Interpreting Data

Question 1

What are the main 2 types of data?

Answer 1

• qualitative

- quantitative

Question 2

What are the 2 types of quantitative data?

Answer 2

• discrete (involves whole numbers)

- continuous (information measured on a continuum/scale)

Question 3

What are the 3 measures of location?

Answer 3

• median (number in the middle of a set of numbers, used when there are large outliers or skewed data)
• mode (most common number)
• mean (average)

Question 4

What are the 2 measures of spread?

Answer 4

• standard deviation

- interquartile range (when large outliers or skewed date)

Question 5

What is Gaussian distribution?

Answer 5

Normal distribution
No outliers
Use mean and standard deviation

Question 6

How does the Gaussian distribution change if the mean and standard deviation change?

Answer 6

Mean changes = graph moves left or right

S.d. changes = graph moves up or down (if it decreases graph increases) but area under line remains the same

Question 7

What is a standard error?

Answer 7

Measure of statistical accuracy of an estimate
Standard deviation of the distribution of all possible sample means
Standard error of the mean = standard deviation/√sample size

Question 8

How is the confidence interval ranges calculated?

Answer 8

Sample mean ± 1.96 x standard error

- get 2 values

Question 9

What does confidence interval mean?

Answer 9

Expect the confidence interval amount of samples to be between the calculated range
- as sample size increases confidence interval gets narrower but range stays the same

Question 10

What is the correlation coefficient?

Answer 10

• between -1 and 1
• 1 = perfect positive correlation
• -1 = perfect negative correlation

Question 11

What is the significance of linear regression?

Answer 11

Y = a + bx
Y - outcome (dependent variable)
x - predictor (independent variable)
b - slope
a - intercept

Question 12

What is statistical significance?

Answer 12

observed sample difference between groups may be due to chance

• statistically significant means unlikely due to chance
• determined by p value and confidence interval

Question 13

How is the confidence interval calculated?

Answer 13

mean difference ± 1.96 x SE of mean difference

Question 14

What is the confidence interval?

Answer 14

• mean difference and SE mean difference between 2 groups

Question 15

What is the p value?

Answer 15

• probably of observing a result as or more extreme of the sample result if the underlying assumption in the population is true
• if greater than 0.05 (5%) cannot rule out chance effect
• if less than 0.05 probably not chance

Question 16

How do you calculate standard deviation?

Answer 16

Average distance from the mean
(Value - mean)^2 for each, add up and divide by number of values
square the answer

Question 17

What is the interquartile range?

Answer 17

Difference between 75th centile - 25th

- median is 50th

Question 18

For a Gaussian distribution what are the reference ranges?

Answer 18

99% ranges lie within 2.58 SDs
95% ranges lie within 1.96 SDs from the mean
90% ranges lie within 1.64 SDs from the mean

Question 19

When do we use standard deviation and when do we use standard error?

Answer 19

• s.d for ranges (individual values)

- SE for confidence intervals (means)

Question 20

As sample size increases how does the range and confidence interval change?

Answer 20

Range stays the same

Confidence interval gets narrower

Question 21

How do we determine whether an observed difference was due to chance?

Answer 21

Look at confidence intervals and p values

Question 22

What are the 2 types of qualitative data?

Answer 22

• nominal (unordered)

- ordinal (ordered)

Question 23

What are the 2 types of nominal data?

Answer 23

• binary (dead or alive)

- categorical (colours)

Question 24

Define reference ranges

Answer 24

A constant proportion of values lying within any specified number of standard deviations above or below the mean

Question 25

How do you calculate reference range?

Answer 25

mean ± 1.96 x standard deviation

Question 26

What is the relationship between confidence intervals and p values?

Answer 26

If 99% CI for a difference excludes 0 then p<0.01, includes 0 then p ≥ 0.01
95% - excludes 0 then p<0.05, contains then p≥0.05
90% - excludes 0 then p<0.1, contains then p≥0.1