Some usages can include both of these factors. Subjective well-being (swb) includes measures of current experience (emotions, moods, and feelings) and of life satisfaction.[nb 1] For instance Sonja Lyubomirsky has described happiness as "the experience of joy, contentment, or positive well-being, combined with a sense that one's life is good, meaningful, and worthwhile."Eudaimonia, is a Greek term variously translated as happiness, welfare, flourishing, and blessedness. Xavier Landes has proposed that happiness include measures of subjective wellbeing, mood and eudaimonia.
These differing uses can give different results. For instance the correlation of income levels has been shown to be substantial with life satisfaction measures, but to be far weaker, at least above a certain threshold, with current experience measures. Whereas Nordic countries often score highest on swb surveys, South American countries score higher on affect-based surveys of current positive life experiencing.
People have been trying to measure happiness for centuries. In 1780, the English utilitarian philosopher Jeremy Bentham proposed that as happiness was the primary goal of humans it should be measured as a way of determining how well the government was performing.
Happiness economists are not overly concerned with philosophical and methodological issues and continue to use questionaries to measure average happiness of populations.
Several scales have been developed to measure happiness:
The Subjective Happiness Scale (SHS) is a four-item scale, measuring global subjective happiness from 1999. The scale requires participants to use absolute ratings to characterize themselves as happy or unhappy individuals, as well as it asks to what extent they identify themselves with descriptions of happy and unhappy individuals.
The Positive and Negative Affect Schedule (PANAS) from 1988 is a 20-item questionnaire, using a five-point Likert scale (1 = very slightly or not at all, 5 = extremely) to assess the relation between personality traits and positive or negative affects at "this moment, today, the past few days, the past week, the past few weeks, the past year, and in general". A longer version with additional affect scales was published 1994.
The Satisfaction with Life Scale (SWLS) is a global cognitive assessment of life satisfaction developed by Ed Diener. A seven-point Likert scale is used to agree or disagree with five statements about one's life.
The Cantril ladder method has been used in the World Happiness Report. Respondents are asked to think of a ladder, with the best possible life for them being a 10, and the worst possible life being a 0. They are then asked to rate their own current lives on that 0 to 10 scale.
Positive Experience; the survey by Gallup asks if, the day before, people experienced enjoyment, laughing or smiling a lot, feeling well-rested, being treated with respect, learning or doing something interesting. 9 of the top 10 countries in 2018 were South American, led by Paraguay and Panama. Country scores range from 85 to 43.
Since 2012, a World Happiness Report has been published. Happiness is evaluated, as in "How happy are you with your life as a whole?", and in emotional reports, as in "How happy are you now?," and people seem able to use happiness as appropriate in these verbal contexts. Using these measures, the report identifies the countries with the highest levels of happiness. In subjective well-being measures, the primary distinction is between cognitive life evaluations and emotional reports.
Academic economists and international economic organizations are arguing for and developing multi-dimensional dashboards which combine subjective and objective indicators to provide a more direct and explicit assessment of human wellbeing. There are many different contributors to adult wellbeing, that happiness judgements partly reflect the presence of salient constraints, and fairness, autonomy, community and engagement are key aspects of happiness and wellbeing throughout the life course. Although these factors play a role in happiness, they do not all need to improve simultaneously to help one achieve an increase in happiness.
Happiness has been found to be quite stable over time.
Philosophy of happiness is often discussed in conjunction with ethics. Traditional European societies, inherited from the Greeks and from Christianity, often linked happiness with morality, which was concerned with the performance in a certain kind of role in a certain kind of social life.
Happiness remains a difficult term for moral philosophy. Throughout the history of moral philosophy, there has been an oscillation between attempts to define morality in terms of consequences leading to happiness and attempts to define morality in terms that have nothing to do with happiness at all.
Connections between happiness and morality have been studied in a variety of ways in psychology. Empirical research suggests that laypeople's judgments of a person's happiness in part depend on perceptions of that person's morality, suggesting that judgments of others' happiness involve moral evaluation. A large body of research also suggests that engaging in prosocial behavior can increase happiness.
Aristotle described eudaimonia (Greek: εὐδαιμονία) as the goal of human thought and action. Eudaimonia is often translated to mean happiness, but some scholars contend that "human flourishing" may be a more accurate translation. Aristotle's use of the term in Nicomachiean Ethics extends beyond the general sense of happiness.
