Exam 3 Study Guide BBH 440 PDF

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Study Guide for Exam 3 BBH/HPA 440 1) Morbidity rates a) Morbidity: the state of being diseased or unhealthy in a population. Measures include: ratio, proportions, rates. b) Ratios, proportions, & rates i) Ratios: comparison of two numbers (x and y) (1) Can be expressed as X:Y, X/Y, X to Y. The values of X and Y are independent such that the values of X are not contained in Y. (2) Example: in 2008, there were 36,030 suicides in the U.S., of which 28,447 were male and 7,583 were female. Ratio of males to females who committed suicide is 3.75:1 ii) Proportions: the values of X are contained in Y, typically expressed as a percentage (1) Example: proportion of suicide cases who were male: 79% iii) Rates: a frequency measure often used in epidemiological studies. It is a proportion with some reference to time. (1) Example: if 617 males were observed for 1 year and 81 developed IBS, the proportion of men who developed IBD would be 81/617 or 13.1%. The rate of new cases in IBD (incidence rate) would be 81 per 617 people per year c) Incidence rate: the number of new cases of a disease/health-related condition during a time period divided by the population at risk of having the disease or condition during that time period i) Uses of incidence rates (1) reflect the operation of causal factors (2) if incidence is increasing, there is suspicion that the causal factors and risks are increasing (3) if incidence is decreasing, it provides evidence of primary prevention (4) incidence rates for groups that differ on some attribute or "exposure" are frequently compared to identify risk and causal factors (5) frequently used to compare incidence in the "exposed" group to the incidence in the "nonexposed" group ii) Prevalence = Incidence x Duration iii) Attack rate (1) an incident rate but is usually used in special situations involving illnesses of short duration (e.g., food poisoning, chemical exposure) (2) where the risk is for a limited group of people (3) attack rates help isolate the source of exposure iv) Secondary attack rate (1) used in infectious disease situations when a limited time period exists, and there is a short incubation period (2) limited time period (3) short incubation period v) Incidence-density rate (1) denominator is sum of time each person was observed rather than the number of individuals (2) used when people are at risk for different periods of time (e.g., rate of injuries at a factory with full- and part-time workers) d) Prevalence rates: the total number of cases or instances of a disease or health-related condition divided by the population at risk of having the disease or condition some unit of time i) Point prevalence: the total number of cases or instances of death/health-related condition at a single point in time divided by the population at risk of having the disease or condition at that particular point in time (1) (total # of cases at a single point in time)/(population at risk at single point in time) x 10n ii) Period prevalence: the total number of cases or instances of disease/health-related condition during a specific period of time divided by the population at risk of having the disease or condition during that period

Study Guide for Exam 3 BBH/HPA 440 (1) (total # of cases during period of time)/ (population at risk during period [average period]) x 10n iii) Uses of prevalence rates (1) Affected by several factors, reflects the burden of the disease on society (2) Can be used to estimate the need for health care services, prevention activities, etc. for different groups or locations (3) Can be used to allocate funding and resources (4) Can sometimes be used to estimate the risk of being diseased at a specific time or period iv) Ways prevalence rates may be increased or decreased (1) Increased by: (a) Immigration of cases (new cases moving in) (b) Emigration of healthy (healthy moving out) (c) Immigration of susceptible cases or those with potential for becoming cases (e.g., the aged) (d) Prolongation of life of cases without cure (increase in duration of disease) (e) Increase in occurrence of new cases (increased incidence) (2) Decreased by: (a) Immigration of healthy (b) Emigration of cases (c) Improved cure rates (d) Increased death rates (e) Shorter duration of disease (f) Decreased incidence v) Influence of surveillance on prevalence (1) Prevalence affected by the quality of the surveillance system (2) Rates for emerging chronic disease sometimes increase as more attention is given to it in the press, scientific literature, and by clinicians 2) Mortality a) Mortality: the epidemiological and vital statistic term for death b) Death certificate: cause of death (immediate and underlying) i) Information included (e.g. immediate, underlying causes of death) (1) Immediate cause of death (2) Underlying causes of death (3) Manner of death & autopsy ii) Problems with inaccuracies in data: immediate vs. underlying causes ( sequence), validity of diagnosis and other information c) Epidemiological transition: term used by demographers and epidemiologists due to innovating treatments and control over common diseases i) Characterized by: (1) Decline in deaths from infectious diseases (2) Increase in deaths from degenerative diseases (3) Decline in overall death rates (4) Increased life expectancy (5) Elimination of mortality spikes corresponding to epidemics d) Mortality rates (for all rates know definition, advantages, & disadvantages) i) Crude mortality rate: total number of deaths divided by the estimation of the total population, number of deaths within a period of time/population at risk, varies from group to group (1) Advantages: easy to calculate, useful summary rate (2) Disadvantages: will vary from group to group if populations differ in sex, race, etc.

Study Guide for Exam 3 BBH/HPA 440 Formula:

ii) Adjusted mortality rate: a summary mortality rate to balance out the influence of some demographic characteristic, only an estimate and much more difficult to compute (1) Why do we adjust rates? (a) Epidemiological comparisons (b) To refine causality between risk and outcome (c) To disentangle effects of confounders (2) Advantages: good summary rate, easily comparable across populations (3) Disadvantages: only an estimate, magnitude will depend on standard population, more difficult to compute (4) Direct method (a) Know all steps to direct method and why they are done (i) If rate increases after adjustment, study population is younger than the standard (ii) If rate decreases after adjustment, study population is older than standard (b) Know reasons for increases and decreases in mortality rate after adjustment (i) Use a standard population (subgroups must be represented) (ii) Apply age specific rates in each study population to the reference population (iii) Get expected number of cases if the study population was the same as the standard population (iv) Sum the cases and divide by total size of standard population to get age adjusted rate (5) Indirect method (a) Used when age-specific mortality rates are missing or difficult to calculate, if you don’t know the age-specific rates or the data is unreliable (b) Know steps to indirect method and why they are done (i) Select reference population (also need to be able to get age-specific rate) (ii) Apply age-specific rates from reference population to study population (iii) Add up cases and divide the # of observed deaths by the # of expected deaths for standardized mortality ratio (c) Know interpretation of SMR after adjustment (i) SMR, standardized mortality ratio = observed/expected (ii) If SMR = 1, health events in population are as expected (iii) If SMR > 1, health events in population are greater than expected (iv) If SMR 1 ii) % decrease change = (1 – RR) x 100 if RR < 1 iii) Can be used to interpret relative risk or odds ratio iv) Know formula & be able to calculate for both increased and decreased risks Make sure you can look at a table (like those in the examples and from the literature) and answer questions about the OR or RR statistics you see there! Attributable risk i) Definition: the proportion of disease among the exposed that actually results from the exposure. Represents the proportion of the disease that could be eliminated if the exposure could be eliminated. Estimated in different ways, used to estimate impact on the population ii) Formula for attributable risk difference (1) The difference between the exposed and unexposed incidence rates. Also known as: excess rate, rate of difference (2) Attributable risk difference: Ie - Iu iii) How to interpret iv) Population attributable risk proportion (1) Know what measures are needed for formula, how changes in variables affect the outcome, and how to interpret (a) The proportion of the disease in the whole population that could be eliminated if the exposure was eliminated (b) The population attributable risk proportion takes into consideration the prevalence of the exposure (c) PARP = Pe (RR – 1) / [1 + Pe (RR – 1)], where RR – relative risk, Pe – proportion of the population that is exposed (2) Know that prevalence affects PARP...