Adherence is a multidimensional phenomenon determined by the interplay of five sets of factors, here termed "dimensions", of which patient-related factors are just one determinant (Figure 3).The common belief that patients are solely responsible for taking their treatment is misleading and most often reflects a misunderstanding of how other factors affect people's behaviour and capacity to adhere to their treatment.
The five dimensions are briefly discussed below. The length of the discussion on each dimension reflects the quantity of evidence available, which is biased by the traditional misconception that adherence is a patient-driven problem. Therefore, the size of the section does not reflect its importance.
Figure 3 The five dimensions of adherence
HCT, Health-care team
A. Social and economic factors
Although socioeconomic status has not consistently been found to be an independent predictor of adherence, in developing countries low socioeconomic status may put patients in the position of having to choose between competing priorities. Such priorities frequently include demands to direct the limited resources available to meet the needs of other family members, such as children or parents for whom they care.
Some factors reported to have a significant effect on adherence are: poor socioeconomic status, poverty, illiteracy, low level of education, unemployment, lack of effective social support networks, unstable living conditions, long distance from treatment centre, high cost of transport, high cost of medication, changing environmental situations, culture and lay beliefs about illness and treatment, and family dysfunction. Various sociodemographic and economic variables are discussed in the course of this report (see also Annex 3).
Some studies have reported that organizational factors are more related to adherence than sociodemographic ones, but this might differ from one setting to another. An interesting study by Albaz in Saudi Arabia concluded that organizational variables (time spent with the doctor, continuity of care by the doctor, communication style of the doctor and interpersonal style of the doctor) are far more important than sociodemographic variables (gender, marital status, age, educational level and health status) in affecting patients' adherence (1).
Race has frequently been reported to be a predictor of adherence, regardless of whether the members of a particular race are living in their country of origin or elsewhere as immigrants. Often, cultural beliefs are the reason behind these racial differences (2), but, no less often, social inequalities confound these findings (3). For example, in the United Kingdom, HIV-positive black Africans have been found to have a different experience of treatment because of their fear of being experimented on, distrust of the medical profession and fears of discrimination (4). In the United States, African Americans have been reported to express significantly more doubt regarding their ability to use protease inhibitors and adhere to the treatment, and about the competence of their physicians than do the white population (5).
War has also been reported to have an influence on adherence to therapies, even after the war is over. This is mainly the result of war experiences such as economic hardship, lack of medical control, fatalism and anarchy (6).
Age is a factor reported as affecting adherence, but inconsistently. It should be evaluated separately for each condition, and, if possible, by the characteristics of the patient and by developmental age group (i.e. children dependent on parent, adolescents, adults and elderly patients).
Adherence to treatment by children and adolescents ranges from 43% to 100%, with an average of 58% in developed countries (7). Several studies have suggested that adolescents are less adherent than younger children (8).The adherence of infants and toddlers to recommended treatment regimens is largely determined by the ability of the parent or guardian to understand and follow through with the recommended management. As age increases, children have the cognitive ability to carry out treatment tasks, but continue to need parental supervision.
School-aged children engage in the developmental task of industry, learning to regulate their own behaviour and control the world around them. As children enter school, they spend less time at home with their parents and are increasingly influenced by their peers and the social environment.
At the same time, increasing numbers of single and working parents have shifted more of the responsibility for disease management to the child. Assigning too much responsibility to a child for management of his or her treatment can lead to poor adherence. For example, studies indicate that, like adults, children exaggerate their adherence behaviours in their self-reports (9). Parents need to understand that inaccurate diary reporting may hinder appropriate disease management by clinicians. These findings underscore the value of parental supervision and guidance of children in their health behaviours. Shared family responsibility for treatment tasks and continuous reinforcement appear to be important factors in the enhancement of adherence to prescribed treatment for the paediatric population. In addition to parental supervision, behavioural techniques designed to help children, such as goal-setting, cueing, and rewards or tokens, have been found to improve adherence in the school-aged population (10).
Adolescents, though capable of greater autonomy in following treatment recommendations, struggle with self-esteem, body image, social role definition and peer-related issues. Poor adherence in adolescents may reflect rebellion against the regimen's control over their lives. Most studies indicate that children and adolescents who assume early sole responsibility for their treatment regimen are less adherent and in poorer control of their disease management. Both sustaining parental involvement and minimizing conflict between adolescents and their parents are valuable in encouraging adherence to treatment regimens. Providing families with information on forming a partnership between the parent(s) and the adolescent is of considerable importance in promoting adherence to treatment for this age group. Educational efforts focusing on adolescents' attitudes towards their disease and its management, instead of predominantly on knowledge acquisition, may be beneficial.
Elderly people represent 6.4 % of the world's population and their numbers are increasing by 800 000 every month. They have become the fastest-growing segment of the population in many developing countries (11,12).
