Lecture 1 - Mean, Mode, etc.

Question 1

What is continuous data?

Answer 1

Data that can be divided up an infinite number of times. e.g. age decades -> years -> months -> days, etc.

Question 2

What is discrete data?

Answer 2

Data that cannot be divided up. aka integer data. e.g. # of fractures someone in a car accident has

Question 3

What is nominal data?

Answer 3

Data given arbitrary numeric labels. Used merely for identification. e.g. race. white = 0, black = 1, etc.

Question 4

What is ordinal data?

Answer 4

Ordered rankings with numeric labels. Numbers have meaning in relation to one another, but no intrinsic value. e.g. APGAR score.

Question 5

What is categorical data?

Answer 5

A type of ordinal data where higher numbers are in fact better, but the actual difference between is not known. e.g. pain scores.

Question 6

How is mean denoted in equations?

Answer 6

” X bar” (an X with a line on top of it)

Question 7

What is a major weakness of the mean?

Answer 7

It is strongly influenced by outlying values

Question 8

What are strengths of the median?

Answer 8

Impervious to outlying values

Question 9

What is a disadvantage of the median?

Answer 9

It only uses a small portion of the data set and does not give you an idea of the full range of values

Question 10

What is variance?

Answer 10

A measure of variability around the mean

Question 11

When should you use the mean vs. mode?

Answer 11

Generally use the mean when variance is low and the mode when variance is high. If the values are well spread out, report both.

Question 12

What is the standard deviation, numerically?

Answer 12

The square root of variance (converts variance back to a meaningful number for our actual data)

Question 13

What is large s?

Answer 13

Large spread. No hard and fast rule. Generally when SD is 50% (or more) as big as the mean.

Question 14

What is a small s?

Answer 14

Anything <25% = small

Question 15

What is the coefficient of variation (CV)?

Answer 15

Used to describe SD in relation the mean as a percentage. CV = (SD/mean) x100

Question 16

What direction is this data skewed?

Answer 16

Right, because the outlier is on the right.

Question 17

What are the significant values portrayed in this box plot?

Answer 17

Bottom of box = 25th percentile

Middle of box = 50th percentile

Top of box = 75th percentile

Whiskers typically 1.5 IQR or min/max

Question 18

What is sample probabilities?

Answer 18

Using sets of data and calculate probabilities on them that we hope are unbiased and can be extrapolated to a larger population of interest.

Question 19

What is the probability that any 2 events will occur?

Answer 19

P (event 1 OR event 2) =

P (event 1) + P (event 2) - P (both events occur)

If both events CANNOT occur (e.g. both being male and female), do not subtract P

Question 20

What does this phrase mean:
P (reduced FEV1| elevated IL-8) = 11/22 = 0.50?

Answer 20

What is the probability of reduced FEV1 GIVEN the people who have elevated IL-8 (usually limits the total sample size to a subset of the population) Also can be phrased “conditioned on”

Question 21

When are two probabilities independent?

Answer 21

When the probability of something happening alone is the same as under a certain condition. e.g. probability of seeing a blue car after having seen a red car is just the probablity of seeing a blue car.

Question 22

If two probabilities are independent, what is the probability of getting one twice in a row?

Answer 22

Multiply each probability.

P (event1 AND event2)=P (event1) x P (event2)

oFor a simple example, the probability of getting two heads in two tosses of a fair coin is just P (heads) x P (heads) = 0.50 x 0.50 = 0.25