Scale of Measurement

Survey Design Tips

Level of Measurement

• How much information a variable conveys about the difference among values

• The higher the level of measurement, the more information is conveyed

• The level of measurement determines what kind of statistics can be used

Levels of Measurement

NominalNominal OrdinalOrdinal IntervalInterval RatioRatio

Low HighMore Information

Nominal Variable

• Values are qualitatively different from each other

• “Qualitative” Variable

• “Naming/Labeling” Variable

• There is no particular way that values should be ordered

Example: Nominal Variable

GENDER• Values: Men /

Women• • Men and Women are

qualitatively different

• Cannot say which is better or higher

Example: Nominal Variable

Entree• Values: Meat, Fish,

Veggie• Meat, Fish and

Veggie are just different

• Reorder values in any way

Ordinal Variable

• Values are different from each other not in quality but in magnitude

• Values can be ordered , e.g., High to low, small to large, good to bad, etc.

• “Ranking variable” • “Ordering variable”

• Distance between values are not consistent

Example: Ordinal Variable

Course Grade• Values: A, B, C, D, F • A is higher than B, B is

higher than C, etc.

• The order is meaningful –

• Difference between B and C may not be equal to the distance between D and F

Interval/Ratio Variable

• Values are different from each other in quantity

• Values have a meaningful order and the distance between values are consistent

• “Quantitative” “Number” variable

• Interval Variable = Arbitrary Zero

• Ratio Variable = Meaningful Zero

Example: Interval Variable

IQ Test Score• IQ 120 is higher than

IQ100

• Difference between IQ 100 and 120 is the same as difference between IQ 80 and IQ 100

• IQ zero does not mean no point or no intelligence

Example: Interval Variable

Temperature (F)• 80F is higher than 60F

• Difference between 60F and 80F is the same as difference between 40F and 60F

• 0 F does not mean “no temperature”

Example: Ratio Variable

Weight • 200 lb. is heavier than 100 lb.

• Difference between 100 lb. and 200 lb. is the same as difference between 200 lb. and 300 lb.

• 0 lb. means you have NO weight

Example: Ratio Variable

Income ( in $) • $50K is more than $30K.• Difference between $50K

and $30K is the same as difference between $50K and $80K

• $0 income means you have NO income

Why “Equal Distance” Matters?

• If the distance between values are equal, you are able to calculate (add, subtract, multiply, divide) values

• You can get a mean only for interval/ratio variables

• You can use wider varieties of statistics for interval/ratio variables

Summary

Ratio

Interval

Ordinal

Nominal

Difference

Order

Equal Interval

Meaningful Zero

Calculate

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Level of Measurement

Altering Levels of Measurement

• You can measure the same object at different levels of measurement

• If you measure a variable at the higher level, you can transform it into the lower level variable

Example: Income

What was the amount of your income last year?

US $ __________

Did your annual income exceed US $5K last year?

1.Yes

2.No

What was the amount of your income last year?

1. Less than $3K

2. $3.1K - $5K

3. $5.1K - $10K

4. More than $10K

RatioOrdinalNominal

Let’s Think ….

• Height (in inches)• Color of eyes (black, brown, blue ..)• Size of Soda (S, M, L)• Menu at Taco Bell (Soft taco, Crispy taco,

Nachos, ..)• Commuting time (in minutes)• Class standing (freshman, sophomore..)• Major (FAMR, Fashion merchandise, …)• Dress size (5, 7, 9…)

Variable and Values

Age

0, 1, 2, …. 20, 21, 22, …, 40, 41, 42, ….60,

61, 62, ….

Variable

Values

Variable and Values

Gender

Male

Female

Variable

Values

What do you need to do or consider to design a good survey?

Before Designing your questionnaire

• Review research questions and hypotheses

• Clear definition of what you are studying

• Clear operational definitions for the attitudes or behaviors being studied.

Designing your questionnaire

• Writing items – and REWRITING ITEMS

• Well-constructed items are easier to summarize, analyze, and interpret than poorly constructed ones.

• Pay now, or pay later!

• Open ended (not answered by one word.. – Example: What do you think about the

UH parking situation?

• Restricted or close-ended– Example: – Parking around campus is

1 2 3 4 5 6 7

Difficult to find Easily available

• (example) Where do you drink?• At home____ In bars____ At parties____

In restaurants____

• Partially open-ended item– Other, specify____________

• Rating scale 1 - 10

• Scale Recommend 7 points with extreme word anchors

• Graphic line

• Keep items simple

• Avoid biased wording

• No abbreviations

• Don’t phrase with negative– Should students not drink soft drinks for breakfast?

Yes No– Better: Should students drink soft drinks for

breakfast? Yes No• Best: How often should students drink soft drinks for

breakfast?

1 2 3 4 5 6 7

Never Always

• Your questionnaire should elicit responses you are most interested in without a lot of extra info

• Organize items on questionnaire

• Pilot test !!!

• Assess reliability and validity

• Revise questionnaire

Ethics

• Guarantee anonymity of your participants and confidentiality of their responses.

• Anonymity

• Guarantee that there will be no way for the participants’ names to be associated with their answers or their survey.

Ethics continued

• Confidentiality

• Guarantee to not disclose any data in individual form, even if you know which participants go with which surveys.

• Data are reported in group form only.