Lecture 24-32 - Intro To Biostats In Epidemiology Flashcards Preview

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Flashcards in Lecture 24-32 - Intro To Biostats In Epidemiology Deck (38)
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1

What are the 3 primary levels of variable?

L24 S5

-nominal
-ordinal
-interval/ratio

2

What are the 3 key attributes of variables?

L24 S5

-order/magnitude
-consistency of scale
-rational absolute zero

3

What is nominal data?
What are its characteristics?

L24 S6

-consists of labeled variables without quantitative characteristics
-can be dichotomous or binary in nature

-no order/magnitude
-no consistency of scale

4

What is ordinal data?
What are its attributes?

-contains rank-able categories that are not evenly spaced

-yes order/magnitude
-no consistency of scale

5

What is interval data?
What are its attributes?

L24 S8

-rankable categories that are evenly spaced
-arbitrary 0 value that does not mean absence of measured value

-yes order/magnitude
-yes consistency of scale
-no rational absolute zero

6

What is ratio data?
What are its attributes?

L24 S8

-rankable categories that are evenly spaced
-absolute 0 value that indicates absence of measured value

-yes order/magnitude
-yes consistency of scale
-yes rational absolute zero

7

What is the order of specificity of data types?
In which direction(s) can you convert data types?

L25 S12

Nominal < Ordinal < Interval < Ratio

Data can only be converted down in specificity, not up

8

What percentage of data is within one, two, and three standard deviations of the mean in a normally distributed data set?

L26 S23

One deviation (-1 to +1):
-68%

Two deviations (-2 to +2):
-95%

Three deviations (-3 to +3):
-99.7%

9

What is name given to the types of tests that are used on normally distributed data sets?

L26 S23

-parametric test

-or-

-interval test

10

What determines if a data set is skewed?
What makes a data set positively skewed?
Negatively skewed?

L26 S24-25

-mean and median differ from one another

Positively skewed:
-mean is higher than median
-tail goes to the right/positive direction

Negatively skewed:
-mean is lower than median
-tail goes to the left/negative direction

11

What does skewness represent?

L26 S35

-the measure of asymmetry of a distribution

12

What is kurtosis?
What do a negative, zero, and positive kurtosis represent?

L26 S37

-measure of the extent to which data clusters around the mean

Negative kurtosis:
-less cluster

Zero kurtosis:
-normal distribution

Positive kurtosis:
-more cluster

13

Calculating the mean on nominal and ordinal data can be done but it can’t be interpreted, why is this?

L26 S40-43

The numbers assigned to data is arbitrary and can be changed. (There is no consistency of scale and there are no units)

14

What is the name of the test that can be used to assess for equalness of variance between groups?

L26 S44

-Levene’s test

15

How do you assess data sets that are not evenly distributed?

L26 S45

-use tests that do not require normal distribution (non-parametric tests)
-transform the data to a standard value (z-score or log transformation) to make it normally distributed

16

What are type 1 and type 2 errors?

L26 S47-49

Type 1 error:
-when the null hypothesis is true and should have been accepted, but wasn’t
-there is no true difference between groups but it was said that there is

Type 2 error:
-when the null hypothesis is false and should have been rejected but wasn’t
-there is a true difference between groups but it was said that their isn’t

17

What factors should be looked at to determine if a study’s results are statistically significant?

L27 S50

-power: the ability of a test to detect if there are true differences between groups
-sample size: the greater the sample size the greater the studies ability to detect if there is a difference between groups
-p value
-confidence interval

19

What are the typical accepted type 1 and type 2 error rates?

L27 S51

Type 1:
-5%

Type 2:
-20%

20

What are some ways that p value can be interpreted as?

L27 S56

-probability of making a type 1 error if the null hypothesis is rejected
-probability of erroneously claiming a difference between groups when one does not really exist
-probability of obtaining group differences as great or greater if the groups were actually the same or equal
-probability of obtaining test statistic as high/higher if the groups were actually the same/equal

21

Where is it desired to see that there is no statistical difference between groups?

L27

-baseline data

-Levene’s test

22

What does power mean with respects to statistical significance?

L27 S50

-the ability of a study to determine if there is a true difference between groups

1 - (type 2 error rate)

23

What is a confidence interval?

L28 S63

-percentage of confidence that statistically includes the real relationship being compared

24

If the confidence interval of a ratio contains the number ____________ it is statistically insignificant.

If the confidence interval of an absolute difference contains the number __________ it is statistically insignificant.

L28 S65-66

1; 0

25

What factors should be included in the interpretation of a confidence interval?

L29 S65

-level of confidence
-interpretation of range
-statement of statistical significance
-statement of the groups being compared

26

What questions should be asked when selecting a statistical test?

L29 S91

-what is the level of data being collected (nominal/ordinal/interval)?
-what type of comparison/assessment is desired (frequencies/counts/proportion)
-how many groups are being compared (2 or >3) ?
-is the data independent or related (from the same person or not)?

27

What is a correlation test?

What are the correlation tests for each data level?

L29 S75

-provides a quantitative measure of the strength and direction of relationship between variable

Nominal:
-contingency coefficient

Ordinal:
-Spearman correlation

Interval:
-Pearson correlation

28

What is a survival test?

What are the survival tests for each level of data?

L30 S81-83

-compares proportion of event occurrence over time between groups
-“changes over time”
-“time to event”
-can be graphed as a Kaplan-Meier curve (regardless of data level)

Nominal:
-Log-Rank test

Ordinal:
-Cox-Proportional Hazards test

Interval:
-Kaplan-Meier test

29

What is a regression test?

What are the regression tests for each level of data?

L30 S84-86

-measure of relationship between variables to predict an outcome
-able to calculate an odds ratio
-“predict”

Nominal:
-logistic regression

Ordinal:
-multinomial logistic regression

Interval:
-linear regression

30

What test is used to evaluate NOMINAL data of 2 INDEPENDENT groups and >3 INDEPENDENT groups?

L31 S93

2 groups:
-Pearson’s Chi-square test

>3 groups:
-chi-square test of independence


When there are less than 5 observations of an occurrence, Fisher’s exact test is used instead of the two listed above.

31

What must be done in groups of NOMINAL data of more than 3 when there is found to be a statistically significant difference between groups?

L31 S95

Post-hoc testing must be done to determine between which groups the statistically significant difference occurs.

ex. Bonferroni test of inequality (Bonferroni correction)