Which of the following expresses an incidence rate measured for a subgroup of a population?
D. Mortality rates are a special type of incidence rates where ‘death’ is the defined ‘case’ of interest. Crude mortality rate is the ratio between number of deaths due to all cause in a population and total population size. Cause-specific mortality rate, for example alcohol-specific mortality, refers to the ratio between the number of deaths due to alcohol in a population and total population size. A standardized rate is a rate applicable to a hypothetical population with an adjusted variable, for example age. As population samples are heterogeneous, crude rates from one population may not be comparable to another population. For example suicide rates in inner London may not be comparable to rates in rural Yorkshire, as the working-age population may be higher in London, spuriously increasing suicide rates. Hence, standardized hypothetical populations are used on which observed rates from a population are applied and adjusted values are derived. These standardized values are easily comparable, but they are not subgroup incidence rates.
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Which of the following correctly expresses proportional mortality rate due to anorexia nervosa?
B. Proportionate mortality rate is a measure of the contribution of a disease to societal mortality burden. It is given by the ratio between deaths due to a specific cause and total number of deaths in a population. Case fatality rate is the ratio between the number of deaths due to a specific disease and number of persons affected by the disease in a population. It is a measure of the fatal severity of the disease studied. For example 15 patients out of 100 with anorexia will die due to its complications. Choice A refers to cause-specific mortality rate while choice D refers to case fatality rate.
Which of the following is a major advantage in using standardized morality rate compared to crude mortality rate?
A. The true value of the number of deaths in a population is obtained using crude mortality figures. Both standardized and crude rates are expressed in the same units of incidence. Standardized rates are not the same as specific rates. Disease-specific rates can give an idea about cause of death in a population. Standardized rates increase comparability, not the accuracy of measurement of mortality in a population.
There are 65 suicides in a population of 1300 patients with schizophrenia. The rate 65/1300 refers to which one of the following?
B. This is an example of cause-specific (suicide is the cause) mortality rate in a population (number of schizophrenia patients). If the comparison is between the number of patients died with a diagnosis of schizophrenia and total number of patients at a given time interval, then this becomes case fatality rate for schizophrenia. If deaths due to suicides in a population with schizophrenia are compared with all-cause deaths in the same population then this will be proportionate mortality due to suicide. A ‘case’ of suicide cannot be identified alive, though patients who attempted suicides can be identified. So describing a ‘case’ fatality rate for suicide is meaningless. Nevertheless, method-specific case fatality can be derived for various modes of suicide attempts.
Patients with undiagnosed subsyndromal hypomania have clinical characteristics closely resembling which one of the following diagnoses?
D. In large epidemiological studies, a consistent 1.5% prevalence is quoted for bipolar disorders. It is unclear whether there is an over-inclusion of depressive disorders and underdiagnosis of bipolar type 2 disorder in these surveys. Hypomania, being positively appraised by patients themselves, is often missed in structured, non-clinician interviews. Angst et al., in a 20-year-long prospective study, observed that patients with depression and clinically undiagnosed subsyndromal hypomania have similar risk factors, course, and outcome compared to bipolar disorder type 2.
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