In the Nicomachean Ethics, written in 350 BCE, Aristotle stated that happiness (also being well and doing well) is the only thing that humans desire for their own sake, unlike riches, honour, health or friendship. He observed that men sought riches, or honour, or health not only for their own sake but also in order to be happy. For Aristotle the term eudaimonia, which is translated as 'happiness' or 'flourishing' is an activity rather than an emotion or a state. Eudaimonia (Greek: εὐδαιμονία) is a classical Greek word consists of the word "eu" ("good" or "well-being") and "daimōn" ("spirit" or "minor deity", used by extension to mean one's lot or fortune). Thus understood, the happy life is the good life, that is, a life in which a person fulfills human nature in an excellent way.
Specifically, Aristotle argued that the good life is the life of excellent rational activity. He arrived at this claim with the "Function Argument". Basically, if it is right, every living thing has a function, that which it uniquely does. For Aristotle human function is to reason, since it is that alone which humans uniquely do. And performing one's function well, or excellently, is good. According to Aristotle, the life of excellent rational activity is the happy life. Aristotle argued a second-best life for those incapable of excellent rational activity was the life of moral virtue.
The key question Aristotle seeks to answer is "What is the ultimate purpose of human existence?" A lot of people are seeking pleasure, health, and a good reputation. It is true that those have a value, but none of them can occupy the place of the greatest good for which humanity aims. It may seem like all goods are a means to obtain happiness, but Aristotle said that happiness is always an end in itself.
Friedrich Nietzsche critiqued the English Utilitarians' focus on attaining the greatest happiness, stating that "Man does not strive for happiness, only the Englishman does". Nietzsche meant that making happiness one's ultimate goal and the aim of one's existence, in his words "makes one contemptible." Nietzsche instead yearned for a culture that would set higher, more difficult goals than "mere happiness." He introduced the quasi-dystopic figure of the "last man" as a kind of thought experiment against the utilitarians and happiness-seekers.
These small, "last men" who seek after only their own pleasure and health, avoiding all danger, exertion, difficulty, challenge, struggle are meant to seem contemptible to Nietzsche's reader. Nietzsche instead wants us to consider the value of what is difficult, what can only be earned through struggle, difficulty, pain and thus to come to see the affirmative value suffering and unhappiness truly play in creating everything of great worth in life, including all the highest achievements of human culture, not least of all philosophy.
Theories on how to achieve happiness include "encountering unexpected positive events", "seeing a significant other", and "basking in the acceptance and praise of others".
Some others believe that happiness is not solely derived from external, momentary pleasures.
Research on positive psychology, well-being, eudaimonia and happiness, and the theories of Diener, Ryff, Keyes, and Seligmann covers a broad range of levels and topics, including "the biological, personal, relational, institutional, cultural, and global dimensions of life." The psychiatrist George Vaillant and the director of longitudinal Study of Adult Development at Harvard UniversityRobert J. Waldinger found that those who were happiest and healthier reported strong interpersonal relationships. Research showed that adequate sleep contributes to well-being. Good mental health and good relationships contribute more than income to happiness. In 2018, Laurie R. Santos course titled "Psychology and the Good Life" became the most popular course in the history of Yale University and was made available for free online to non-Yale students.
Some commentators focus on the difference between the hedonistic tradition of seeking pleasant and avoiding unpleasant experiences, and the eudaimonic tradition of living life in a full and deeply satisfying way. Kahneman has said that "“When you look at what people want for themselves, how they pursue their goals, they seem more driven by the search for satisfaction than the search for happiness.”
Woman kissing a baby on the cheek
Maslow's hierarchy of needs is a pyramid depicting the levels of human needs, psychological, and physical. When a human being ascends the steps of the pyramid, self-actualization is reached. Beyond the routine of needs fulfillment, Maslow envisioned moments of extraordinary experience, known as peak experiences, profound moments of love, understanding, happiness, or rapture, during which a person feels more whole, alive, self-sufficient, and yet a part of the world. This is similar to the flow concept of Mihály Csíkszentmihályi. The concept of flow is the idea that after our basic needs are met we can achieve greater happiness by altering our consciousness by becoming so engaged in a task that we lose our sense of time. Our intense focus causes us to forget any other issues, which in return promotes positive emotions.
