morbidity
/ mor-BID-ity /
Everyone knows that people eventually die — that is mortality. But long before that, people get sick, get hurt, become disabled, or need care. A worker breaks an ankle and cannot earn for three months; an older person can no longer dress or bathe alone; someone is diagnosed with cancer and faces huge bills. Morbidity is the umbrella word for all of this: the occurrence and the course of illness, injury, and disability in a population.
Where a life actuary asks 'what is the chance this person dies this year?', a health actuary asks 'what is the chance this person becomes sick or disabled this year, and if they do, how long does it last and how much does it cost?'. So morbidity is richer than mortality: it has both a chance of onset (incidence) and a duration or recovery pattern (how long someone stays disabled, how long a hospital stay runs). For example, the morbidity assumption for a disability policy might say 'about 4 in 1,000 healthy workers aged 45 become disabled in a year, and the typical claim then lasts a couple of years before recovery, retirement, or death'.
Morbidity is the central raw material of health, disability, and long-term-care insurance, and it is harder to pin down than mortality. Death is unambiguous and recorded everywhere; 'being sick' or 'being disabled' depends on definitions, on how generous a benefit is, on the economy (people claim more in a recession), and on medical practice that changes year to year. That is why morbidity tables and assumptions are revisited far more often, and treated more cautiously, than mortality tables.
An insurer pricing group disability uses a morbidity assumption with two parts: an incidence rate (say 0.5% of insured workers go on claim each year) and a continuance pattern (of those, half are still claiming after one year, a quarter after two). Both parts together drive the cost — not just how often people get hurt, but how long they stay hurt.
Morbidity = how often people fall ill or disabled, AND how long it lasts.
Do not confuse morbidity with mortality: a disease can have low mortality (rarely fatal) but high morbidity (very common and disabling), like arthritis. Health insurance cares about both, but morbidity is its main driver.