CAL 1

Question 1

What is the definition of standard deviation

Answer 1

Standard deviation is a measure of how scattered the data is

Question 2

What does a probability distribution describe

Answer 2

describes how a value will change when measured on a group of people

Question 3

what shape does a normal distribution have

Answer 3

bell shaped curve

Question 4

What does the mean correspond to on the normal distribution curve

Answer 4

the highest point

Question 5

what properties does the normal distribution have

Answer 5

68% of all values lie within 1 standard deviation above and below the mean
90% of all values lie within 1.64 standard deviations below and above the mean
95% of all values lie between 1.96 standard deviations below and above the mean

Question 6

How do you work out the upper and lower bound (the 68% range)

Answer 6

Lower bound = Mean - Standard deviation
Upper bound = mean + Standard deviation
- the answers that you get for these are the answers that are in 68% of the range
- mean that below the lower bound is 16% of figures and above the upper bound is 16% of figures

Question 7

how do you work out the upper and lower bound for the 90% range

Answer 7

Lower bound = Mean - (1.64 x standard deviation)
Upper bound = Mean + (1.64 x Standard deviation)

• the answers that you get for these are the answers of the 90% range, range that 90% of figures fall in to
• below the lower bound 5% of figures fall
• above the upper bound 5% of figures are

Question 8

How do you work out the upper and lower bound for the 95% range

Answer 8

Lower bound = Mean - (1.96 x standard deviation)
Upper bound = Mean + (1.96 x Standard deviation)
- the answers that you get for these are the answers of the 95% range, the range that 95% of figures fall into
- below the lower bound 2.5% of figures fall
- above the upper bound 2.5% of figures are

Question 9

what range is the widest, 68%, 90% or 95%

Answer 9

95%

Question 10

What is the standard error

Answer 10

a measure of spread of the mean value from a group of sample

Question 11

How do you work out the standard error

Answer 11

standard deviation/ square root of n (n is the number of people in the study)

Question 12

what is the confidence interval

Answer 12

95% confidence interval = mean +/- (1.96 x Standard Error)

Question 13

what confidence interval is the widest out of 68, 95, 99%

Answer 13

99%

Question 14

how do you calculate the 68, 95 and 99% confidence interval

Answer 14

+/- means upper and lower boundaries, - for lower bounds and plus for upper boundaries

68% = mean +/- (1 x Standard error)
95%  = mean +/- (1.96 x Standard Error)
99% = mean +/- (2.58 x Standard Error)

Question 15

a decreasing standard deviation makes the curve …

Answer 15

tighter and closer together

Question 16

if the standard deviation remains the same and the mean decreases the curve…

Answer 16

remains the same shape

- moves towards the left

Question 17

if the standard deviation increases and the mean remains the same …

Answer 17

the 95% range becomes wider

Question 18

What is a confidence interval for the difference in means used

Answer 18

used to say whether the difference between two groups is statistically different or not

Question 19

How do you calculate the confidence interval for the difference in means

Answer 19

95% interval = difference in means +/- (1.96 x standard error of difference)

Question 20

what does standard error of difference equal

Answer 20

the square root of the standard error of group 1 plus the square root of the standard error of the other group

Question 21

why is a difference not significantly different

Answer 21

the confidence interval equals 0

- indicates no difference between the two groups

Question 22

what can changes in the placebo group be caused by

Answer 22

chance 
placebo effect
effect of time 
other effects
- the real group can also be caused by all of these and the actual effect of the stimulus

Question 23

How do you make the standard error for the difference in changes

Answer 23

add the standard error of the two groups together

Question 24

what is the mean change in the between two groups

Answer 24

mean of groups 1 - mean of group 2

Question 25

What is a P value

Answer 25

the p-value or probability value is the probability of obtaining test results at least as extreme as the results actually observed during the test, assuming that the null hypothesis is correct

Question 26

if the P value is less than 0.05% what does this mean

Answer 26

enough evidence to show something is biased or chance

Question 27

what is a two sided P value

Answer 27

A two-tailed test will test both if the mean is significantly greater than x and if the mean significantly less than x.

Question 28

How does sample size effect P value

Answer 28

if the difference in mean and standard deviation are the same, increasing the sample size decreases the P value

Question 29

the smaller the mean…

Answer 29

the bigger the sample size needed to show that the P value is not due to chance alone

Question 30

If the sample size increases but the mean and standard deviation remain the same, the confidence mean gets wider, true or false?

Answer 30

false