Erich Fromm said "Happiness is the indication that man has found the answer to the problem of human existence: the productive realization of his potentialities and thus, simultaneously, being one with the world and preserving the integrity of his self. In spending his energy productively he increases his powers, he „burns without being consumed.""
Ronald Inglehart has traced cross-national differences in the level of happiness based on data from the World Values Survey. He finds that the extent to which a society allows free choice has a major impact on happiness. When basic needs are satisfied, the degree of happiness depends on economic and cultural factors that enable free choice in how people live their lives. Happiness also depends on religion in countries where free choice is constrained.
Sigmund Freud said that all humans strive after happiness, but that the possibilities of achieving it are restricted because we "are so made that we can derive intense enjoyment only from a contrast and very little from the state of things."
Since 2000 the field of positive psychology has expanded drastically in terms of scientific publications, and has produced many different views on causes of happiness, and on factors that correlate with happiness. Numerous short-term self-help interventions have been developed and demonstrated to improve happiness.
Various writers, including Camus and Tolle, have written that the act of searching or seeking for happiness is incompatible with being happy.
John Stuart Mill believed that for the great majority of people happiness is best achieved en passant, rather than striving for it directly. This meant no self-consciousness, scrutiny, self-interrogation, dwelling on, thinking about,
imagining or questioning on one's happiness. Then, if otherwise fortunately circumstanced, one would "inhale happiness with the air you breathe."
William Inge said that "on the whole, the happiest people seem to be those who have no particular cause for being happy except the fact that they are so."Orison Swett Marden said that "some people are born happy."
Cognitive behavioral therapy
Cognitive behavioral therapy is a popular therapeutic method used to change habits by merely changing thoughts. It focuses on emotional regulation and uses a lot of positive psychology practices. It is often used for people with depression or anxiety, and works towards how to lead a happier life.
There is a wealth of cross-sectional studies on happiness and physical health that shows consistent positive relationships. Follow-up studies appear to show that happiness does not predict longevity in sick populations, but that it does predict longevity among healthy populations.
Low mood is correlated with many negative life outcomes such as suicide, poor health, substance abuse, and low life expectancy. By extension, happiness protects from those negative outcomes.
This section needs expansion. You can help by adding to it. (September 2022)
June Gruber argued that happiness may trigger a person to be more sensitive, more gullible, less successful, and more likely to undertake high risk behaviours. She also conducted studies suggesting that seeking happiness can have negative effects, such as failure to meet over-high expectations.Iris Mauss has shown that the more people strive for happiness, the more likely they will set up too high of standards and feel disappointed. One study shows that women who value happiness more tend to react less positively to happy emotions. A 2012 study found that psychological well-being was higher for people who experienced both positive and negative emotions.
Society and culture
Newly commissioned officers celebrate their new positions by throwing their midshipmen covers into the air as part of the U.S. Naval Academy class of 2011 graduation and commissioning ceremony.
Richer nations tend to have higher measures of happiness than poorer nations. The relationship between wealth and happiness is not linear and the same GDP increase in poor countries will have more effect on happiness than in wealthy countries.
Some political scientists argue that life satisfaction is positively related to the social democratic model of a generous social safety net, pro-worker labor market regulations, and strong labor unions. Others argue that happiness is strongly correlated with economic freedom, preferably within the context of a western mixed economy, with free press and a democracy.
One theory is that higher SWB in richer countries is related to their more individualistic cultures. Individualistic cultures may satisfy intrinsic motivations to a higher degree that collectivistic cultures, and fulfilling intrinsic motivations, as opposed to extrinsic motivations, may relate to greater levels of happiness, leading to more happiness in individualistic cultures.
Cultural views on happiness have changed over time. For instance Western concern about childhood being a time of happiness has occurred only since the 19th century. Not all cultures seek to maximize happiness,[nb 2][nb 3] and some cultures are averse to happiness. It has been found in Western cultures that individual happiness is the most important. Some other cultures have opposite views and tend to be aversive to the idea of individual happiness. For example, people living in Eastern Asian cultures focus more on the need for happiness within relationships with others and even find personal happiness to be harmful to fulfilling happy social relationships.[nb 2][nb 3]
The Chinese Confucian thinker Mencius, who had sought to give advice to ruthless political leaders during China's Warring States period, was convinced that the mind played a mediating role between the "lesser self" (the physiological self) and the "greater self" (the moral self), and that getting the priorities right between these two would lead to sage-hood. He argued that if one did not feel satisfaction or pleasure in nourishing one's "vital force" with "righteous deeds", then that force would shrivel up (Mencius, 6A:15 2A:2). More specifically, he mentions the experience of intoxicating joy if one celebrates the practice of the great virtues, especially through music.
