collection of numerical data 

AND

collection, analysis, interpretation 

or explanation, and presentation of 

numerical data.

consists of methods 

dealing with the collection, tabulation, 

summarization, and presentation of data

onsists of methods 

that permit one to reach conclusions and 

make estimates about populations based 

upon information from a sample

all members of a class or category of 

interest

 enumeration or evaluation of all 

members of a populatio

– a summary measure of the individual 

observations made in a census

 a summary measure of the individual 

observations made by evaluation of a sampl

5 reasons Why Should Engineers 

Study Statistics?

Statistics enables one to:

1. Present and describe numerical information properly

2. Draw conclusions about large populations from sample 

information

3. Improve processes (engineer quality into a product)

4. Properly design experiments and model physical 

relationships

5. Obtain reliable predictions of real-world responses

collection of related 

categorical or numerical information

a characteristic that can take 

different values (ex. temperature, height, 

cost)

a characteristic that has a 

fixed value (ex. pi, e – natural log)

only 

whole number values (countable values, 

such as the number of students in a 

class; number of planes departing an 

airport in an hour)

represent 

numerical measurements on a 

continuous scale (ex. length, weight, 

age)

variables based 

on counts or proportions (number of 

times an event occurs, % of defective 

items, etc.)

continuous 

variables such as time, height, weight, 

etc.

Defines a characteristic of an object or 

event by a specific criterion that is 

precisely the same to different 

individuals and will remain the same 

over time

Not a vague description that may be 

interpreted differently by different 

individuals

 Coffee is too hot to drink if it is 

warmer than 180 degrees Fahrenheit.

The time it takes to make a cake is 

measured from the time the first 

ingredient is added to the mixing bowl 

until the cake is cooked

Cost – cheaper to 

study a small group 

than all individuals

Time – less time to 

collect/analyze data

Accuracy – smaller 

data sizes reduce the 

opportunity for “human 

errors” when compiling 

data

Feasibility – it is not 

practical, nor possible 

(in the case of 

destructive testing) to 

study a complete 

population

Scope of information –

can gather more 

information per 

individual when fewer 

individuals are studied

a sample in 

which the probability or chance of 

selecting an element from the 

population is known

 not as 

scientifically rigorous, used when a 

probability sample is not possible or 

cost effectiv

 All elements of a population have an 

equal chance of being included in the 

sampl

a member of a 

population can be represented more than 

once (ex. in a random drawing for various 

door prizes, the winners’ names are put 

back into the “pot” after each drawing)

a member 

of a population can only be represented 

once (ex. you can only win one door prize –

your name is not returned to the “pot”)

based on easy 

availability of members of a population (“take 

what you can get”)

– member selection based on 

the opinion or judgment of some expert

sample members based on 

characteristics judged to be important to the 

study (ex. if 10% of the population is known to 

be left-handed, 10% of the sample will be 

chosen to be left-handed)

Advantages

Convenient

Speedy

Lower cost

Good for rough 

approximations such 

as for pilot 

investigations

Disadvantages

Lack of accuracy due to 

bias

Limited generalization of 

results possible

– fitness for use

 Defined by the needs, expectations, 

perceptions, and experience of the 

customer 

“Beauty is in the eye of the beholder

What is the

PDCA Cycle?

Useful for process improvement, a.k.a. 

quality improvement

Plan Do Check Act