1.7 Biostatistics 1

Question 1

What is a probability sample?

Answer 1

A probability sample is one that is chosen in a way that allows you to determine how likely it is that an individual from the population is included in the sample.

Question 2

What are the methods for getting probability samples?

Answer 2

Simple random sampling
Systematic sampling
Stratified sampling
Cluster sampling

Question 3

Describe ‘Simple Random Sampling’

Answer 3

Every individual in the population has an equal chance of being part of the sample

Question 4

Describe ‘Systematic Sampling’

Answer 4

Sample chosen from a list of al individuals in the population by selection every k^th individual, where k is any number. e.g. every 3rd person from the list. May inadvertently develop a pattern in sample.

Question 5

Describe ‘Stratified Sampling’

Answer 5

The population is divided into strata (subgroups) and then a random sample is selected from each of the strata. Usually stratify for age and sex.

Question 6

Describe ‘Cluster Sampling’

Answer 6

Clusters (groups) are selected from the population, and then a random sample of the individuals is taken form each of the selected clusters. May introduce some sort of bias (e.g. socio-economic status when clustering by streets or suburbs)

Question 7

What is a ‘Non-Probability Sample’

Answer 7

A non-probability sample is one that is chosen in a way that makes it impossible to determine how likely it is that an individual from the population is included in the sample.

Question 8

What are the four methods for getting non-probability samples?

Answer 8

Convenience Sampling
Quota Sampling
Purposive Sampling
Snowball Sampling

Question 9

Describe ‘Convenience Sampling’

Answer 9

Asking med student to participate in research

Question 10

Describe ‘Quota Sampling’

Answer 10

Med students recruited until quota for each gender is filled

Question 11

Describe ‘Purposive Sampling’

Answer 11

Selecting individuals that exemplify the ‘typical med student’

Question 12

Describe ‘Snowball Sampling’

Answer 12

Select a few ‘typical med students’ who ask their friends to join and so on.

Question 13

Name the two types of data

Answer 13

Categorical

Numerical

Question 14

Name the two types of categorical data

Answer 14

Nominal

Ordinal

Question 15

Name the two types of numerical data

Answer 15

Discrete

Continuous

Question 16

Describe Nominal Data

Answer 16

Numbers mean nothing, purely a way to name data. E.g. gender (Male = 1, Female = 2)

Question 17

Describe Ordinal data

Answer 17

Some sort of rationale/ranking to numbering. e.g. In general, how do you rate your health? 1=poor, 2=fair and so on.

Question 18

What are the three measures of central tendency?

Answer 18

Mean
Median
Mode

Question 19

Describe the Mean

Answer 19

Sum of values / number of values.
Can be manipulated algebraically, most stable estimate of central tendency. However, is influenced by extreme scores and can’t be used for nominal data

Question 20

Describe the Median

Answer 20

Middle point of ordered data (50% of scores fall either side). Relatively unaffected by extreme scores (useful for skewed distributions), can be used with ordinal data. However cannot be manipulated algebraically.

Question 21

Descrive the Mode

Answer 21

The value that occurs most frequently in the data set. Can be used with nominal data, is a real score from the data set. However, may not be particularly representative of the data set and cannot be manipulated algebraically.

Question 22

What are the 5 measures of variability?

Answer 22

Range
Interquartile range
Variance
Standard deviation
Standard error

Question 23

How do you calculate the variance?

Answer 23

s^2.
Calculate the mean, subtract mean from each observation, square the difference. Sum the squared differences and divide by n-1. Not directly interpretable as variance can fall outside the values of the range.

Question 24

How do you calculate standard deviation?

Answer 24

Square root of the variance.
Conveys how widely or tightly the observations are distributed from the central tendency (mean). A measure of variance that is on the scale of the mean.

Question 25

How do you calculate Standard Error?

Answer 25

SE=SD/Square root of n. Often confused with standard deviation. Describes the variability we might expect in the means of repeated sample taken form the population. Quantifies variation in sample means.

It assumes the data is taken from one sample of an infinite number of possible samples from larger population.

Question 26

In a normal distribution, what percentage of values lie within one standard deviation either side of the mean?

Answer 26

68%

Question 27

In a normal distribution, what percentage of values lie within two standard deviations either side of the mean?

Answer 27

95%