Sampling Distributions

Sampling Distributions
l From a given population we can take series of
different samples and calculate a sample statistics (eg.,
sample mean ) for each sample.
l Properties of Sampling Distribution of Means:
1). The mean of sampling distribution is similar to
population mean ?
2). SD of the distribution of the sample means is equal
to
This is called SE of the mean, It is measured the
variability of mean of the samples.
3). Provided n is large enough, the shape of the
sampling distribution is approximately normal. The best
estimate of the population standard error of the
mean, , is
n
s
s = x
n
s
s = x
(n ³ 30)
x s
PDF created
Just as is normal deviate that refers to normal distribution of Xi values,
l is a normal deviate referring to normal distribution of
means (X values).
l Example: The mean and standard deviation of systolic blood pressure for normal
men are 130 and 9 mm Hg respectively, what is the probability of drawing from
them a random sample of 9 measurements which has a mean,
l 1- Less than 125 mm Hg?