Stats

Question 1

Relationship between variance and s.d?

Answer 1

Sd^2 = Var

Question 2

Poisson?

Answer 2

E(X) = ;\
E(X^2) = ;\ + ;\^2
Var (X) = ;\

Question 3

Binomial?

Answer 3

E(X) = np 
Var(X) = npq

Question 4

Poisson as an approximation to the Binomial?

Answer 4

Used if n large and p small

Use ;\ = np

Question 5

Exponential?

Answer 5

f(x) = ;\e^-;\x

F(x) = P(Xx) = e^-;\ x

E(X) = 1
——
;\

Var(X) = 1
——
;\^2

Question 6

y on x?

Answer 6

Y = a + bx

Used if:
Predict x
X is a control variable

Question 7

x on y?

Answer 7

X = a + by

Used for:
Predict x for given y
If y is a control variable

Question 8

Pearsons product moment correlation?

Answer 8

Used for:
Scatter diagram elliptical shape
Normal bivariate date

‘r’ is a sample of the parent population ‘p’
“Where p is the correlation coefficient for the parent population”

Use:
p = / > / < / 0.5 etc

Question 9

Spearmans tank correlation coefficient?

Answer 9

Used for ranked data

Use +ve / -ve / no association

Question 10

Contingency Tables - Chi squared

Answer 10

Expected values using
Row total X column total
———————————-
Sample size

IF LESS THAN 5 COMBINE CATEGORIES

Chi squared values:
(O - E)^2
————-
E

Question 11

P values?

Answer 11

P val < sig val = Reject H0

P val > sig val = Accept H0

Question 12

Goodness of fit?

Answer 12

For binomial, maybe estimate a value for p: mean = np

For poisson, may have to estimate ;\

IN BOTH CASES -1 from V