1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
Lubov Fominskaja [6]
3 years ago
10

How to find standard deviation from percentile for normal distribution?

Mathematics
1 answer:
QveST [7]3 years ago
8 0
The standard deviation of what?  Percentiles from any normal distribution look the same, just like the unit normal, so you can't really determine the standard deviation of the original scores. You can determine a z score from a percentile.  That tells us the number of standard deviations, positive or negative, a given score is away from the mean score.  It's a normalized test result.

Your percentile is (a hundred times) the probability that another score is less than your score.  We have a normal distribution, so that probability is the integral of the standard normal from negative infinity to our normalized score.  

Let's call the percentile rank p, already scaled between zero and 1.

p=.5 corresponds to a z score z=0 because the fiftieth percentile means we got an exactly average score, 0 standard deviations away from the mean.

We know 68% of the probability will be between -1 and +1 standard deviation.  So z=-1 corresponds to p=.5-.68/2=.16 and
z=1 corresponds to p=.5+.68/2=.84

Similarly, 95% of the probability will be between -2 and +2 standard deviations.  So z=-2 corresponds to p=.5-.95/2=.025 and
z=2 corresponds to p=.5+.95/2=.975

That's about the list I can do off the top of my head. I think three standard deviations is 99.7%. For the rest we just consult a z table or integrated normal table.  We find p in the body of the table (maybe |.5-p| depending on the table) and then the column headings tell us our z score.

In this modern age, your computer can do this for you quickly

You might be interested in
The area of a square is 64 cm. what is the length of one side of the square?
Citrus2011 [14]

Answer:

8cm

Step-by-step explanation:

Since the area of a square is Side X Side (s x s) it is also s². The s² is also equivalent = 64cm². To find the length of a side you do the √64cm² and you get 8cm for a side. Great Job!

5 0
4 years ago
Ms. Blevins wants to survey a random sample of students at her middle school about the amount of homework assigned each night. W
NeTakaya
I think maybe 3) would make the most sense because she wants a random sample of students and the other options are specific on the type of students.
6 0
3 years ago
Could a triangle have lengths of the sides of 4,8,6,2
Brilliant_brown [7]

Answer:

no

Step-by-step explanation:

triangles can only have 3 side lengths

8 0
3 years ago
Write an expression for the cost per person if five friends share the cost of a dinner equally.
Leto [7]

Answer:

Let c=cost of dinner, 5=the # of people, and P=the cost of person

P=C/5

b. P = (1000)/5

P = 200

Step-by-step explanation:

8 0
3 years ago
How do you get the numbers 4 5 13 to equal 5
MAVERICK [17]
You can subtract 4 from 13 then subtract 4 again
3 0
4 years ago
Other questions:
  • Find the X intercept of the graph of the linear function X equals 1/2 X +3
    7·1 answer
  • Can someone please help me?
    13·1 answer
  • Circle the error and explain why it is an error<br><br> Please help ASAP thank you!
    14·1 answer
  • Which fraction has a repeating decimal as its decimal expansion?
    9·2 answers
  • Anyone good with algebra 1?
    10·1 answer
  • Use the diagram to find the measure of each angle.
    7·1 answer
  • How is 9644 divided by 4
    10·2 answers
  • What is the equation a line passes through the points p(2,4) q(-1,3)​
    12·1 answer
  • Rick was given a 15% tip waiting on a table of customers who ordered $60.00 in food and drinks. How much did Rick earn in tips f
    7·1 answer
  • Hey guys did I get any of these right, if not pls help me.
    14·2 answers
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!