and Preventive Medicine, 451 Smyth Road, Ottawa, Ontario, K1H 8M5, Canada.|School of Nursing, Faculty of Health Sciences, University of Ottawa, 451 Smyth Rd, Ottawa, Ontario, K1H 8M5, Canada.
Ian D
ID
Graham
Canadian Diabetes Association, 522 University Ave, Toronto, ON, M5G 2A2, Canada.
Janet E
JE
Hux
Institute of Applied Health Sciences, College of Life Sciences and Medicine, 2nd floor, Health Sciences Building, Foresterhill, Aberdeen, AB25 2ZD, UK.
Marie
M
Johnston
Department of Family Medicine and Emergency Medicine, Université Laval, Québec City, Québec, G1K 7P4, Canada.
France
F
Légaré
School of Psychology, University of Ottawa, 120 University, Social Sciences Building FSS-5052, Ottawa, Ontario, K1N 6N5, Canada.
Louise
L
Lemyre
Ottawa Hospital Research Institute, The Ottawa Hospital, General Campus, 501 Smyth Road, Box 201B, Ottawa, Ontario, K1H 8L6, Canada.
Nicole
N
Robinson
Centre for Studies in Family Medicine, Department of Family Medicine, Schulich School of Medicine and Dentistry, Western University, 1465 Richmond Street, London, Ontario, N6A 3K7, Canada.|Institute for Clinical Evaluative Sciences, University of Toronto, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5, Canada.
Merrick
M
Zwarenstein
D005260:Female; D006801:Humans; D006973:Hypertension / Q000188:drug therapy*; D008297:Male; D009864:Ontario; D010174:Pamphlets; D058007:Physicians, Primary Care; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data*; D055656:Prescriptions / Q000706:statistics & numerical data*; D015397:Program Evaluation; D049993:Sodium Chloride Symporter Inhibitors / Q000627:therapeutic use*; D011795:Surveys and Questionnaires
D049993:Sodium Chloride Symporter Inhibitors