Calculating Mean / Variance - S1 Watch

Tulian
Badges: 0
Rep:
?
#1
Report Thread starter 7 years ago
#1
I have to estimate the mean and variance from a histogram, with no data values or boundaries given.

I'm given 2 histograms to look at:
one has a x axis range from 0 to 70 , with every 10 increments. The other is from 0 to 90 .

Couple of questions,
1) How would you know which set has the greater variance / mean just by looking at it ?
2) How would you estimate the mean / variance from one of the histogram given ?

+rep on offer , just not sure how to do this and would appreciate help
0
reply
ttoby
Badges: 15
Rep:
?
#2
Report 7 years ago
#2
(Original post by Tulian)
I have to estimate the mean and variance from a histogram, with no data values or boundaries given.

I'm given 2 histograms to look at:
one has a x axis range from 0 to 70 , with every 10 increments. The other is from 0 to 90 .

Couple of questions,
1) How would you know which set has the greater variance / mean just by looking at it ?
2) How would you estimate the mean / variance from one of the histogram given ?

+rep on offer , just not sure how to do this and would appreciate help
1) The one with the largest mean would be the one where roughly the 'middle' of the bars is at a higher x value, and the larger bars are generally at higher x values. From what you've said, it's likely that the one on the 0-90 scale would have a larger mean, but this depends where abouts the bars are positioned on this scale.

Varience is a measure of spread - the more spread out the data is the larger the varience. So if you had lots of bars of similar-ish height covering a large range of x values then that would have a larger varience. If the bars make a sort of spike within a small range of x values then that would have a smaller varience.

2) To estimate the mean, look at roughly where the middle of the clump of bars is, or where the tallest bar is.

Estimating the variance is harder to do by eye. One way of getting a rough estimate is to look at the bars and ask yourself - how far from the mean are the data values on average? This will give you an estimate of the standard deviation. Square this number to get the variance.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • Cranfield University
    Cranfield Forensic MSc Programme Open Day Postgraduate
    Thu, 25 Apr '19
  • University of the Arts London
    Open day: MA Footwear and MA Fashion Artefact Postgraduate
    Thu, 25 Apr '19
  • Cardiff Metropolitan University
    Undergraduate Open Day - Llandaff Campus Undergraduate
    Sat, 27 Apr '19

Have you registered to vote?

Yes! (314)
37.83%
No - but I will (64)
7.71%
No - I don't want to (62)
7.47%
No - I can't vote (<18, not in UK, etc) (390)
46.99%

Watched Threads

View All