On this page you can read about depression before and after COVID-19. You can also
read about how depression is defined clinically, with some philosophical considerations on definitions.
Corona and Depression
The situation before COVID-19
In late 2015, a document called Sygdomsbyrden I Danmark (Eng.: The Burden of Disease in Denmark) was published.  In the document, the prevalence, extent, and impact of various diseases on Denmark, including unipolar depression, were described. It is estimated that there are 11.000 new cases of unipolar depression each year, with 91.214 already suffering from relatively severe unipolar depression in 2015, and that unipolar depression each year costs about 1.2 billion DKK (~192 million USD) in treatment and care, while the cost due to unipolar depression caused production loss is about 3.1 billion DKK (~490 million USD) . The document also states that depression, both bipolar and unipolar, is one of the most common mental illnesses in Denmark. 
Up until 2019 about 91.000 Danes still suffered from unipolar depression and about 11.000 adult Danes were diagnosed with unipolar depression each year.  The numbers from 2019 are very similar to those from the 2015 report, and since no new report was made between 2015 and 2019, the same numbers were likely cited. If the numbers from 2019 are accurate, however, that means the number of people getting diagnosed with depression each year, about 11.000, is also the number of people either recovering from depression or dying with depression each year. Cases of unipolar depression in Denmark, the past few years before the COVID-19 pandemic, have either been the same or unknown. Besides, the occurrence of depression is believed to not have increased in the period between 2001 and 2011. 
The numbers from 2015 are only the documented cases of unipolar depression. Many people don’t see a doctor when they have depression. In 2005 it was estimated that 200.000 Danes suffered from depression and that only about half sought medical assistance . In 2013 the numbers were between 280.000 and 392.000.  The number of Danes suffering from depression has been increasing over the past decades, and the same trend can be observed globally as shown in figure 1.
Depression is an increasing problem, as more and more people are suffering from depression worldwide. However, with the occurrence of depression in Denmark between 2001 and 2011 not increasing, the same can be said globally. The number of people suffering from depression worldwide between 1990 and 2017 follows the growing global population (figure 2).
Using the underlying data for Figures 1 and 2, the estimated percentage of people suffering from depression worldwide goes from 3.2 % in 1990 to 3.5 % in 2017. An increase of 0.3 % over almost 30 years.
The situation during COVID-19
During the corona pandemic, Denmark had one of the highest-ranking incidences of depression and anxiety, which was contributed by the government closing the entire country due to high incidences of corona infection.
The corona lockdown did cause major concern for people in high-risk groups due to the closure of treatment facilities, creating barriers for people suffering from depression. The restrictions which lowered social events, working from home, and homeschooling had a big impact on loneliness, anxiety, and depression in general.
A study called The depressive state of Denmark during the COVID-19 pandemic was made, where researched had participants answer a survey in which the questions were based on the WHO-5 well-being scale . The results of the study suggested that the psychological well-being of the general Danish population was affected negatively by the COVID-19 pandemic.  This trend can also be seen in the wider world as a recession in the economy and isolation during the outbreak of covid19 has affected individuals globally negatively. 4 out of 10 Adults in the US did report symptoms of depression during covid, compared to 1 in 10 pre-covid. 
The restriction of social and freedom of movement was halted during this period, which contributed to major cases of anti-social psychological strain in individuals.
Another negative impact contributed by covid were too vulnerable individuals especially children and young teenagers during the lockdown, who previously were exposed to abusive environments at home, which could potentially have long-term effects on their psychological behavior as a result of the lockdown. Furthermore, individuals who contracted covid19 during the pandemic were also at risk of developing depression. The exposure of covid19 may have psychologically impacted individuals to exert a fear of spreading the disease further to friends and family. This “exposure-segregation” by society may have led to the stigmatization of individuals, who contracted covid19 during the pandemic. 
What depression exactly is, depends on the context in which it is addressed. Certain criteria must be met to diagnose someone with depression. These are a part of the clinical definition of depression. It is also possible to talk about depression beyond these boundaries. The clinical definition was developed as a guideline to determine when a human being can be diagnosed with depression. But while the clinical definition might be a sufficient list of symptoms, it is not an exhaustive list. It is in this context that our team has looked at depression beyond the clinical definition. We have looked at it both clinically and philosophically.
