lect 2 desctriptive and inferencial statts and CI

Question 1

what are descriptive statistics

Answer 1

statistics used by researchers to report on samples.

summarize information to speed up and simplify the comprehension of a population’s characteristics.

Question 2

how do descriptive techniqes organize data

Answer 2

tables

• freq distributiona
• relative frequency distrubutiona

graphs

• bar chart
• histogram
• boxplot

Question 3

how do descriptive stats summarize data

Answer 3

central tendency/ mid sample value (location)

• Mean
• Median
• Mode

variation summary diff w/in a groupm(spread)

• Range
• Interquartile range
• Variance
• Standard deviation

Question 4

what is the mean

Answer 4

average

add up values for each case and divide by total number of cases

Question 5

describe the median

Answer 5

• The middle value when a variable’s values are ranked in order
• point that divides a distribution into two equal halves
• if data are listed in order, point at which 50% of the cases are above and 50% below it
• The 50th percentile

Question 6

describe the mode

Answer 6

• the most common data point
• if all values are unique then there isnt one
• is not always at the centre of distribution
• can be multiple

Question 7

define the spread

Answer 7

the Variation of the recorded values on a variable

• larger spread has cases further from mean
• smaller spread has individual cases to the mean

Question 8

describe the range

Answer 8

distance, between the lowest and highest values of a variable.

highest value- lowest value.

Question 9

describe Standard deviation

Answer 9

• how much the members of a group differ from the mean value for the group.
• larger deviation = increased variation from mean
• equal to 0, only when all values are the same ( constant and not a “variable”).

Question 10

what happens to the mean When a constant is added to every observation

Answer 10

new sample mean is equal to original mean plus the constant.

Question 11

what happens to the standard deviation when a constant is added to every observation,

Answer 11

standard deviation is unaffected.

Question 12

what happens to the sample mean when every observation is multiplied by the same constant,

Answer 12

new sample mean is equal to original mean multiplied by the constant.

Question 13

what happens to the standard deviation when every observation is multiplied by the same constant,

Answer 13

new sample standard deviation is equal to original standard deviation multiplied by the magnitude of the constant.

Question 14

what is the normal distrubution

Answer 14

MEAN and SD are appropriate for histogram summary

bell shaped curve where the mean is at it’s peak

histogram: graphical display of data using bars of different heights

Question 15

what are the three rules of sigma when data has an approx normal distribution

Answer 15

approximately 68% of the data lie within one SD of
the mean

approximately 95% of the data lie within two SDs of
the mean

approximately 99.7% of the data lie within three SDs
of the mean

Question 16

what is the difference betw/ standard error of a mean & standard deviation

Answer 16

when the mean estimates individual values standard deviation = the degree of uncertainty by which the mean estimates individual values

when the mean estimates the population mean standard error of mean = the degree of uncerntainty with which the mean estimates the population mean

Question 17

what is the confidence interval of the mean

Answer 17

a range of values around the mean where we expect the “true” population mean is located.

µ=x+/-1.96xSEM

example

• X = 9.5 years; SD = 2.8 years

SEM = 0.5 years

95% level of confidence => Z = 1.96

µ = 9.5 ± (1.96 x 0.5) = 9.5 ± 1 years

95% CI for µ is (8.5; 10.5 years)