Happiness or simcha (Hebrew: שמחה) in Judaism is considered an important element in the service of God. The biblical verse "worship The Lord with gladness; come before him with joyful songs," (Psalm 100:2) stresses joy in the service of God. A popular teaching by Rabbi Nachman of Breslov, a 19th-century Chassidic Rabbi, is "Mitzvah Gedolah Le'hiyot Besimcha Tamid," it is a great mitzvah (commandment) to always be in a state of happiness. When a person is happy they are much more capable of serving God and going about their daily activities than when depressed or upset.[self-published source?]
According to Augustine of Hippo and Thomas Aquinas, man's last end is happiness: "all men agree in desiring the last end, which is happiness." Aquinas agreed with Aristotle that happiness cannot be reached solely through reasoning about consequences of acts, but also requires a pursuit of good causes for acts, such as habits according to virtue.
According to Aquinas, happiness consists in an "operation of the speculative intellect": "Consequently happiness consists principally in such an operation, viz. in the contemplation of Divine things." And, "the last end cannot consist in the active life, which pertains to the practical intellect." So: "Therefore the last and perfect happiness, which we await in the life to come, consists entirely in contemplation. But imperfect happiness, such as can be had here, consists first and principally in contemplation, but secondarily, in an operation of the practical intellect directing human actions and passions."
Human complexities, like reason and cognition, can produce well-being or happiness, but such form is limited and transitory. In temporal life, the contemplation of God, the infinitely Beautiful, is the supreme delight of the will. Beatitudo, or perfect happiness, as complete well-being, is to be attained not in this life, but the next.
As of 2016[update], no evidence of happiness causing improved physical health has been found; the topic is being researched at the Lee Kum Sheung Center for Health and Happiness at the Harvard T.H. Chan School of Public Health.
A positive relationship has been suggested between the volume of the brain's gray matter in the right precuneus area and one's subjective happiness score.
Sonja Lyubomirsky has estimated that 50 percent of a given human's happiness level could be genetically determined, 10 percent is affected by life circumstances and situation, and a remaining 40 percent of happiness is subject to self-control.
When discussing genetics and their effects on individuals it is important to first understand that genetics do not predict behavior. It is possible for genes to increase the likelihood of individuals being happier compared to others, but they do not 100 percent predict behavior.
At this point in scientific research, it has been hard to find a lot of evidence to support this idea that happiness is affected in some way by genetics. In a 2016 study, Michael Minkov and Michael Harris Bond found that a gene by the name of SLC6A4 was not a good predictor of happiness level in humans.
On the other hand, there have been many studies that have found genetics to be a key part in predicting and understanding happiness in humans. In a review article discussing many studies on genetics and happiness, they discussed the common findings. The author found an important factor that has affected scientist findings this being how happiness is measured. For example, in certain studies when subjective wellbeing is measured as a trait heredity is found to be higher, about 70 to 90 percent. In another study, 11,500 unrelated genotypes were studied, and the conclusion was the heritability was only 12 to 18 percent. Overall, this article found the common percent of heredity was about 20 to 50 percent.
^"How Universal is Happiness?" Ruut Veenhoven, Chapter 11 in Ed Diener, John F. Helliwell & Daniel Kahneman (Eds.) International Differences in Well-Being, 2010, Oxford University Press, New York, ISBN978-0199732739
^Graham, Michael C. (2014). Facts of Life: ten issues of contentment. Outskirts Press. pp. 6–10. ISBN978-1478722595.
