Descriptive Statistics - University of Memphis

[Pages:29]CIVL 3103

Introduction to Descriptive Statistics

Learning Objectives

? To understand the goal of statistical methods of data analysis

? To apply multiple techniques (summary statistics, tables, graphics) to describe data, and to understand the benefits of each.

Uncertainty in Engineering

? Uncertainty is inherent in all real world problems.

? Two types of uncertainty: ? Natural randomness of underlying phenomena ? Inaccurate estimation of real-world parameters and conditions

? Statistics and probability are needed for describing information and forming the bases for design and

decision making under uncertainty.

Purpose of Probability/Statistics in Engineering

? The purpose of probability and statistics is to deal with uncertainty.

? Probability and statistics are widely used in engineering contexts to develop models or information that can be used in engineering decision-making so that the associated risks and costs are effectively managed.

Introduction to Descriptive Statistics

Descriptive vs. Inferential Statistics

DEFINITIONS

? Population ? all members of a class or category of interest ? Parameter ? a summary measure of the population (e.g.

average) ? Sample ? a portion or subset of the population collected as

data ? Observation ? an individual member of the sample (i.e., a

data point) ? Statistic ? a summary measure of the observations in a

sample

Populations and Samples

Population

Sample

Parameters

Inference

Statistics

Summary Statistics

? Measures of Central Tendency ? Arithmetic mean ? Median ? Mode

? Measures of Dispersion ? Variance ? Standard deviation ? Coefficient of variation (COV)

Measures of Central Tendency

8 6 4 10 3 8 4 8 5

The sample mean is given by:

The sample median is given by:

3 4 4 5

6

8 8 8 10

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