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## Lecture/Week 2

by: Mackenzie Thompson

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2

# Lecture/Week 2 MARB 303

Mackenzie Thompson
Texas A&M

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This is chapter/lecture 2 that will be on the exam
COURSE
Biostatistics
PROF.
Dr. Hui Liu
TYPE
Class Notes
PAGES
2
WORDS
CONCEPTS
Biostatistics
KARMA
25 ?

## Popular in Ecology, Evolution, and Marine Biology

This 2 page Class Notes was uploaded by Mackenzie Thompson on Monday September 5, 2016. The Class Notes belongs to MARB 303 at Texas A&M University taught by Dr. Hui Liu in Fall 2016. Since its upload, it has received 4 views. For similar materials see Biostatistics in Ecology, Evolution, and Marine Biology at Texas A&M University.

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Date Created: 09/05/16
Lecture 2 Descriptive Statistics – Central Tendency Measures of Central Tendency  All measures are concerned with capturing a single number that represents the typical case of measure of data  Each measure has pros and cons and some are more appropriate than others given different levels of measurement o Pay attention to these strengths and weaknesses and to the appropriate usage  Arithmetic Mean o The well known and most frequently used measure of central tendency is the mean or average (technically the arithmetic mean)  Mean is the sum of the measurements divided by the number of observations  Frequency Data o Frequency: counts of the number of observations in a category o Relative frequency: Frequency divided by the total number of observations in the data set o When summarizing a dataset, list all values in order  Potential Issues of the mean o One of the potential drawbacks to the mean is that it can be significantly impacted by extreme values or outliers  The median o The value that divides the distribution of data into 2 equal parts  If there is an odd number  middle observation is median  If there is an even number  median is the average of the 2 middle values  List values in order  Not impacted by outliers  Mean vs. Median o Mean:  Used with continuous variables  Uses all the data (more information)  More stable given repeated sampling  More easily manipulated o Median  Used with continuous or ordinal variables  Unaffected by outliers  Mode o The mode is the vale that occurs most frequently  There can be bi-modal, tri-modal, or multi-modal distributions  Can be used for all levels of measurement  A distribution with only one peak (i.e. with one value occurring the most) then mode would be right under the peak  Connection o For a normal, bell-shaped distribution:  All measures of central tendency are the same value  As the distribution diverges from normality, the values will differ o Skewed distributions:  Left side is higher  positively skewed  Right side is higher  negatively skewed

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