Original subtitles

Instructor: In our previous video,

we distinguished between categorical and numerical data.

Furthermore, we saw that numerical data

can be discrete and continuous.

It's time to move on to the other classification,

levels of measurement.

These can be split into two groups:

qualitative and quantitative data.

They are very intuitive, so don't worry.

Qualitative data can be nominal or ordinal.

Nominal variables are like the categories

we talked about just now, Mercedes, BMW, or Audi,

or like the four seasons,

winter, spring, summer, and autumn.

They aren't numbers and cannot be ordered.

Ordinal data, on the other hand,

consists of groups and categories

which follow a strict order.

Imagine you have been asked to rate your lunch

and the options are disgusting, unappetizing,

neutral, tasty, and delicious.

Although we have words and not numbers,

it is obvious that these preferences

are ordered from negative to positive.

Thus, the level of measurement is qualitative, ordinal.

Okay, so what about quantitative variables?

Well, as you may have guessed by now,

they are also split into two groups, interval and ratio.

Intervals and ratios are both represented by numbers,

but have one major difference.

Ratios have a true zero and intervals don't.

Most things we observe in the real world are ratios.

Their name comes from the fact

that they can represent ratios of things.

For instance, if I have two apples and you have six apples,

you would have three times as many as I do.

How did I find that out?

Well, the ratio of six and two is three.

Other examples are a number of objects in general,

distance, and time.

All right, intervals are not as common.

Temperature is the most common example

of an interval variable.

Remember, it cannot represent a ratio of things

and doesn't have a true zero.

Let me explain.

Usually, temperature is expressed in Celsius or Fahrenheit.

They are both interval variables.

Say today is five degrees Celsius or 41 degrees Fahrenheit

and yesterday was 10 degrees Celsius

or 50 degrees Fahrenheit.

In terms of Celsius, it seems today is twice colder,

but in terms of Fahrenheit, not really.

The issue comes from the fact that zero degrees Celsius

and zero degrees Fahrenheit are not true zeros.

These scales were artificially created

by humans for convenience.

Now, there is another scale called Kelvin

which has a true zero.

Zero degrees Kelvin is the temperature

at which atoms stop moving

and nothing can be colder than zero degrees Kelvin.

This equals minus 273.15 degrees Celsius

or minus 459.67 degrees Fahrenheit.

Variables shown in Kelvins are ratios

as we have a true zero and we can make the claim

that one temperature is two times more than another.

Celsius and Fahrenheit have no true zero and are intervals.

Finally, numbers like two, three, 10, 10.5, pi, et cetera,

can be both interval or ratio, but you have to be careful

with the context you are operating in.

All right, we've quickly gone through the types of data

and the measurement levels.

Stick around to see the types of graphs

that are used on a daily basis.