Considerations on the definition of Depression
One way to look at depression is to divide it into a mood and a mood disorder, which is the distinction between feeling depressed and having depression. There is a discussion among philosophers on whether this distinction can be made; however, we will be using it in this context to explore the definition of depression.
As a mood, depression “is a state of low spirits, typically involving painful and low affect”. It is difficult to distinguish feeling depressed from other negative emotions. But as a mood, depression does involve some sort of negative evaluation of something in our lives. Whether it is life in general, a specific event or even our fundamental values, it will be the negative evaluation of it, which results in us feeling depressed. We can feel depressed concerning loss, rejection, failure, or hopelessness. But feeling depressed because something goes wrong in our lives is a natural response to a non-desired situation. So, while depression as a mood is certainly often unwanted, it should not necessarily be undesired because feeling this way is how we know we need to change something in our lives.
As a mood disorder, on the other hand, depression is pathological and needs appropriate attention. Because depression, as a mood disorder, is, in fact, a mental illness. Therefore, it needs to be treated - just as any physical disease would need to be. The pathology of depression lies typically in feeling depressed long-term, with consequences such as trouble concentrating, insomnia, loss or increase of appetite, lack of motivation etc. A lot of these symptoms are accounted for in the clinical definition of depression. However, there are states of health, which are far from ideal, but that are still not accounted for in the official criteria for depression as pathological. But what is precisely defined as a depression mood disorder, aside from the clinical definition, is (as many things in philosophy) not exactly clear. In fact, not even clinically can there be agreed upon precisely what defines depression. So; that is what we will explore here. There are currently two recognized standards for the clinical definition of depression: The DSM-IV and the ICD-11.
In 1952 the first edition of the DSM-IV was released and mainly contained the clinical definition of depression that we use today. In this regard, a decision had to be made: Where is the cut-off? How does one qualify for being diagnosed with depression? Although this decision can hardly be said to have been arbitrarily made, the line must be drawn somewhere. Since 1952 there have been four more editions of the DSM-IV, with the most recent one (fifth edition) being published in 2013. The line has been moved throughout the five editions, as a growing body of research made our understanding of depression more profound. We will not explore the definition of depression in the DSM-IV further since this is the work of the American Psychiatric Associations, which amplifies the risk of it being primarily limited to the American standards of mental health. Instead, we will turn to the ICD-11.
The ICD-11 is the International Classification of Diseases and is recognized as the global standard for diagnostic health information. It came out in 2019 as a revised version of the ICD-10. Depression is catalogued under “Mood disorders” in the ICD-11, listed under “Mental, behavioral or neurodevelopmental disorders”.
Depressive disorders are characterised by depressive mood (e.g., sad, irritable, empty)
or loss of pleasure accompanied by other cognitive, behavioural, or neurovegetative
symptoms that significantly affect the individual’s ability to function. A depressive disorder should not be
diagnosed in individuals who have ever experienced a manic, mixed or hypomanic episode, which would
indicate the presence of a bipolar disorder. 
The distinction made earlier on this page between depression as a mood and a mood disorder is now highly relevant and helpful to understand this categorization. The ICD-11 has, by cataloging depression under “Mood disorders”, defined depression as a mood disorder. However, there is a further division of depression in this classification. Specifically, depression has been divided into six branches:
1. Single episode depressive disorder
2. Recurrent depressive disorder
3. Dysthymic disorder
4. Mixed depressive and anxiety disorder
5. Other specified depressive disorders
6. Depressive disorders, unspecified.
While branch 2.-6. can primarily be categorized as mood disorders, if we are to consider the earlier distinction from mood, it seems worth exploring how to categorize branch 1.. It is not a repetitive mood long-term; it may not quite fit our earlier definition of depression as a mood disorder. To refresh our memory, the definition was: “The pathology of depression lies typically in feeling depressed long-term, with consequences such as trouble concentrating, insomnia, loss or increase of appetite, lack of motivation etc.”. The question now remains whether this definition is consistent with 1. single episode depressive disorder. However, to answer this question, it is necessary to look at the definition of these single episode disorders.