^https://plato.stanford.edu/entries/happiness/Archived 11 June 2018 at the Wayback Machine 2011, "'Happiness' is often used, in ordinary life, to refer to a short-lived state of a person, frequently a feeling of contentment: 'You look happy today'; 'I'm very happy for you'. Philosophically, its scope is more often wider, encompassing a whole life. And in philosophy it is possible to speak of the happiness of a person's life, or of their happy life, even if that person was in fact usually pretty miserable. The point is that some good things in their life made it a happy one, even though they lacked contentment. But this usage is uncommon, and may cause confusion.' https://plato.stanford.edu/entries/well-being/Archived 25 October 2018 at the Wayback Machine 2017
^Kashdan, Todd B.; Biswas-Diener, Robert; King, Laura A. (October 2008). "Reconsidering happiness: the costs of distinguishing between hedonics and eudaimonia". The Journal of Positive Psychology. 3 (4): 219–233. doi:10.1080/17439760802303044. S2CID17056199.
^"Surveying large numbers of Americans in one case, and what is claimed to be the first globally representative sample of humanity in the other, these studies found that income does indeed correlate substantially (.44 in the global sample), at all levels, with life satisfaction – strictly speaking, a "life evaluation" measure that asks respondents to rate their lives without saying whether they are satisfied. Yet the correlation of household income with the affect measures is far weaker: globally, .17 for positive affect, -.09 for negative affect; and in the United States, essentially zero above $75,000 (though quite strong at low income levels). If the results hold up, the upshot appears to be that income is pretty strongly related to life satisfaction, but weakly related to emotional well-being, at least above a certain threshold." Section 3.3, Happiness, Stanford Encyclopedia of Philosophy, https://plato.stanford.edu/entries/happiness/#HedVerEmoStaArchived 2018-06-11 at the Wayback Machine
^"High income improves evaluation of life but not emotional well-being", Daniel Kahneman and Angus Deaton, Proceedings of the National Academy of Sciences, 21/9/10
^Helliwell, John; Yang, Shun (2012). World Happiness Report 2012 (Report). p. 11. Archived from the original on 18 July 2016. How does happiness come into this classification? For better or worse, it enters in three ways. It is sometimes used as a current emotional report – "How happy are you now?," sometimes as a remembered emotion, as in "How happy were you yesterday?," and very often as a form of life evaluation, as in "How happy are you with your life as a whole these days?" People answer these three types of happiness question differently, so it is important to keep track of what is being asked. The good news is that the answers differ in ways that suggest that people understand what they are being asked, and answer appropriately
^Inge, W.R. (1926). Lay Thoughts of a Dean. Creative Media Partners, LLC. ISBN978-1379053095. Looking back, I think I can separate the years when I was happy and those when I was unhappy. But perhaps at the time I should have judged differently.
^Helliwell, John; et al. World Happiness Report 2015 (Report). Some have argued that it is misleading to use 'happiness' as a generic term to cover subjective well-being more generally. While 'subjective well-being' is more precise, it simply does not have the convening power of 'happiness'. The main linguistic argument for using happiness in a broader generic role is that happiness plays two important roles within the science of well-being, appearing once as a prototypical positive emotion and again as part of a cognitive life evaluation question. This double use has sometimes been used to argue that there is no coherent structure to happiness responses. The converse argument made in the World Happiness Reports is that this double usage helps to justify using happiness in a generic role, as long as the alternative meanings are clearly understood and credibly related. Evidence from a growing number of large scale surveys shows that the answers to questions asking about the emotion of happiness differ from answers to judgmental questions asking about a person's happiness with life as a whole in exactly the ways that theory would suggest. Answers to questions about the emotion of happiness relate well to what is happening at the moment. Evaluative answers, in response to questions about life as a whole, are supported by positive emotions, as noted above, but also driven much more, than are answers to questions about emotions, by a variety of life circumstances, including income, health and social trust. quoted in Helliwell, John F. (25 February 2017). "What's Special About Happiness as a Social Indicator?". Social Indicators Research. Springer Science and Business Media LLC. 135 (3): 965–968. doi:10.1007/s11205-017-1549-9. ISSN0303-8300. S2CID151828351.
^Watson, David; Clark, Lee A.; Tellegen, Auke (1988). "Development and validation of brief measures of positive and negative affect: The PANAS scales". Journal of Personality and Social Psychology. 54 (6): 1063–1070. doi:10.1037/0022-35220.127.116.113. PMID3397865. S2CID7679194.
^Watson, David; Clark, Lee Anna (1994), The PANAS-X: Manual for the Positive and Negative Affect Schedule – Expanded Form, The University of Iowa, doi:10.17077/48vt-m4t2
^ abLevin, K. A.; Currie, C. (November 2014). "Reliability and Validity of an Adapted Version of the Cantril Ladder for Use with Adolescent Samples". Social Indicators Research. 119 (2): 1047–1063. doi:10.1007/s11205-013-0507-4. S2CID144584204.
