basic statistics

Question 1

define descriptive statistics

Answer 1

stats that summarise otherwise confusing, large, complicated amounts of information. normally in the form of graphs or tables.

Question 2

define inferential statistics

Answer 2

shows relationships between population and samples, used to draw conclusion.

Question 3

what is anecdata ?

Answer 3

data with no real context and thus limiting its usefulness.

Question 4

name the four types of descriptive statistics ?

Answer 4

nominal, ordinal, interval, ratio.

Question 5

describe nominal data

Answer 5

• qualitative
• no natural order
• e.g. female/male , cat/dog
• can only show if phenomenon is present or not.
• a =/ b

Question 6

describe ordinal data

Answer 6

• values can be ranked
• e.g. bronze/silver/gold , level/gcse
• a > b

Question 7

describe interval data

Answer 7

• distance between values has meaning
• ratio not relevant
• 0 not well defined
• e.g. change in temperature
• a-b

Question 8

describe ratio data

Answer 8

• fractions are meaning full
• 0 is meaning full
• 0 means an absence of phenomenon
• e.g. height, weight, volume, speed, time
• a/b

Question 9

describe cross sectional data

Answer 9

• one observation per ( person, household, firm, country )
• no time dimension
• order of observation doesn’t matter

Question 10

describe time series data

Answer 10

• one observation per time period ( day, week, quarter, month, year )
• order of observation does matter

Question 11

describe pooled cross sectional data

Answer 11

this is when there is a set of two cross sectionals together

Question 12

describe longitudinal or panel data

Answer 12

-following the same subject over different times

Question 13

define discrete data

a. finite

b. countably infinite

Answer 13

a. bounded clear countable options. (i.e. age, agree/disagree, age)
b. infinite number of options but countable ( i.e. wealth, income)

Question 14

which type of data is most common in economics ?

Answer 14

finite data

Question 15

describe continuous data

Answer 15

measured on the number line, uncountable infinite options ( i.e. time, distance )

Question 16

describe a histogram

Answer 16

• similar to a bar chart but with equal even class/bar widths
• height = frequency / class width
• height = frequency density

Question 17

how do you construct a frequency polygon ?

Answer 17

you draw a histogram and place marks in the middle of the top of the bar charts and draw them together.

Question 18

how do you determine how data is skewed ?

Answer 18

• when the mean is on the left of the peak ( negative / leftward skewed )
• when the mean is on the right of the peak ( positively / rightward skewed )

Question 19

what is rounding bias ?

Answer 19

when the data is less accurate because the observes like to round their observations ?

Question 20

what are these averages ?

a. mode ( ungrouped )
b. mode ( grouped )
c. mean ( ungrouped )
d. mean ( grouped )
e. median ( ungrouped )
f. median ( grouped )

Answer 20

a. most common observation, could be multi modal and when this occurs its not a very useful descriptor of the data
b. look at frequency density not just frequency
c. sum of values/number of observations
d. sum of class midpoint x class frequency / number of obs total
e. n/2 for even number chose in-between value

f. (( L + N/2 - B ) / G )X W 
L = lower boundary of median class 
B = cumulative frequency of the groups before the med group 
W = group width 
G = frequency of the median group

Question 21

what is the expected value operator ?

Answer 21

predicts, if we were to select a random stat : what would it say ? normally equal to the mean

Question 22

how do you calculate

a. quartiles
b. quintiles
c. deciles
d. percentiles
e. inter quartile range

Answer 22

a. n/4 x X
b. n/5 x X
c. n/10 x X
d. n/100 x X
e. 3rd quartile - 1st quartile

Question 23

how do you calculate variance for

a. population
b. sample

Answer 23

a. sum of ; x - mean squared
divided by n

b. same as ^ but sample mean and divided by n-1 instead

Question 24

how do you calculate standard deviation ?

Answer 24

it is the square root of variance

Question 25

how does this transportation affect data ?

a. DATA + Y
b. DATA x X

Answer 25

a. range of y normal 
   variance of y normal 
   expected + y
b. range x X 
    variance x X^2
    expected x X

Question 26

how do you calculate a Z score ?

Answer 26

(test value - population mean) / standard deviation