Exploring Data

Question 1

What is a categorical varialbe?

Answer 1

variables that take on values that are names or labels, such as color, or breed of dog.

Question 2

What is a quantitative variable?

Answer 2

variables that are that are numerical, and represent a measurable quantity, like salary or height.

Question 3

How do we represent categorical variables?

Answer 3

With bar charts or pie charts

Question 4

How do we represent quantitative variables?

Answer 4

With histograms, stem and leaf plots, or boxplots

Question 5

When do we use the mean to describe a distribution?

Answer 5

When the distribution is unimodal and symmetric

Question 6

When do we use the median to describe a distribution?

Answer 6

When the distribution is not unimodal and symeetric.

Question 7

What is standard deviation?

Answer 7

The average distance from the mean

Question 8

What is a z score?

Answer 8

The number of standard deviations away from the mean

Question 9

What is percentile?

Answer 9

percent to the left

Question 10

What is the five number summary?

Answer 10

min, Q1, median, Q3, max

Question 11

What is IQR

Answer 11

interquartile range: Q3 - Q1

Question 12

What is the empirical rule?

Answer 12

mean-68-95-99.7–yes!!

Question 13

What percent of data lies above the median?

Answer 13

50%

Question 14

How do you determine “outliers”

Answer 14

1.5 IQR’s above Q3 or below Q1

Question 15

If a distribution is skewed right, which is higher, the median or mean?

Answer 15

the mean–the mean chases the tail!

Question 16

How do you know whether to use the mean and s.d. to describe data, or median and IQR?

Answer 16

If the data is unimodal and symmetric, use the mean and s.d., otherwise use median and IQR

Question 17

What should you remember when making graphs?

Answer 17

Label your axes, give a key if needed, and give the graph a name!

Question 18

How much data is between Q1 and Q3?

Answer 18

50%

Question 19

what is a contingency table

Answer 19

shows distributions across 2 variables like gender and music pref. AKA 2-way table

Question 20

How can you tell if variables in a contingency table are independent?

Answer 20

If the distributions are the same across the variables.. Then it doesn’t DEPEND.. so INDEPENDENT

Question 21

marginal distribution

Answer 21

overall distributions of a single variable in contingency table (out in margins)

Question 22

conditional distribution

Answer 22

A distribution within the table, along only one row or one column? NOT IN THE MARGINS

Question 23

How do you describe distributions (histograms)?

Answer 23

Shape-Cener-Spread- and STRANGE (Outliers and gaps) some say GSOCS. where’s yo GSOCS?

Question 24

If asked to compare distributions, what should you write about?

Answer 24

Compare Shapes, Centers, Spreads, and Stranges.. The GSOCS

Question 25

Give a simple example showing that adding a constant doesn’t change the spread, but changes the center. (this always happens)

Answer 25

Data set: 1,2,3,4,5 Spread(range): 5-1=4, Center: 3
add three and get new data set: 3,4,5,6,7 spread: still 4 Center: 5 (center went up, spread stayed the same). The IQR and SD will stay the same, but median and mean +3

Question 26

Give a simple example showing that multiplying by a constant changes both the spread and the center. (this always happens)

Answer 26

Data set: 1,2,3,4,5 Spread(range): 5-1=4, Center: 3
mult by three and get new data set: 3,6,9,12,15 spread:12 Center:9 (both center and spread were multiplied by three) IQR and SD will be multiplied by 3 and all values including Q1, median, etc.

Question 27

How do you describe center?

Answer 27

Talk about the mean (balance), median (splits area in half), mode (peaks? if bimodal, talk about both modes) or simply say: “centered around ____”

Question 28

How do you describe shape?

Answer 28

unimodal, bimodal, multimodal, uniform AND symmetric, skewed

Question 29

Spread description?

Answer 29

range, IQR, stand dev, variance, or simply say: “ From here to about here”

Question 30

what happens if you ADD a constant to each value in a data set?

Answer 30

it is SHIFTED only. This effects all of the data values and measures of center (mean, med) and quartiles, deciles, etc… IT DOES NOT CHANGE THE SPREAD! (IQR, St Dev, Range all stay the SAME).

Question 31

what happens if you multiply all of a data set by a constant?

Answer 31

it is scaled.. Everything is effected. Mean/ median/ stand dev/ iqr/ quartiles all multiplied by that constant. Center, spread and all individual values are changed.

Question 32

If you want to calculate % above a value, what do you put into normcdf(? ?)

Answer 32

find z score for value, and then normcdf (Z left, 999)

Question 33

Which calculator function gives you a z score?

Answer 33

invnorm(%ile)… YOU MUST USE PERCENTILE (%to left)

Question 34

What does normcdf do?

Answer 34

It gives you the area under the normal curve between any two z scores