^"FAQ". Archived from the original on 31 December 2018. Retrieved 27 January 2019.
^Baumeister, Roy F.; Vohs, Kathleen D.; Aaker, Jennifer L.; Garbinsky, Emily N. (November 2013). "Some key differences between a happy life and a meaningful life". The Journal of Positive Psychology. 8 (6): 505–516. doi:10.1080/17439760.2013.830764. S2CID11271686.
^Costa, Paul T.; McCrae, Robert R.; Zonderman, Alan B. (August 1987). "Environmental and dispositional influences on well-being: Longitudinal follow-up of an American national sample". British Journal of Psychology. 78 (3): 299–306. doi:10.1111/j.2044-8295.1987.tb02248.x. PMID3620790.
^Aknin, Lara B.; Whillans, Ashley V. (January 2021). "Helping and Happiness: A Review and Guide for Public Policy". Social Issues and Policy Review. 15 (1): 3–34. doi:10.1111/sipr.12069. S2CID225505120.
^Hui, Bryant P. H.; Ng, Jacky C. K.; Berzaghi, Erica; Cunningham-Amos, Lauren A.; Kogan, Aleksandr (December 2020). "Rewards of kindness? A meta-analysis of the link between prosociality and well-being". Psychological Bulletin. 146 (12): 1084–1116. doi:10.1037/bul0000298. PMID32881540. S2CID221497259.
^"You will never be happy if you continue to search for what happiness consists of. You will never live if you are looking for the meaning of life." Albert Camus, in "Intuitions" (October 1932), published in Youthful Writings (1976)
^"Don't Seek Happiness. If you seek it, you won't find it, because seeking is the antithesis of happiness" Eckhart Tolle, A New Earth: Awakening to Your Life's Purpose
^"Wealth, like happiness, is never attained when sought after directly. It comes as a by-product of providing a useful service." Henry Ford
^Frank Crane wrote that "nobody who pursued happiness ever found it" (Adventures in Common Sense, 1920, p49)
^"The enjoyments of life (such was now my theory) are sufficient to make it a pleasant thing, when they are taken en passant, without being made a principal object. Once make them so, and they are immediately felt to be insufficient. They will not bear a scrutinizing examination. Ask yourself whether you are happy, and you cease to be so. The only chance is to treat, not happiness, but some end external to it, as the purpose of life. Let your self-consciousness, your scrutiny, your self-interrogation, exhaust themselves on that; and if otherwise fortunately circumstanced you will inhale happiness with the air you breathe, without dwelling on it or thinking about it, without either forestalling it in imagination, or putting it to flight by fatal questioning. This theory now became the basis of my philosophy of life. And I still hold to it as the best theory for all those who have but a moderate degree of sensibility and of capacity for enjoyment; that is, for the great majority of mankind." Autobiography, Ch 5, https://www.gutenberg.org/files/10378/10378-h/10378-h.htm#link2H_NOTEhttps://www.laits.utexas.edu/poltheory/mill/auto/auto.c05.html
^Essay entitled 'Happy People', dated 1921, included in Inge, W.R. (1926). Lay Thoughts of a Dean. Garden City Publishing Company. p. 211.
^"Some people are born happy. No matter what their circumstances are they are joyous, content and satisfied with everything. They carry a perpetual holiday in their eye and see joy and beauty everywhere. When we meet them they impress us as just having met with some good luck, or that they have some good news to tell you. Like the bees that extract honey from every flower, they have a happy alchemy which transmutes even gloom into sunshine." How To Succeed, (1896) https://www.gutenberg.org/files/20513/20513-h/20513-h.htm
^See also this collection of full-text peer reviewed scholarly articles on this subject by Radcliff and colleagues (from "Social Forces," "The Journal of Politics," and "Perspectives on Politics," among others) Archived 12 July 2015 at the Wayback Machine
^Joshanloo, Mohsen; Jarden, Aaron (1 May 2016). "Individualism as the moderator of the relationship between hedonism and happiness: A study in 19 nations". Personality and Individual Differences. 94: 149–152. doi:10.1016/j.paid.2016.01.025.