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Student: Abby Zarifeh
Supervisors: Dr Ben Hudson, Lorraine Young
Sponsor: Pegasus Health


Prevention and early diagnosis of disease are important aspects of general practice. A range of medications and screening tests may be used for this. The aim of this type of healthcare is to reduce the number of cases of disease or reduce the risk of dying of the disease. Many of these types of treatments are effective, but the chance of any one person benefiting from them is usually small. When deciding whether to take a preventive treatment or take part in screening, it is important that patients are aware of the likelihood that they will benefit from doing so. There is little information available on patients' understanding of how effective preventive interventions truly are. There is also little known about the levels of effectiveness that patients believe would justify participation in interventions with their costs, risks and inconveniences.


The aims for this project were:

  1. To investigate public perceptions of the expected effect of preventive interventions
  2. To investigate the minimum levels of acceptable effectiveness of preventive interventions


We designed a questionnaire to assess patients' expectations of four commonly used preventive interventions in general practice. The interventions included were:

  • x-ray screening for breast cancer (mammography)
  • screening tests for bowel cancer
  • medications to decrease the likelihood of broken hips in people with osteoporosis
  • medications to decrease the likelihood of cardiovascular disease (disease of the heart and/or blood vessels) occurring in people from the general population

Patients aged 50-70 years were selected from several Christchurch general practitioners' lists. This age group was chosen as the preventive interventions illustrated in the survey are largely aimed at those of this age. Participants were asked to indicate the number of deaths or hip fractures they expected would be prevented due to the preventive intervention for a group of 5000 people from the general population treated or screened for 10 years. Participants were also asked to indicate how many lives out of 5000 people from the general population over 10 years they thought should be saved, or hip fractures prevented, to justify the costs, risks and inconveniences of the preventive intervention.


977 patients were mailed the questionnaire. A total of 323 questionnaires were returned and responses were entered into a database. The average age of participation was 59.5 years with 89% of respondents identifying their ethnicity as New Zealand European and 2.8% as Māori.

Most participants significantly overestimated the number of deaths or fractures that would be prevented by the interventions. For each of the four interventions, over half the respondents expected 500 or more deaths (or fractures) would be prevented. For example over 60% of participants indicated they would expect 500 or more deaths to be prevented out of 5000 women due to screening for breast cancer with mammography. The actual number of deaths prevented based on international evidence is approximately 2.5 deaths out of 5000 women over a ten year period.

The range of responses was wider for the questions looking at what number of lives participants thought should be saved or hip fractures prevented to justify costs, risks and inconveniences of the preventive intervention. However, the majority of participants still gave high estimates of deaths or fractures prevented for these questions.


This study found that participants generally overestimated the benefits of the examples of preventive healthcare we asked about. We also found that many participants would still think the treatments and screening worthwhile even if they prevent a smaller number of deaths or fractures than is believed to be the case. This may mean that respondents believe that even a small degree of benefit means that an intervention is worth undertaking.

There are many possible reasons for these findings, but we feel that this information will be useful for healthcare workers to consider when discussing this type of care with patients. We hope that this will help patients to make better informed decisions about whether to use preventive medicines or take part in screening programmes.

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