Intro to Biostatistics

Question 1

what are the two types of discrete/categorical variables?

Answer 1

nominal and ordinal

Question 2

what is a nominal variable

Answer 2

discrete group

ex: male/female, smoker/non-smoker

Question 3

what is an ordinal variable

Answer 3

ordered without meaningful intervals

ex: class rank

Question 4

what are the two types of continuous variables?

Answer 4

interval and ratio

–> can take continuous data and turn it into categorical data

Question 5

what is an interval variable

Answer 5

ordered with meaningful intervals, without an absolute zero - rarely used in medical research

ex: temperature in celsius

Question 6

what is a ratio variable?

Answer 6

interval data with an absolute zero

ex: age, weight, cholesterol levels

Question 7

define frequency distribution

Answer 7

a systematic arrangement of numerical data from the lowest to highest

Question 8

what is a systematic arrangement of numerical data from the lowest to highest

Answer 8

frequency distribution

Question 9

what are the three ways grouped data can be presented?

Answer 9

frequency - absolute number in each category

relative frequency - percent in each category

cumulative frequency - cumulative percent

Question 10

what is a bar graph

Answer 10

grouped frequencies used to display nominal data

-ex: cholesterol by gender

Question 11

how would you graph cholesterol by gender?

Answer 11

bar graph

Question 12

how would you graph grouped frequencies used to display nominal data?

Answer 12

bar graph

Question 13

what is a histogram

Answer 13

grouped frequencies generally used to display continuous variables

Question 14

what is a frequency polygon

Answer 14

midpoints of each group joined by straight line used to display continuous variables

“line graph”

–> excellent for displaying distribution of sample

Question 15

what type of graph would you used to show the distribution of a sample

Answer 15

frequency polygon

Question 16

what is a cumulative frequency polygon

Answer 16

displays the cumulative frequency for continuous variables

“100% of sample has cholesterol level below 260… 15% of sample has cholesterol level below 190”

Question 17

what type of graph would you use to approximate percentiles?

Answer 17

cumulative frequency polygon

Question 18

what is a survival curve

Answer 18

plots death or endpoints

- Kaplan Meier method preferred

Question 19

why are simple survival curves not useful in actual studies?

what is the solution to these problems

Answer 19

• patients are not enrolled at the same time
• patients drop out
• patients are followed for varying lengths of time

-Kaplan Meier method

Question 20

what is the kaplan meier method and why does it solve the problem created by simple survival curves

Answer 20

• used to plot survival in medical research
• adjusts data to reflect the patients who are not followed for the entire study
• also referred to as censored survival data

Question 21

what is a normal/gaussian distribution

Answer 21

frequency polygon with the appearance of a symmetrical bell-shaped curve; often generated by biologic/medical data

• many statistical manipulations and inferences are dependent on the assumption of this distribution
• more accurately approximated as sample size increases

Question 22

positive and negative skewing refers to what part of the distribution.. the mean or the tail?

Answer 22

the tail

Question 23

what is mean

Answer 23

the average value

• sensitive to extreme scores
• can misrepresent a population dramatically

Question 24

what is median

Answer 24

middle value

Question 25

what is mode

Answer 25

the value that occurs the most frequently

Question 26

what is range

Answer 26

difference between the highest and lowest value

Question 27

what is variance

Answer 27

quantifies the scatter present in the distribution of values

• average of the squared differences from the mean
• not a very intuitive measurement, won’t be asked to calculate

Question 28

what is standard deviation (SD)

Answer 28

square root of the variance, much more intuitive

• most commonly used measure of variability
• the more spread out the sample distribution, the larger this SD

Question 29

what is the most commonly used measure of variability

Answer 29

standard deviation

Question 30

what percentage of the population falls within 1 standard deviation of the mean?

Answer 30

68%

Question 31

what percentage of the population falls within 2 standard deviations of the mean?

Answer 31

95%

Question 32

what percentage of the population falls within 3 standard deviations of the mean

Answer 32

99.7%

Question 33

What are z scores?

Answer 33

• used to transpose standard deviations into percentile data
• identical to the standard deviations they represent

-used when considering the percent of a population above or below a specific level

Question 34

what is the multiplication rule?

Answer 34

used to calculate the probability of 2 (or more) independent events both occurring

-p(a)xp(b) = p(a+b)

Question 35

how do you calculate the probability of 2 or more independent events both occurring?

Answer 35

multiplication rule

Question 36

what is the addition rule?

Answer 36

used to calculate the probability of either of 2 or more independent events occurring

-p(a or b) = P(a) + p(b) - P(a + b)

–> if mutually exclusive, P(a + b)=0

Question 37

how do you calculate the probability of either of 2 or more independent events occurring?

Answer 37

addition rule