question

mortality rate

answer

Total no of deaths from all causes in year/No of persons in the population at midyear *time must be specified*

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cause specific mortality rate

answer

- limiting the rate of death to a certain disease - No of deaths from lung cancer in one year/ No of persons in the population at midyear

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case-fatality rate

answer

- % of people who have a certain disease die within a certain time after diagnosis - measure severity of the disease - No of individuals dying during a specified period of time after disease onset or diagnosis/No. of individuals with the specified disease

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morbidity

answer

usually refers to the incidence of disease in the population

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absolute risk

answer

- incidence of a disease in a population - indicate the magnitude of the risk in a group of people with a certain exposure, but because it does not take into consideration the risk of disease in nonexposed individuals

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relative risk formula

answer

(risk in exposed)/(risk in nonexposed)

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relative risk

answer

probability of developing a disease in exposed people compared to the probability of developing a disease in nonexposed people, - ratio of the two probabilities. - used in COHORT studies

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how to interpret relative risk

answer

- RR= 1: no association - RR>1: positive association, possibly causal -RR<1: negative association, possibly protective

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odds ratio for cohort studies

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- (odds that an exposed person develops disease) / (odds that a non-exposed person develops disease) - (a/b)/(c/d) = (ad/bc)

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odds ratio for case control studies

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- (odds that a case was exposed)/(odds that a control was exposed) - ad/bc

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attributable risk

answer

amount/proportion of disease incidence (or disease risk) that can be attributed to a specific exposure.

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attributable risk formula

answer

(incidence in exposed group) - (incidence in nonexposed group)/ (incidence of people exposed)

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population attributable risk

answer

- proportion of the disease incidence in a total population (including both exposed and nonexposed people) that can be attributed to a specific exposure

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pop attributable risk formula

answer

- (incidence in total pop) - (incidence in nonexposed group (background risk)) / (incidence in total pop) - attributable risk x prevalence of exposure in the population

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absolute risk reduction

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- tells how much better or worse one treatment is at reducing a particular outcome in terms of the actual numbers (or rates) of people who experience the outcome compared with another treatment. - simple difference between rates

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relative risk reduction

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- difference between the likelihood of an event happening in two groups, expressed as a percentage of the risk for one of the groups. - ratio of the risks or proportional difference

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number needed to treat

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- expresses the results of RCT - number of patients who would need to be treated (NNT) to prevent one adverse outcome/ death.

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number needed to treat formula

answer

(1)/ ((rate in untreated group) - (rate in treated group))

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median survival time

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length of time that half of the study population survives.

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kaplan meier

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identify the exact point in time when each death occurred so that each death terminates the previous interval and a new interval (and a new row in the Kaplan-Meier table) is started. - number of persons who died at that point/number alive up to that point

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intention to treat analysis

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- includes all randomized patients in the groups to which they were randomly assigned, regardless of their adherence with the entry criteria, regardless of the treatment they actually received, and regardless of subsequent withdrawal from treatment or deviation from the protocol - "once randomized, always randomized"

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confounding

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- a factor that alters the observed association between exposure and outcome bc it is related to both the exposure and the outcome - cannot be in the causal pathway

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how to account for confounding

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- randomization - restriction - matching in case-control - stratification - multivariate analyses

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how to check for confounding

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- stratify tables based on the potential confounding variable and examine across the RRs or OR to see if they are different - use an adjustment technique and compare adjusted estimate to the crude results

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interaction

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- when the effect of exposure on outcome of interest depends upon the level of a third variable - the presence of a second factor changes the effect of a risk factor on disease occurrence

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how to check for interaction

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- stratify data on the potentially interactive factor - compared the measures of association - significant differences imply that interaction is present

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positive interaction

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- the incidence rate is greater than expected - aka synergy

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negative interaction

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- the incidence rate is less than expected - aka antagonism

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selection bias

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- systematic error in which cases and controls, or exposed and non- exposed individuals, were selected is such that an apparent association is observed—even if, in reality, exposure and disease are not associated - happens bc of nonresponse of potential study subjects. - should characterize nonresponders

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information bias

answer

- means for obtaining information about the subjects in the study are inadequate. - some info gathered regarding exposures and/or disease outcomes is incorrect.

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types of information bias

answer

- Bias in abstracting records - Bias in interviewing - Bias from surrogate interviews - Surveillance bias - Recall bias Reporting bias

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differential misclassification

answer

- rate of misclassification differs in different study groups - misclassification of exposure may occur such that unexposed cases are misclassified as being exposed more often than the unexposed controls are misclassified as being exposed. - can occur due to recall bias - could cause a falsely high odds ratio

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non-differential misclassification

answer

- results from the degree of inaccuracy that charac- terizes how information is obtained from any study group—either cases and controls or exposed and nonexposed persons - problem inherent in the data collection methods - RR/OR tends to be diluted and is shifted towards 1 (less likely to detect an association) - leads to bias towards the null

question

necessary and sufficient

answer

Without that factor, the disease never develops (the factor is necessary), and in the presence of that factor, the disease always develops (the factor is sufficient)

question

necessary and insufficient

answer

- each factor is necessary, but not, in itself, sufficient to cause the disease - multiple factors are required, often in a specific temporal sequence

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unnecessary and sufficient

answer

factor alone can produce the disease, but so can other factors that are acting alone

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unnecessary and insufficient

answer

factor, by itself, is neither sufficient nor necessary to produce disease

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screening

answer

- To detect potential disease indicators - done on large numbers of asymptomatic, but potentially at risk individuals

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diagnostic test

answer

- To establish presence/absence of disease - Symptomatic individuals to establish diagnosis, or asymptomatic individuals with a positive screening test

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conditions for effective screening

answer

- when treatment before symptoms occur is more effective than treatment that is delayed until symptoms appear. - accurately and efficiently identifies people with pre-clinical disease

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lead time bias

answer

- screening test advances the time of diagnosis, but no true prolongation of life occurs - give appearance of longer survival for the persons screen vs those not - if there is no treatment for the ones screened earlier, then the survival time is the same for both

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length bias

answer

- Overestimation of survival duration among screening-detected cases caused by the relative excess of slowly progressing cases. - These cases are disproportionately identified by screening because the probability of detection is directly proportional to the length of time during which they are detectable

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volunteer bias

answer

people who participate in health programs or studies differ in many ways from those who do not: in their health status, attitudes, educational and socioeconomic levels, and other factors.

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sensitivity

answer

- proportion of individuals with the disease who have a positive test - (A)/(A+C)

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specificity

answer

- proportion of individuals without disease who have a negative test - (D)/(B+D)

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positive predictive value

answer

- proportion of all patients who test positive who actually have the disease - (true positive)/(true positives + false positives) - increasing prevalence increases PPV

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negative predictive value

answer

- proportion of all patients who test negative who actually do not have the disease - (true negatives)/ (true negatives + false negatives) - increasing prevalence decreases NPV

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kappa

answer

measures inter-rater agreement for qualitative (categorical) items

question

1- sensitivity

answer

- probability of a negative test if there is disease - false negative rate

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1 - specificity

answer

- probability of a positive test if there is no disease - false positive rate

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precision

answer

increasing sample size increases precision

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