Download presentation

Presentation is loading. Please wait.

1
**Statistical Reasoning for everyday life**

Intro to Probability and Statistics Mr. Spering – Room 113

2
**“Top of the Muffin to you!” ?????**

4.3 Measures of Variation “Top of the Muffin to you!” ????? Variation: Describes how widely data are spread out about the center of a distribution. ????How would you expect the variation to differ between the running times of theatre movies compared to running times for television sitcoms???? Theatre movie times more variation Television sitcoms less variation usually 30 or 60 minutes

3
**4.3 Measures of Variation How do we investigate variation?**

Study all of the raw data… Range… Quartiles… Five-number summary (BOXPLOT or BOX-and-WHISKER)… Interquartile range… Semi-quartile range… Percentiles… MAD… Variance & Standard Deviation…

4
**4.3 Measures of Variation Today: 65th Percentile! Semi-quartile range…**

MAD… Variance & Standard Deviation… MAD???

5
**4.3 Measures of Variation Semi-quartile range**

The semi-quartile range is another measure of spread. It is calculated as one half the difference between the Upper Quartile (often called Q3) and the Lower Quartile (Q1). The formula for semi-quartile range is: (Q3–Q1) ÷ 2. Since half the values in a distribution lie between Q3 and Q1, the semi-quartile range is one-half the distance needed to cover half the values. In a symmetric distribution, an interval stretching from one semi-quartile range below the median to one semi-quartile above the median will contain one-half of the values. However, this will not be true for a skewed distribution. The semi-quartile range is not affected by higher values, so it is a good measure of spread to use for skewed distributions, but it is rarely used for data sets that have normal distributions. In the case of a data set with a normal distribution, the standard deviation is used instead. We will discuss standard deviation later.

6
**4.3 Measures of Variation (Q3–Q1) ÷ 2**

EXAMPLE: Find the Semi-quartile range of the data. Semi-quartile = 4.1, 5.2, 5.6, 6.2, 7.2, 7.7, 7.7, 8.5, 9.3, 11.0 Q1 = 5.6 Q3 = 8.5 Semi-quartile = (8.5 – 5.6) 2 = 1.45 (Q3–Q1) ÷ 2

7
**4.3 Measures of Variation Percentiles**

The nth percentile of a data set is (an estimate) of a value separating the bottom values from the top (100 – n)%. A data value that lies between two percentiles is often said to lie in the lower percentile. You can approximate the percentile of any data value with the following formulas:

8
4.3 Measures of Variation EXAMPLE: Percentiles. What percentile is the lowest score, Q1, Q2, Q3, and highest score? 4.1, 5.2, 5.6, 6.2, 7.2, 7.7, 7.7, 8.5, 9.3, 11.0 Lowest number = 0 percentile Q1 = 5.6 = 25th percentile Q2 = ( )/2 = 7.45 = 50th percentile Q3 = 8.5 = 75th percentile Highest number = 100th percentile

9
**4.3 Measures of Variation What percentile is the 9.3?**

EXAMPLE: Percentiles. What percentile is the 9.3? 4.1, 5.2, 5.6, 6.2, 7.2, 7.7, 7.7, 8.5, 9.3, 11.0 9.3 is the 9th number out of ten, after the numbers are set in ascending order. Therefore, it is larger than 9 out of ten numbers, or the 90th percentile. Note: One quartile is equivalent to 25 percentile while 1 decile is equal to 10 percentile and 1 quintile is equal to 20 percentile Think about it: P25 = Q1, P50 = D5 = Q2 = median value, P75 = Q3, P100 = D10 = Q4, P10 = D1, P20 = D2, P30 = D3, P40 = D4, P60 = D6, P70 = D7, P80 = D8, P90 = D9

10
**4.3 Measures of Variation MAD: Mean Absolute Deviation**

MAD is the mean of the absolute differences between the “sample mean” and the data values.

11
4.3 Measures of Variation Example: Find the MAD (Mean Absolute Deviation). DATA: 10, 1, 3, 3, 3, 4, 5, 6, 5, 10 Mean = 5 ∑ 5, 4, 2, 2, 2, 1, 0, 1, 0, 5 = 22 MAD = 22/10 = 2.2

12
**4.3 Measures of Variation Variance Variance…**

The variance of a random variable is a measure of statistical dispersion/distribution found by averaging the squared distance of its possible values from the mean. Whereas the mean is a way to describe the location of a distribution, the variance is a way to capture its scale or degree of being spread out. The unit of variance is the square of the unit of the original variable. Variance

13
**4.3 Measures of Variation Example: Find the Variance.**

DATA: 10, 1, 3, 3, 3, 4, 5, 6, 5, 10 Mean = 5 ∑ 25, 16, 4, 4, 4, 1, 0, 1, 0, 25 Variance (s2) = 80/9 = 8 8/9 ≈ 8.89

14
**4.3 Measures of Variation Standard Deviation…**

Universally accepted as the best measure of statistical dispersion/distribution. Standard deviation is developed because there is a problem with variances. Recall that the deviations were squared. That means that the units were also squared. To get the units back the same as the original data values, the square root must be taken.

15
**4.3 Measures of Variation Example: Find the Standard Deviation**

DATA: 10, 1, 3, 3, 3, 4, 5, 6, 5, 10 Mean = 5 ∑ 25, 16, 4, 4, 4, 1, 0, 1, 0, 25 Variance (s2) = 80/9 = 8 8/9 ≈ 8.89 Standard Deviation = = ≈ 2.981

16
**4.3 Measures of Variation The Range Rule of Thumb…**

The is approximately related to the range of distribution by the following: We can use this rule of thumb to estimate the low and high values: low value ≈ mean – 2 × standard deviation high value ≈ mean + 2 × standard deviation The range rule of thumb does not work well when low and high values are extreme outliers. Therefore, use careful judgment in deciding whether the range rule of thumb is applicable.

17
**4.3 Measures of Variation The Range Rule of Thumb… EXAMPLE:**

The mean score on the mathematics SAT for women is 496, and the standard of deviation is Use the range rule of thumb to estimate the minimum and maximum scores for women on the mathematics SAT. low value ≈ mean – 2 × standard deviation = 496 – (2×108) = 280 minimum high value ≈ mean + 2 × standard deviation = (2×108) = 712 maximum Is this reasonable? Of course, scores below 280 and above 712 are unusual on SAT’s.

18
**4.3 Measures of Variation HOMEWORK: Pg 174 # 3 Pg 175 # 9, 10, and 14**

Pg 176 # 24, pg 176 # all (Letters c, d only)

Similar presentations

OK

Lecture 5 Dustin Lueker. 2 Mode - Most frequent value. Notation: Subscripted variables n = # of units in the sample N = # of units in the population x.

Lecture 5 Dustin Lueker. 2 Mode - Most frequent value. Notation: Subscripted variables n = # of units in the sample N = # of units in the population x.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To ensure the functioning of the site, we use **cookies**. We share information about your activities on the site with our partners and Google partners: social networks and companies engaged in advertising and web analytics. For more information, see the Privacy Policy and Google Privacy & Terms.
Your consent to our cookies if you continue to use this website.

Ads by Google

Ppt on inhabiting other planets in the milky Ppt on five monuments of india File type ppt on cybercrime prevention Ppt on carbon cycle in nature Ppt on means of transport free download Ppt on plants for grade 4 Ppt on conservation of momentum video Ppt on unit and non unit fractions Ppt on review of related literature in research Ppt on school management system