Single episode depressive disorder is characterised by the presence or history of one depressive episode when there is no
history of prior depressive episodes. A depressive episode is characterised by a period of depressed mood or diminished interest in activities
occurring most of the day, nearly every day during a period lasting at least two weeks accompanied by other symptoms such as difficulty
concentrating, feelings of worthlessness or excessive or inappropriate guilt, hopelessness, recurrent thoughts of death or suicide,
changes in appetite or sleep, psychomotor agitation or retardation, and reduced energy or fatigue. 
The main points from this definition relevant to this discussion are that (a) single episode depressive disorders can only happen once to be defined as such, and (b) the episode must have lasted a minimum of two weeks. As far as (a) goes, the recurrence of a feeling overall defines a mood as a mood disorder. Of course, all sorts of moods are reoccurring, but if the mood is a specific negative one of the kinds, the reoccurrence of it will, after a certain point, be defined as a disorder. This is where (b) comes in because this definition of depression states that a depressive mood must be reoccurring most days for at least two weeks. The ICD-11 has then (roughly) decided that depression is not a disorder before it has been a mood for a significant part of two weeks or longer.
This is the official international line drawn between depression as “a state of low spirits, typically involving painful and low affect”, and depression as a pathological disorder, i.e., a mental illness. So, two weeks of being in a state of low spirits “accompanied by other symptoms such as difficulty concentrating, feelings of worthlessness or excessive or inappropriate guilt, hopelessness, recurrent thoughts of death or suicide, changes in appetite or sleep, psychomotor agitation or retardation, and reduced energy or fatigue” is then what is sufficient to be diagnosed with depression as a mental illness. Clinically speaking, anything less than this is simply a mood, and anything more is a disorder. As the ICD-11 has undergone a systematic revision “of scientific, clinical and public health evidence relevant to classification”, it is not our place to state that this definition of depression is wrong. We are not doctors or scientists, and it is a vast body of work from doctors and scientists who stand behind the ICD-11 classifications.
However, we can identify what sort of definition the ICD-11 standard of depression is. Philosophically speaking, one can distinguish between different definitions, e.g., real/nominal, dictionary, stipulative, descriptive, explicative and ostensive definitions. Definitions vary according to what is being defined and according to the goal and function of the definition. Furthermore, in philosophy, definitions have since the time of Immanuel Kant served an additional purpose. Namely, “to serve a highly distinctive role: that of solving epistemological problems”. Epistemology is the study of knowledge, and in this context, our epistemological concern is how to know the true nature of depression. Defining depression accurately is one way to begin to embrace this concern. The ICD-11 has undertaken this task, with what we identify as a real definition, which is the definition that is found when investigating “the thing or things denoted by X” (X being depression as a mood). To rephrase, the ICD-11´s definition of depression is philosophically an actual definition because it explores the sufficient criteria for the mood disorder depression. Beyond the classification as a true definition, the ICD-11´s definition can also be looked at from a descriptive viewpoint. Descriptive definitions, which the definition of depression also falls under, are distinguished from one another in three grades of descriptive adequacy: extensional, intensional, and sense:
A definition is extensionally adequate iff there are
no actual counterexamples to it; it is intensionally adequate
iff there are no possible counterexamples to it; and it is sense
adequate (or analytic) iff it endows the defined term with the right sense 
Descriptive definitions attend to spell out meaning, and at the same time, be adequate to the current usage of the word. The ICD-11´s definition of depression seems to be extensionally adequate and possibly sense adequate. However, it does not fit the description of intentional adequacy, since this degree of adequacy rules out the option that counterexamples exist to the definition of depression. It seems that ruling out the possibility of discovering new aspects of depression that might contradict the current one is a bit of a stretch at this point. The ICD has been revised 11 times and will most likely continue to be edited, with a growing body of research on mental illnesses.
The ICD-11 has defined the mood disorder depression as a mental illness that “are characterised by depressive mood (e.g., sad, irritable, empty) or loss of pleasure accompanied by other cognitive, behavioral, or neurovegetative symptoms that significantly affect the individual’s ability to function.” Furthermore, a good list of symptoms is completed when looking at the ICD´s first identified branch of depression (single episode depressive disorder). Here it is stated that to be diagnosed with depression as a mood disorder; it is required that the symptoms of depression have been “occurring most of the day, nearly every day during a period lasting at least two weeks”. Anything less than this will, by ICD-11 standards, be classified as a depressive mood. This definition of depression can philosophically be identified as an actual definition, which means that it explores the sufficient criteria for the mood disorder depression. Furthermore, this definition can also be categorized as a descriptive definition, as it undertakes to spell out meaning while trying to be adequate to the existing usage of the word, i.e., identifying the sufficient criteria for depressive mood disorder and recognizing that anything less than this is simply a depressive mood.
