L3: Statistics

Question 1

Purpose of Statistics

Answer 1

used to investigate data to form opinion and gain information

Question 2

Mean (x)

Answer 2

measures center of distribution, strongly influenced by high values

Question 3

Median

Answer 3

middle value of list of values, not affected by outlier values

Question 4

Mode

Answer 4

number that occurs the most in a set of values

Question 5

Quartiles

Answer 5

splits data into quarters (25% of data below 1st quartile, 25% above 3rd quartile)

Question 6

Range

Answer 6

maximum - minimum value

Question 7

interquartile range

Answer 7

(Q3-Q1) is measure of spread

Question 8

Variance (s^2)

Answer 8

average of the squares of deviations of observation

Question 9

Symmetry

Answer 9

comparing mean and median (symmetrical: mean = median = mode)

Question 10

positive skewness

Answer 10

many low values & proportion of high values

Question 11

negative skewness

Answer 11

many high values & proportion of low values

Question 12

why use graphical tool?

Answer 12

presents ungrouped data in orderly fashion to show useful information, to highlight and understand data significance

Question 13

what are some graphical tools?

Answer 13

Histogram, cumulative frequency/probability plot, box plot

Question 14

Equally weighted average

Answer 14

average value of contaminant concentration over large area/volume

Question 15

Outlier

Answer 15

Observation that appears to be inconsistent with the rest of the data

Question 16

How to identify outlier

Answer 16

compare w/trend, use statistical and spatial presentation

Question 17

What to do w/ outliers?

Answer 17

keep them unless there is no reason to, outliers deserve further attention, may lead to new discovery