Interpreting Data Regarding Correlations, Risk Factors, Prevention, and Therapy Flashcards by Taryn W

what is the correlation coefficient (r)

mathematical expression of strength and direction of correlation between variables

range from -1 to +1
+/-0.5 indicates a weak correlation

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interpret:

a study of the amount of smoking and the incidence of lung cancer generates a correlation coefficient of r=+0.7

indicates a strong positive correlation

ie: increased amounts of smoking are strongly associated with an increased incidence of lung cancer

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pearson product-moment correlation (r) is used for:

spearman rank-order correlation (rho) is used for:

continuous data

ordinal scale data

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how is correlation represented

scattergrams

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what is the correlation of determination

expresses the proportion of variance in a variable explained by another variable

r^2, expressed as a percentage

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interpret:

correlating exercise levels with serum glucose levels generates r=-0.4, squaring this value results in a coefficient of determination of 0.16 (16%)

indicates that 16% of the variance in serum glucose levels can be accounted for by the exercise level
this correlation is weak and doesnt necessarily mean that increased exercise causes a decrease in serum glucose

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what is regression analysis

linear regression

multiple regression

a mathematical technique used to predict the value of one variable based on another
–> only useful in highly correlated variables

linear: predicts one variable based on another
Multiple: predicts the value of a variable based on multiple covariates (ex rate of heart attack based on cholesterol, bp, weight, age) & adjusts data to eliminate effects of confounding vars

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what are the ways to measure effects of risk factors?

odds ratio (OR)
absolute risk (AR)
attributable risk 
relative risk (RR)

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what is the odds ratio

measures the degree of association of a risk factor with a disease or outcome

ratio of the odds that a case was exposed to the odds that a control was exposed
used when actual incidence of a disease is not measured, such as case-control

=odds that a case was exposed to risk factor/odds that control was exposed to risk factor

= (#obese diabetic/#nonobese diabetic)/(#non-diabetic obese/# non-diabetic non-obese)

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=odds that a case was exposed to risk factor/odds that control was exposed to risk factor

odds ratio (OR)

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what does odds ratio show

shows an association between risk factors and condition, but is a relatively weak indicator of causality

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what is the absolute risk (AR)?

the risk over a given time period of contracting a disease

synonymous with incidence
done for control group and for experimental group

=number developing disease/total number

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=number developing disease/total number

absolute risk (AR)

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what is attributable risk?

the difference in risk between exposed and unexposed groups
-the amount of disease ocurrances that are attributable to the exposure

=AR (exposed) - AR (unexposed)

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=AR (exposed) - AR (unexposed)

attributable risk

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what is relative risk?

measures how many times exposure to a risk factor increases the risk of contracting a disease
-ratio of the absolute risk of disease among those exposed to absolute risk among those not exposed to the risk factor

can only be calculated when incidence is measured (such as cohort study)
-> shows not only association but is a more powerful indicator of causality

=AR of disease among exposed/AR of disease among non-exposed

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=AR of disease among exposed/AR of disease among non-exposed

relative risk

the risk over a given time period of contracting a disease

synonymous with incidence
done for control group and for experimental group

absolute risk

the difference in risk between exposed and unexposed groups

-the amount of disease occurrences that are attributable to the exposure

attributable risk

Interpret:

a cohort study investigating obesity as a risk factor for diabetes determines a relative risk of 5

obese are 5X as likely to develop diabetes compared to non-diabetes

interpret

attributable risk of obesity to diabetes is 16%

16% of risk for diabetes comes from obesity

what are the ways to interpret data regarding prevention and therapy?

relative risk reduction
absolute risk reduction
number needed to treat
cost of intervention

what is relative risk reduction (RRR)

measures the decrease in relative risk due to an intervention

=1-relative risk

measures the decrease in relative risk due to an intervention is:

relative risk reduciton

=1- RR

relative risk reduction

interpret: obese patients are treated with an aggressive diet/exercise program. compared to controls the treated patients are found to have a RR of 0.25. the RRR is thus 1-0.25=0.75. what does this mean?

treatment reduced the relative risk by 75%

what is absolute risk reduction (ARR)

decrease in absolute risk (decrease in incidence) of an outcome due to an intervention =AR(Control) - AR (treatment)

=AR(Control) - AR (treatment)

ARR

decrease in absolute risk (decrease in incidence) of an outcome due to an intervention is:

ARR

interpret: obese patients are treated with an aggressive diet/exercise program. controls are found to have an AR of diabetes of 0.4. The study group AR of diabetes is 0.1. The ARR is 0.4-0.1=0.3. what does this mean

the treatment reduced the absolute risk by 30%

what is the difference between ARR and attributable risk? (they are calculated the same way..)

- AR is generally used when assessing impact of risk factors | - ARR is generally used when accessing the impact of prevention/treatment

What is the difference between RRR and ARR?

- RRR is how many times exposure to a risk factor increases risk of contracting disease - -> higher, more impressive number than ARR - ARR is the decrease in absolute risk of an outcome due to an intervention - -> smaller, less impressive than RRR but ARR is more clinically relavant

why is ARR more clinically relevant than RRR

it incorporates the incidence of the disease/outcome being prevented

what is the number needed to treat (NNT)

calculation of the number of patients who would be required to receive treatment in order to prevent one negative outcome =1/ARR

=1/ARR

NNT

calculation of the number of patients who would be required to receive treatment in order to prevent one negative outcome

NNT

interpret: ARR for obese patients receiving aggressive diet and exercise was found to be 0.3. Calculate NNT. what does this mean?

NNT= 1/0.3 = 3.3 | this means that 3.3 patients would need to receive treatment in order to prevent one case of diabetes

what is the cost of intervention

a calculation of the cost of preventing one negative outcome =NNTx cost of 1 intervention

what is quality of life years (QALY)

measure of length of life weighed by a valuation of health related to quality of life - quality of life modifier is calculated based on questions regarding ability to walk, self care, ability to perform usual activities, pain, anxiety, depression. - generally this number ranges from 0-1, 1 is perfect health