Accuracy and Precision

accuracy and precision to words we use

we're describing data and measurements

but they mean very different things even

though in everyday speech we tend to use

interchangeably so in this video we're

going to talk about the difference

between accuracy and precision and how

we can use them when we're making

measurements let's use an example of a

game from a carnival or a State Fair

okay it's called guess my age here's how

it works you may have seen it done

before there's somebody standing up and

they usually pick somebody who it's not

very easy to howl them okay and then if

you want to play it you gather around

and you write down on a piece of paper

how old you think the person is okay now

there's a prize or a series of prizes

and the prize goes to the person who can

most closely guess the age of the the

person who's standing up there okay so

let's go ahead and look at a game right

here of guess my age okay we're at a

State Fair we're enjoying our fried

Oreos and our funnel cake and we go over

and we look at someone who's standing

standing in front of this this pavilion

or whatever okay and there are a bunch

of people and they write down their

different guesses for this person's age

okay one person says 20 another person

says 52 another says 18 32 30 and 45

okay so these are the six guesses for

the age of this person who's going to

win well first of all we have to know

actually the age of the person up there

and then we have to figure out who's

closest or whose answer has the greatest

accuracy so accuracy is a fancy word

that means how close you are to the

actual value okay

so let's say that the actual value is 30

that this guy's age is actually 30 let's

look at these choices in terms of

accuracy all right well the the person

who guessed 30 they're going to win

because they got it right

but let's look at these other choices so

30 I'm going to right here perfect it's

incredibly accurate because 30 is as

close as you can get to the actual value

32 they were they were off by two years

so I'll say that a 32 is 2 away 20 is 10

Dawei and 52 here is a 22 years away 45

is 15 years away and 18 is going to be

12 years away

so let's rank these guys in terms of

accuracy 30 is the most accurate 32

would be the the second most accurate

it's two away the next is going to be 20

because that's 10 away then we have 18

which is 12 years off 45 which is 15

years off and this guy here at 52 which

is 20 years 22 years off okay so actual

age 30 and accuracy is how close we are

to the actual value greatest accuracy

least accuracy okay now there's another

term that's not going to win you any

prizes at a State Fair and that's called

precision but it's just just as

important so precision is about how

consistent a series of values are with

each other and it has nothing to do with

whether those values are right whether

they're accurate

doesn't matter how close they are the

actual value okay let me show you right

let's say we get a group of four people

playing guess my age and we each have

them write down the age on a piece of

paper okay and we get we get four

guesses of the age 29 31 30 and 30 these

are the four guests okay so to ask about

precision we want

ask the question how consistent are

these guys with each other they're

pretty close they're they're pretty

consistent we've got twenty nine thirty

thirty thirty-one so we'll say that

these guys are definitely pretty precise

okay and then we can ask the question

are they accurate well if they're

accurate as we said before they're very

close to the actual value now this guy's

age is actually 30 and 29 30 31 these

guys are all pretty close to 30 so we'll

also say that if these are accurate

let's look at some other examples here


let's um let's say that we get another

four people to play this game and they

give the the following answers 55 55 55

and 54 are the four guesses for the age

all right now these are way off in terms

of accuracy but the question is are they

precise well they're very consistent

with each other 355 s and 154 so precise

I'm definitely going to say yes but

accuracy are they accurate no they're

nowhere near the actual age which is

thirty so we say no so things can be

precise if they're close together and

consistent but accurate not at all

let's look at another example here

another four people come and play guess

my age and here are the guesses that

they make one person says he's 25

another says he's 45 mother says he's 60

and another says he's 19 let's look at

these definitions all right are these

answers precise are they close together

are they consistent not at all right we

have everything from 19 all the way up

to 60 scatter all over the place so are

they precise

no absolutely not and additionally let's

look at accuracy

are they accurate are they close to the

actual value absolutely not we have

everything from 19 to 60 we didn't get

anywhere near 30

so we'll say these are neither precise

nor are they accurate now when it comes

to accuracy and precision teachers and

textbooks often like to make an analogy

um where they were they where they put a

bull's eye and have some sort of a

target analogy so let's talk through

that right now here I have some some

very very poorly draw bull's eyes here

and let's go and look at these uh first

examples that I had all right with these

for ages 30 29 30 31 okay using this

target analogy we could say that a guess

that's exactly accurate would be a

bull's eye right so 30 would be a bull's


so we've got two 30 s that are right

close here and then we've got a 29 and a

31 which are not very far away okay so


they're really close the bull's eye and

precise they're all consistent so

they're very close together so this is

what a bull's eye target representation

of accurate and precise would look like

okay so now let's take a look at an

example that is precise but it's not


this was the one where everybody guessed

that this guy was in his mid-50s okay so

if 30 if the target is the actual age

these guys are way off here like maybe

this is 55 but they're all very close

together so all of our hits are going to

be far away from the target but close

together so here we have accurate no

nowhere near the center but precise yes

because they're all together now finally

let's look at the example where these

numbers are neither precise nor are they

accurate again 30 here indicates hitting


on the nose right here in the bullseye

alright we've got one guy at forty five

another who misses the bullseye in the

other direction nineteen one who says

sixty one who says twenty five okay so

the point is these kids are all over the


there are nowhere near the center which

would be the actual value nor are they

close together so they're not accurate

and they're not precise so in the next

videos we'll go over how we can actually

do measurement problems with these

accuracy and precision concepts that

we've learned but for right now this

should give you a good idea of the

conceptual basics of accuracy and