Dear Madan,

 

Thanks a lot for clearing by doubt about probability and frequency distribution!! As far as the second question is concerned I am sorry for not making the question clear. Here is what I wanted.

I have a population of the weights of 1000 people. In order to determine the sample mean I go through the following process. I am confused as to which of the two processes is the correct one :

1) Population (1000)
2) Take some observed values (say, 10)
3) Find its mean
4) Repeat the process from step 2 till you get a sample of means (at least 30 such steps is to repeated from step 2 so that we get a normal distribution of the sample mean i.e keep taking 10 values from the population and find its mean; do it 30 or more times)

OR

1) Population (1000)
2) Take a sample of at least 30 or more (say, 45)
3) Find its mean
4) Repeat step 2 (I do not know how many times) till you get a normal distribution.

I wanted to clarify which is the right process and how many observed values and sample values is required.

Thanks for your help

Regards

Viv

 

On 9/18/06, Madan Gopal Kundu <Madan.Kundu@... > wrote:

Dear Viv,

 

I cannot understand your question clearly. So I am trying to answer your second query.

<< What is the fundamental difference between
probalility distruibutions and frequency distributions?>>

 

Probability distribution: Values of random variable with corresponding probabilities

Frequency distribution: Values of random variable with corresponding frequencies.

 

Example: Let X be a random variable. Also assume that x is a particular value of X and f(x) and p(x) be the frequency (of x) and probability (that X takes value x) respectively. That means,

p(X=x) =Probability ( X=x)

f(x)= Frequency of x

 

      x           f(x)        p(x)

--------------------------

0                    2            2/10=0.2

1                    1            1/10=0.1

2                    3            3/10=0.3

3                    0            0/10=0.0

4                    4            4/10=0.4

  -------      -------        --------

Total           10               1.0

 

Here {x, f(x)} will be known as frequency distribution of random variable X

Whereas {x, p(x) } will be known as probability distribution of random variable X

 

Hope it helps.

 

Regards,

MADAN

 

 

---

From: Statisticians_group@... [mailto:Statisticians_group@...] On Behalf Of vivranga
Sent: 18 September 2006 11:06
To: Statisticians_group@...
Subject: [Statisticians_group] Confusion!!

 

I am new to stats and have a couple basic questions regarding
sampling , the central limit theorem and probability.

If the sample size is 30 or greater then the sample means follow a
normal distribution.I wanted to know the minimum size of the
observations in each sample and its limits. Can I take 30 samples
each having 2 observations with the knowledge that the means of
these samples would follow a normal distribution?

Also I would like to get an intuition about probability
distributions. What is the fundamental difference between
probalility distruibutions and frequency distributions?

Can anyone please let me know about these as I am not able to
progress much without getting my basics clear :-)

Thanks

Viv

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