PO218 Statistics Midterm

Question 1

The 6 descriptive measures

Answer 1

• Frequency
• Intervals
• Proportion
• Percentage
• Ratio
• Visualization

Question 2

Proportion (p)

Answer 2

the fraction of the case distribution
- always in between 0 and 1

Question 3

Data visualization

Answer 3

graphics that display information in a meaningful way

Question 4

The 2 main categories of descriptive measures

Answer 4

Central tendency and Variation / Dispersion

Question 5

Central tendency

Answer 5

most typical or representative value of a data set
- 3 measures: mean, median, and mode

Question 6

Mean (average)

Answer 6

For continuous variables
- sum ➗ number of cases
- population mean: represented by µ
- sample mean: represented by x (with a line on top)

Question 7

Median (midpoint)

Answer 7

For continuous or ordinal variables
- sort the data set and select the middle number (average of middle 2 numbers if even data set)

Question 8

Mode (most frequently occuring)

Answer 8

For nominal or ordinal variables
- the value with the most number of cases

Question 9

Variation / Dispersion

Answer 9

how a variable is either concentrated or spread out

Question 10

The 5 measures of variation

Answer 10

• Standard deviation
• Range
• Index of qualitative variation
• Coefficient of variation
• Variation ratio

Question 11

Standard deviation

Answer 11

for continuous variables
- how far a certain score is from the mean

Question 12

Range

Answer 12

for continuous and ordinal variables
- difference between the highest and lowest value
- range = highest value - lowest value

Question 13

Index of qualitative variation

Answer 13

for nominal and ordinal variables
- 0 to 1
- 0 = no variation
- 1 = variable is split evenly among categories

Question 14

Coefficient of variation

Answer 14

for continuous variables

Question 15

Variation ratio

Answer 15

for ordinal and nominal variables
- based on mode (most)
- 0 to 1
- 0 = no variation
- 1 = highest variation
- if vr > 0.5, the mode is questionable

Question 16

Probability

Answer 16

the chance that an event will occur
- 0 = no chance
- 1 = guaranteed chance

Question 17

Central limit theorom

Answer 17

the larger the sample size, the more accurate the result will reflect the population

Question 18

z scores

Answer 18

Standard deviations based on the standard normal
- when to use: if the population variance is known, or the sample size is bigger than 30
- positive z score = above the mean
- negative z score = below the mean

Question 19

Reliability factors for z scores

Answer 19

• 1.645 accounts for 90% of the area
• 1.96 accounts for 95% of the area
• 2.575 accounts for 99% of the area
• 3.3 accounts for 99.9% of the area

Question 20

t scores

Answer 20

Standard deviations based on the ‘t’ distribution
- when to use: when the population standard deviation is unknown, or the sample size is below 30

Question 21

Margin of error

Answer 21

the difference between the sample statistic and the population parameter

Question 22

Standard normal

Answer 22

• Upper limit: sample statistic + (reliability level) (standard of error)
• Lower limit: sample statistic - (reliability level) (standard of error)

Question 23

Deviant/outlier

Answer 23

a case or score that doesn’t follow the normal distribution (which means it isn’t cause and effect related)

Question 24

Type 1 error

Answer 24

rejecting a correct null hypothesis

Question 25

Type 2 error

Answer 25

accept an incorrect null hypothesis

Question 26

Alpha level

Answer 26

probability of committing a type 1 or type 2 error

Question 27

Null hypothesis

Answer 27

the expected mean of a variable

Question 28

Alternative hypothesis

Answer 28

stating that the expected mean is not the null hypothesis