Chap 1 Section 2Chap 1 Section 2

Ogives and TimeplotsOgives and Timeplots

O-What???O-What???

OgivesOgives

Pronouced Oh-JivesPronouced Oh-Jives

An ogive is a relative cumulative frequency An ogive is a relative cumulative frequency graph.graph.

Frequency: how often a value is Frequency: how often a value is representedrepresented

Relative: percentRelative: percent

Cumulative: less than or equal toCumulative: less than or equal to

Ogive: percentilesOgive: percentiles

Frequency TablesFrequency Tables

This data set lists the This data set lists the number of books that number of books that are on the desks of are on the desks of 50 college students at 50 college students at 8:00 a.m. on Monday 8:00 a.m. on Monday morning. Using this morning. Using this data, count how many data, count how many times each value times each value occurs. Make a tally occurs. Make a tally chart.chart.

33 55 1010 44 66

77 22 1212 1111 99

77 55 33 44 88

55 1010 99 1414 77

22 11 00 55 77

88 99 1414 1818 1010

11 66 77 88 55

33 1010 1212 33 44

22 22 66 44 33

55 1010 99 99 66

Frequency and Relative FrequencyFrequency and Relative Frequency

Frequency simply means how many times Frequency simply means how many times a certain value occurs. a certain value occurs.

Relative frequency means you convert the Relative frequency means you convert the number of tally marks to a percent of the number of tally marks to a percent of the total.total.

Cumulative Frequency vs. Relative Cumulative Frequency vs. Relative Cumulative FrequencyCumulative Frequency

Cumulative frequency, therefore, tells us how Cumulative frequency, therefore, tells us how many values fall at or below a certain number!many values fall at or below a certain number!

Relative cumulative frequency divides that Relative cumulative frequency divides that number by the total in the data set to give us a number by the total in the data set to give us a percentile. This tells us the percent of values percentile. This tells us the percent of values that fall at or below a certain number!that fall at or below a certain number!

To have your calculator find the cumulative To have your calculator find the cumulative frequency, go to List, OPS, Cumsum( frequency, go to List, OPS, Cumsum(

Cumulative Frequency Graph

0

10

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0 5 10 15 20

Number of Books

Cu

mu

lati

ve F

req

uen

cy

Relative Cumulative Frequency Graph

0%

20%

40%

60%

80%

100%

120%

0 5 10 15 20

Number of Books

Rel

ativ

e C

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tive

Fre

qu

ency

This is an Ogive!!!These are percentiles

Turn to page 36. Turn to page 36.

We will work through 1.29We will work through 1.29

Time PlotsTime Plots

The time scale is on the horizontal axis.The time scale is on the horizontal axis.

The variable of interest (temperature, The variable of interest (temperature, stock prices, gasoline prices) is on the stock prices, gasoline prices) is on the vertical axis.vertical axis.

Look for trends and an overall pattern.Look for trends and an overall pattern.

Section 1.2 Comparing DistributionsSection 1.2 Comparing Distributions2005’s Free Response Question #1 part a

The back-to-back stem plot below displays the number of calories of food consumed per kg of body weight for each student…

a) Write a few sentences comparing the distribution of daily caloric intake ….

How it was graded:How it was graded:Part a) was graded Essentially Correct, Partially Part a) was graded Essentially Correct, Partially Correct, or IncorrectCorrect, or IncorrectE: a student must successfully E: a student must successfully comparecompare center, center, shape shape andand spread. Specific numeric values are spread. Specific numeric values are not not requiredrequired..P: a student must successfully P: a student must successfully comparecompare 2 of the 3 2 of the 3 measures of center, shape and spread.measures of center, shape and spread.All other responses are graded as Incorrect. Stating All other responses are graded as Incorrect. Stating “the mean of the rural students’ daily caloric intake “the mean of the rural students’ daily caloric intake is 40.45 is 40.45 whilewhile the mean for the urban students is the mean for the urban students is 32.6” is not a COMPARISON and would earn an I.32.6” is not a COMPARISON and would earn an I.

Graph Choices for Comparing Graph Choices for Comparing Categorical DistributionsCategorical Distributions

For two qualitative data sets, a side by side bar For two qualitative data sets, a side by side bar graph is effective.graph is effective.

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