Chapter 1 Flashcards Preview

Biostatistics > Chapter 1 > Flashcards

Flashcards in Chapter 1 Deck (52)
Loading flashcards...
31

Standard deviation

Measures spread by caluculating how far the observations are from their mean--> should only be used when the mean is chosen as the method of center

32

n-1

Degrees of freedom of the variance or standard deviation

33

S=0

Only when ther is no spread--> means all the observations have the same value, otherwise S is greater than 0

34

What does it mean if the standard deviation is higher?

S gets larger when the observations are more spread out across their mean

35

Units

S has the same units of measurement as the original observation

36

S and the Mean

Like the mean, S is not resistant a few outliers or strong skewness can greatly increase S

37

How do you measure risk in finance

Taking a looking at the standard deviation of returns --> large spread --> less predictable--> more risky
BUT five number summary would be more informative

38

Density curve

A density curve is a mathematic model for the distribution of a quantitative variable

39

What does a density curve describe?

The overall pattern of a distribution. Thea area under the curve AND within any range of values is the proportion of all observations that fall within that range

40

68-95-99.7 rule

68% of observations fall within 1 standard deviation of the mean
95% of observations fall within 2 standard deviations of the mean
99.7% of observations fall within 3 standard deviations of the mean

41

Z-Score

Standardized value--> tells us how many standard deviations the observation falls away from the mean and in which direction

42

Z-score positive

Observations larger than the mean

43

Z-score negative

Observations smaller than the mean

44

Sample survey

Collects data from a sample of cases that represent a larger population of cases

45

Observation vs Experiment

We do not attempt to influence the responses by imposing a treatment (change)

46

Training Data Set

In some studies we generate one set of data to generate a set of results
Ex. model to predict something

47

Database

Data sets for statistical analysis can be extracted

48

Data warehouse

System for organizing, storing, and analyzing complex data

49

Sampling frame

A list of items to be sampled

50

Response rate

The proportion of the original sample who actually provide usable data

51

Undercoverage

Some groups in the population are left out of the process of choosing the sample

52

Nonresponse

Occurs when a case chosen for the sample cannot be contacted or does not cooperate