Prelim #1

Question 1

Random Sample

Answer 1

each member of the population has an equal and independent chance of being selected

Question 2

Volunteer bias

Answer 2

volunteers for a study are likely to be different, on average, from the population

Question 3

sample of convenience

Answer 3

a collection of individuals that happen to be available at the time

Question 4

accuracy

Answer 4

an estimate is accurate (unbiased) if the average of estimates is centered on the true population value

Question 5

precision

Answer 5

a measure of how far apart repeated estimates might be, directly related to sample size

Question 6

experimental study

Answer 6

researcher randomly assigns individuals to treatment groups

Question 7

observational

Answer 7

assignment of treatments is not made by researcher

Question 8

categorical variables

Answer 8

describe membership in category/group. could be dichotomous (binary), ordinal (categories are ordered), or nominal (categories have no natural ordering)

Question 9

numerical/quantitative variables

Answer 9

quantitative measurements that have magnitude on a numerical scale. either continuous (can be measured) or discrete (can be counted, individual units)

Question 10

graphing: 1 categorical variable

Answer 10

frequency table, bar graph/bar plot

Question 11

graphing 1 numerical variable

Answer 11

histogram

Question 12

graphing 2 categorical variables

Answer 12

grouped bar graph, mosaic plot

Question 13

graphing 2 numerical variables

Answer 13

scatterplot, line graph (time)

Question 14

graphing 2 variables: one categorical and one numerical

Answer 14

strip chart, side-by-side box plot, multiple histograms

Question 15

mean vs median

Answer 15

mean is the center of gravity, median is middle measurement… mean is more affected by outliers/extreme values than median

Question 16

sample range

Answer 16

max-min…poor measure of distribution width…biased estimator of true range of the population

Question 17

sample variance (s^2)

Answer 17

the average squared difference from the mean….(standard deviation)^2

Question 18

standard (s)

Answer 18

positive square root of variance…it is related to the average distance between the mean and each observation…measure of the variability (or spread) of a distribution

Question 19

what percent of data falls within 1 sd of mean (normal distribution)?

Answer 19

2/3 (66%)

Question 20

what percent of data falls within 2 sd of mean (normal distribution)?

Answer 20

95%

Question 21

interquartile range

Answer 21

3rd quartile-1st quartile

Question 22

skew

Answer 22

measure of asymmetry…refers to pointy tail of a distribution

Question 23

box plot…where do whiskers extend to?

Answer 23

largest and smallest non-extreme observation

Question 24

standard error

Answer 24

the standard error of an estimator is the standard deviation of the estimator’s sampling distribution…measures precision

Question 25

standard error formula

Answer 25

se=s/square root (n)

Question 26

formula for rough confidence interval and assumptions

Answer 26

sample mean +/ 2SE

normally distributed population and sufficiently large sample size, random sample

Question 27

does confidence interval contain sample mean or true population mean?

Answer 27

true population mean

Question 28

standard errors (increase/decrease) with increasing sample size?

Answer 28

decrease (large samples yield more precise estimates)

Question 29

will a 99% confidence interval be wider or narrower than a 95% confidence interval?

Answer 29

wider

Question 30

will a 90% confidence interval be wider or narrower than a 95% confidence interval?

Answer 30

narrower

Question 31

pseudo-replication

Answer 31

the error that occurs when samples are not independent, but are treated as though they are ex: multiple heart rates measured from the same person and treated as different samples

Question 32

mutually exclusive

Answer 32

two events are mutually exclusive if they cannot both be true… Pr(A and B)=0

Question 33

addition principle

Answer 33

if two events A and B are mutually exclusive, then Pr(A or B)=Pr(A)+Pr(B)

Question 34

general addition principle

Answer 34

A and B don’t have to be mutually exclusive.

Pr(A or B)=Pr(A)+Pr(B)-Pr(A and B)

Question 35

probability distributions: discrete

Answer 35

probability is measured by the height of the bar

Question 36

probability distributions: continuous

Answer 36

probability is quantified by area under the curve

Question 37

independence

Answer 37

two events are independent if the occurrence of one gives no information about whether the second will occur

Question 38

multiplication principle

Answer 38

if two events A and B are independent, then Pr(A and B) =Pr(A) X Pr(B)

Question 39

Conditional probability

Answer 39

The conditional probability of an event is the probability of that event occurring given that a condition is met

Question 40

Positive Predictive Value

Answer 40

the probability that subjects with a positive screening test actually have the disease pr(d|+)