This demographic transition has led to an increased prevalence of chronic illnesses that are particularly common in the elderly. These include Alzheimer disease, Parkinson disease, depression, diabetes, congestive heart failure, coronary artery disease, glaucoma, osteoarthritis, osteoporosis and others.
Many elderly patients present with multiple chronic diseases, which require complex long-term treatment to prevent frailty and disability. Furthermore, the elderly are the greatest consumers of prescription drugs. In developed countries, people over 60 years old consume approximately 50% of all prescription medicines (as much as three times more per capita than the general population) and are responsible for 60% of medication-related costs even though they represent only 12% to 18% of the population in these countries (13).
Adherence to treatments is essential to the well-being of elderly patients, and is thus a critically important component of care. In the elderly, failure to adhere to medical recommendations and treatment has been found to increase the likelihood of therapeutic failure (14), and to be responsible for unnecessary complications, leading to increased spending on health care, as well as to disability and early death (15).
Poor adherence to prescribed regimens affects all age groups. However, the prevalence of cognitive and functional impairments in elderly patients (16) increases their risk of poor adherence. Multiple co-morbidities and complex medical regimens further compromise adherence. Age-related alterations in pharmacokinetics and pharmacodynamics make this population even more vulnerable to problems resulting from nonadherence.
B. Health care team and system-related factors
Relatively little research has been conducted on the effects of health care team and system-related factors on adherence. Whereas a good patient-provider relationship may improve adherence (17), there are many factors that have a negative effect. These include, poorly developed health services with inadequate or non-existent reimbursement by health insurance plans, poor medication distribution systems, lack of knowledge and training for health care providers on managing chronic diseases, overworked health care providers, lack of incentives and feedback on performance, short consultations, weak capacity of the system to educate patients and provide follow-up, inability to establish community support and self-management capacity, lack of knowledge on adherence and of effective interventions for improving it.
C. Condition-related factors
Condition-related factors represent particular illness-related demands faced by the patient. Some strong determinants of adherence are those related to the severity of symptoms, level of disability (physical, psychological, social and vocational), rate of progression and severity of the disease, and the availability of effective treatments. Their impact depends on how they influence patients' risk perception, the importance of following treatment, and the priority placed on adherence. Co-morbidities, such as depression (18) (in diabetes or HIV/AIDS), and drug and alcohol abuse, are important modifiers of adherence behaviour.
D. Therapy-related factors
There are many therapy-related factors that affect adherence. Most notable are those related to the complexity of the medical regimen, duration of treatment, previous treatment failures, frequent changes in treatment, the immediacy of beneficial effects, side-effects, and the availability of medical support to deal with them.
Unique characteristics of diseases and/or therapies do not outweigh the common factors affecting adherence, but rather modify their influence. Adherence interventions should be tailored to the needs of the patient in order to achieve maximum impact.
E. Patient-related factors
Patient-related factors represent the resources, knowledge, attitudes, beliefs, perceptions and expectations of the patient.
Patients' knowledge and beliefs about their illness, motivation to manage it, confidence (self-efficacy) in their ability to engage in illness-management behaviours, and expectations regarding the outcome of treatment and the consequences of poor adherence, interact in ways not yet fully understood to influence adherence behaviour.
Some of the patient-related factors reported to affect adherence are: forgetfulness; psychosocial stress; anxieties about possible adverse effects; low motivation; inadequate knowledge and skill in managing the disease symptoms and treatment; lack of self-perceived need for treatment; lack of perceived effect of treatment; negative beliefs regarding the efficacy of the treatment; misunderstanding and nonacceptance of the disease; disbelief in the diagnosis; lack of perception of the health risk related to the disease; misunderstanding of treatment instructions; lack of acceptance of monitoring; low treatment expectations; low attendance at follow-up, or at counselling, motivational, behavioural, or psychotherapy classes; hopelessness and negative feelings; frustration with health care providers; fear of dependence; anxiety over the complexity of the drug regimen, and feeling stigmatized by the disease.
Perceptions of personal need for medication are influenced by symptoms, expectations and experiences and by illness cognitions (19). Concerns about medication typically arise from beliefs about side-effects and disruption of lifestyle, and from more abstract worries about the long-term effects and dependence. They are related to negative views about medicines as a whole and suspicions that doctors over-prescribe medicines (20,21) as well as to a broader "world view" characterized by suspicions of chemicals in food and the environment (22) and of science, medicine and technology (23).
A patient's motivation to adhere to prescribed treatment is influenced by the value that he or she places on following the regimen (cost-benefit ratio) and the degree of confidence in being able to follow it (24). Building on a patient's intrinsic motivation by increasing the perceived importance of adherence, and strengthening confidence by building self-management skills, are behavioural treatment targets that must be addressed concurrently with biomedical ones if overall adherence is to be improved.