Download Finding Standard Error

Finding Standard Error
Standard error
• The standard error is the standard deviation of a
sampling distribution – we have three types of
standard errors:
• Standard error of the mean – used with one
sample
• Standard error of the difference between the
means – used with independent samples
• Standard error of the mean of the differences –
used with dependent or paired samples
One sample
sm = standard error of the mean
• S = standard
deviation
• n = number of
participants
• Find the standard
deviation of the
sample, divide by the
square root of N
s
sm 
n
Two Independent Samples
Sm1-m2=Standard error of difference between the means
• Find Standard deviation of each separate
sample (S1 and S2)
• Pool(average) standard deviations
S pooled
(df1 )( s12 )  (df 2 )( s22 )

df1  df 2
•Standard error of Difference between the means
sm1m 2  s pooled
1
1

n 1 n2
Paired or Dependent Samples
Standard error of mean of differences
First member
Differences
A1
Second
member
A2
B1
B2
B1-B2
C1
C2
C1-C2
D1
D2
D1-D2
E1
E2
E1-E2
A1-A2
Paired or Dependent Samples
Standard error of mean of differences
Smd
• We work with the
Differences
• Smd = standard error of
mean of differences
• Sd = standard deviation of
the differences
• n = number of pairs
S md
sd

n pairs