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Question 1

categorical variable

Answer 1

a categorical variable is placed an individual into one of several groups or categories

Question 2

quantitative variable

Answer 2

a quantitative variable has numerical values and it makes sense to find the average value

Question 3

association

Answer 3

there is an association between two variables if knowing the value of one variable helps predict the value of the other

Question 4

mean

Answer 4

average value of the observation

Question 5

median

Answer 5

midpoint of the values, also called Q2

Question 6

first third quartiles

Answer 6

Q1 has about one-fourth of the observations below it, and Q3 has about three fourths of the observations below it

Question 7

interquartile range

Answer 7

IQR is the range of middles 50% of the observations IQR =Q3-Q1

Question 8

standard Deviation

Answer 8

measures the typical distance of the values in a distribution from the mean

Question 9

variance

Answer 9

average squared deviation

Question 10

shape

Answer 10

typical shapes of a distribution are roughly symmetric, skewed left and skewed right

Question 11

center

Answer 11

mean for roughly symmetric distributions, median for skewed distributions

Question 12

spread

Answer 12

standard deviation for roughly symmetric distributions, IQR for skewed distributions. Range = man-min as a last resort

Question 13

transforming data by add/subtract a

Answer 13

measure of center (median and mean) and location (quartiles and percentiles) change by a measure of spread don’t change

Question 14

transforming data by multiply/ divide b

Answer 14

measure of center, location, and spread change by b

Question 15

Density curve mean and median

Answer 15

the mean is the balance point of the curve. The median divides the area under the curve in half

Question 16

uniform distribution

Answer 16

a distribution that takes constant height over some interval of values

Question 17

68-95-99.7 rule

Answer 17

percent of observations that lie within one tow and three standard deviations of the mean in a normal curve

Question 18

normal probability plot

Answer 18

if the normal probability plot is roughly linear, then the data is apporiximately normal
if the normal probability is not roughly linear then the data is not approximately normal

Question 19

scatterplot

Answer 19

displays the relationship between two quantitative variables measured on the same individuals

Question 20

explanatory variable, factor, response variable

Answer 20

if we think that a variable x may help explain, predict or even cause changes in anohter variable y, we call x an explanatory variable and y a response variable

Question 21

correlation r

Answer 21

meaures the direction and strength

r has no units, is between -1 and +1 and is not the value of the slope

Question 22

correlation and causation

Answer 22

correlation does not imply causation, no matter how strong there may be other confounding variables

Question 23

least squares regression line

Answer 23

the straight line y hat = a+bx that minimizes the sum of the squares of the veritcal distances of the observed points from the line

Question 24

slope b

Answer 24

b is the predicted change in y when x increases by 1 unit in context

Question 25

y intercept a

Answer 25

predicted resonse y hat value when the explanatory variable x equals 0, in context

Question 26

extrapolation

Answer 26

avoid extrapolation the use of a regression line for prediction using values of the explanatory variable outside the range of the data

Question 27

residual

Answer 27

y- y hat the difference between the observed and predicted values of y

Question 28

influentials

Answer 28

outliers that substantially change the correlation or the regression line's slope or y intercept

Question 29

census

Answer 29

census collects data from every individual in the population

Question 30

convenience sample

Answer 30

choose individuals who are easiest to reach

Question 31

voluntary response sample

Answer 31

individyals choose to join the sample in response to an open invitation key terms phone in survey, TV survey

Question 32

simple random sample

Answer 32

SRS uses chance prosses to give every possible sample of a given size the same chance to be chosen. choose an srs by labeling the members of the population and using slips of paper, technology or random digits table to select the sample

Question 33

stratified random sample

Answer 33

divide the population into strata, groups of individuals that are similar in some way that might affect their responses. Then choose a separate SRS form each stratum and combine these SRSs to form the sample

Question 34

cluster sample

Answer 34

divide the population in clusters, groups of individuals that are located near each other. Randomly select some of these clusters.. All the individuals in the chosen clusters are included in the sample

Question 35

undercoverage

Answer 35

when some members of the population cannot be chosen to be in the sample

Question 36

reponse bias

Answer 36

when a systematic pattern of inaccurate answers leads to resonse bias

Question 37

nonresponse bias

Answer 37

when people can't be contacted or refuse to answer

Question 38

wording bias

Answer 38

wehn confusing or leading questions introduce stron gbias

Question 39

observational study

Answer 39

gathers data on individuals as they are

Question 40

experiment

Answer 40

deliberatly imposes treatments on experimental units

Question 41

experimental units

Answer 41

each of the individuals to which treatments are applied. Human experimental units are called subjects

Question 42

confounding

Answer 42

variables are confounded whe their effects on a response variable can't be distinguished from that of the explanatory variable

Question 43

completely randomized design

Answer 43

all experimental units are assigned to the treatments completely by chance

Question 44

placebo

Answer 44

a fake treatment for the control group. That prevents confounding due to the placebo effect, in which some patients get better because they expect the treatment to work.

Question 45

double blind experiment

Answer 45

neither the subjects nor those interacting with them and measuring their responses know who is receiving which treatment. If one party knows and the other doesn't then the experiment is single blind

Question 46

randomized block design

Answer 46

use blocks of experimental units that are similar with respect to a variable that is expected to affect the response. Treatments are assigned at random within each block. Responses are then compared within each block and combined with the reponses of other blocks after accounting for the differences between the blocks

Question 47

matched pairs design

Answer 47

in some matched paris designs, each subject receives both treatments in a random order. in others, two very similar subjects are paired, and the two treatments are randomly assigned within each pair

Question 48

mutually exclusive and independence

Answer 48

if two events are mutually exclusive, they cannot also be independent

Question 49

probabilty distribution

Answer 49

the probabilty distribution of a random variable gives its possible values with gaps between

Question 50

continuos random variable

Answer 50

a continuous random variable x takes all values in an interval of numbers. the probability distribution of x is described by a density curve. The probability of any event is the area under the density curve and above the values of x that make up the even

Question 51

population parameter/ sample statistics

Answer 51

a parameter is a number that descrives a population. To estimate an unknown parameter, use a statistic calculated from a sample

Question 52

sampling distribution

Answer 52

the sampling distribution of a statistic a statistic describes the values of the statistic in all possible samples of the same size from the same population

Question 53

unbiased estiamator

Answer 53

a statistic is an unbiased estimator if the center (mean) of its sampling distribution is equal to the true value of the parameter