 Hvilken medicin behandler bedst depression hos voksne? [Internet]. Sst.dk. 2021 [cited 20 October 2021]. Available from: https://www.sst.dk/da/nyheder/2019/hvilken-medicin-behandler-bedst-depression-hos-voksne
 En moderne, åben og inkluderende indsats for mennesker med psykiske lidelser [Internet]. Copenhagen: Ministeriet for Sundhed og Forebyggelse; 2013 p. 50. Available from: https://im.dk/publikationer/2013/okt/en-moderne-aaben-og-inkluderende-indsats-for-mennesker-med-psykiske-lidelser
 Depression - Fakta og forebyggelse [Internet]. København: Sundhedsstyrelsen; 2005. Available from: https://www.sst.dk/da/udgivelser/2005/depression---fakta-og-forebyggelse
 Number of people with depression [Internet]. Our World in Data. 2021 [cited 20 October 2021]. Available from: https://ourworldindata.org/grapher/number-of-people-with-depression?country=~OWID_WRL
 Global and regional population estimates (US Census Bureau vs. UN) [Internet]. Our World in Data. 2021 [cited 20 October 2021]. Available from: https://ourworldindata.org/grapher/global-and-regional-population-estimates-us-census-bureau-vs-un?country=~OWID_WRL
 Guldin M. Næste bølge i coronakrisen: de psykiske reaktioner - Alt om psykologi [Internet]. Alt om psykologi. 2021 [cited 20 October 2021]. Available from: https://altompsykologi.dk/2021/03/naeste-boelge-i-coronakrisen-de-psykiske-reaktioner/
 Sønderskov K, Dinesen P, Santini Z, Østergaard S. The depressive state of Denmark during the COVID-19 pandemic. Acta Neuropsychiatrica. 2020;32(4):226-228.
 Javed B, Sarwer A, Soto E, Mashwani Z. The coronavirus ( COVID ‐19) pandemic's impact on mental health. The International Journal of Health Planning and Management [Internet]. 2020;35(5):993-996. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7361582/
 Panchal N, Kamal R, Cox C, Garfield R. The Implications of COVID-19 for Mental Health and Substance Use [Internet]. KFF. 2021 [cited 20 October 2021]. Available from: https://www.kff.org/coronavirus-covid-19/issue-brief/the-implications-of-covid-19-for-mental-health-and-substance-use/
 Wong L, Alias H, Md Fuzi A, Omar I, Mohamad Nor A, Tan M et al. Escalating progression of mental health disorders during the COVID-19 pandemic: Evidence from a nationwide survey. PLOS ONE [Internet]. 2021;16(3):e0248916. Available from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0248916
 Martin M. On the Evolution of Depression. Philosophy, Psychiatry, & Psychology. 2002;9(3):255-259.
 Hari J. Lost connections. London: Bloomsbury; 2018.
 Paykel E. Basic concepts of depression. Dialogues in Clinical Neuroscience. 2008;10(3):279-289.
 ICD-11 - ICD-11 for Mortality and Morbidity Statistics [Internet]. Icd.who.int. 2021 [cited 20 October 2021]. Available from: https://icd.who.int/browse11/l-m/en#/http://id.who.int/icd/entity/1563440232
 Üstün T, Jacob R, Çelik C, Lewalle P, Kostanjsek N. Production of ICD-11: The overall revision process [Internet]. Who.int. 2021 [cited 20 October 2021]. Available from: https://www.who.int/classifications/icd/ICDRevision.pdf
 Gupta A. Definitions [Internet]. Plato.stanford.edu. 2021 [cited 20 October 2021]. Available from: https://plato.stanford.edu/entries/definitions/
 iff means if and only if
 ICD-11 - ICD-11 for Mortality and Morbidity Statistics [Internet]. Icd.who.int. 2021 [cited 20 October 2021]. Available from: https://icd.who.int/browse11/l-m/en#/http://id.who.int/icd/entity/578635574
 American Psychiatric Association. DSM-5. Fifth edition: 2013