Classification of Data: Levels of Measurement

00:00 In our previous video, we distinguish between categorical and numerical data.

00:05 Furthermore, we saw that numerical data can be discrete and continuous.

00:10 It's time to move on to the other classification levels of measurement.

00:15 These can be split into two groups.

00:18 Qualitative and quantitative data.

00:20 They are very intuitive, so don't worry.

00:24 Qualitative data can be nominal or ordinal.

00:28 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.

00:38 They aren't numbers and cannot be ordered.

00:42 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 on unappetizing, neutral, tasty and delicious. Although we have words and not numbers, it is obvious that these preferences are ordered from negative to positive.

01:04 Thus, the level of measurement is qualitative ordinal.

01:09 Okay. So what about quantitative variables? Well, as you may have guessed by now, they are also split into two groups, interval and ratio.

01:21 Intervals and ratios are both represented by numbers, but have one major difference.

01:25 Ratios have a true zero, and intervals don't.

01:30 Most things we observe in the real world are ratios.

01:32 Their name comes from the fact that they can represent ratios of things.

01:37 For instance, if I have two apples, and you have six apples, you would have three times as many as I do.

01:45 How did I find that out? Well, the ratio of six and two is three.

01:51 Other examples are a number of objects in general distance and time.

01:58 All right. Intervals are not as common.

02:01 Temperature is the most common example of an interval variable.

02:05 Remember, it cannot represent a ratio of things and doesn't have a true zero.

02:10 Let me explain.

02:11 Usually, temperature is expressed in Celsius or Fahrenheit.

02:16 They are both interval variables.

02:18 Say today is five degrees Celsius or 41 degrees Fahrenheit and yesterday was ten degrees Celsius or 50 degrees Fahrenheit.

02:27 In terms of Celsius, it seems today is twice colder.

02:31 But in terms of Fahrenheit, not really.

02:35 The issue comes from the fact that zero degrees Celsius and zero degrees Fahrenheit are not true zeros.

02:42 These scales were artificially created by humans for convenience.

02:47 Now there is another scale called Kelvin, which has a true zero.

02:52 Zero degrees Kelvin is the temperature at which atoms stop moving, and nothing can be colder than zero degrees kelvin.

02:59 This equals -273.15 degrees Celsius or -459.67 degrees Fahrenheit.

03:09 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.

03:17 Celsius and Fahrenheit have no true zero and our intervals.

03:22 Finally, numbers like two, three, ten, 10.5.

03:26 I , etc.

03:27 Can be both interval or ratio, but you have to be careful with the context you are operating in. All right.

03:35 We've quickly gone through the types of data and the measurement levels.

03:39 Stick around and see the types of graphs that are used on a daily basis.