Variation

Question 0

What is observation?

Answer 0

Actual data result in front of you

Question 1

What is tendency?

Answer 1

True or underlying trend or relationship

Question 2

Relationship between observation and tendency?

Answer 2

Observed is best estimate of true tendency. Testing hypothesis to do so

Question 3

What is a hypothesis?

Answer 3

A statement that an underlying tendency of scientific interest takes a particular quantities value.

When testing the hypothesis, use and state the null as your hypothesis.

Question 4

What is calculated probability?

Answer 4

P-value

Question 5

What does a small p-value indicate?

Answer 5

Hypothesis is incompatible

Question 6

If p-value equal to or below 0.05?

Answer 6

Reject hypothesis (null) at 95% confidence level as observations are statistically significant hence data is inconsistent with the hypothesis and strong evidence against hypothesis.

At P=0.05, there is 5% chance that it is due to chance (the null) whereas 95% chance that A and B are connected. 0.05 is the cut off, hence a lower p-value the better.

Question 7

Is p-value > 0.05?

Answer 7

This does not prove the null hypothesis (even is P=0.999), just can not reject null hypothesis.

There is a greater than 5% chance that the effect is due to chance hence significant value

Question 8

Bones to pick about p-value?

Answer 8

P<0.05 is arbitrary as nothing much changed
Sample size affects it
Statistical significant not alway clinically relevant

Question 9

What is the 95% confidence interval?

Answer 9

We can be 95% sure that the true value of any measure lies between
(Observed value/error factor) - (Observed value X error factor)

Question 10

How to calculate error factor for incident rate or prevalence rate?

Answer 10

2(square root (1/d))
e

d= events observed in population

Question 11

How to calculate error factor for incidence rate ratio?

Answer 11

2(square root (1/d1 + 1/d2))
e

d1 & d2= events observed in each population

Question 12

How to calculate error factor for SMR?

Answer 12

2(square root 1+O)
e

O= observed number of events in population

Question 13

Method to doing an IRR and statistical relevance question?

Answer 13

State you H0 - null that there is no difference

IR for both group

IRR to give value X

Error factor of value X

Upper and lower CI

H0 is the value 1, hence if 1 features in CI there is

insufficient evidence to reject the null hypothesis as we can not say with confidence that men are more likely to have a stroke than women as p>0.05

Question 14

Define cohort study?

Answer 14

Group of people with know exposures / personal characteristics

Question 15

Process of concurrent cohort studies?

Answer 15

Start with 2 groups disease free people of same characteristics. 1 group with exposure, the other without.

Follow up over time for set period of time.

Calculate IRR and how many & which diseases occurs in p-y form.

Analyse and interpret

Question 16

What is another name for concurrent?

Answer 16

Prospective

Question 17

What is the historical cohort study process?

Answer 17

Start with 2 groups disease free people of same characteristics. 1 group with exposure, the other without. Classify initial exposure using records

Follow up using historical records until a set time.

Calculate IRR and how many & which diseases occurs in p-y form.

Analyse and interpret

Question 18

What is another name for historical?

Answer 18

Reterospcetive

Question 19

Why are cohort studies good?

Answer 19

Comparative study
Measures co founders
Can see the effects of a specific exposure

Question 20

What is internal comparison in cohort study?

Answer 20

When you subdivide the level of exposure to give relative risk.
Compare exposed and unexposed within cohort.

Question 21

What calculation is used in internal comparisons)

Answer 21

Incidence Rate Ratio

Question 22

Characteristics of internal comparisons?

Answer 22

Very different sized cohorts - small exposed means larger error factor
Large study required
Confounders

Question 23

What is an external comparison?

Answer 23

Compared those exposed to external reference population - eg the general public

Question 24

Calculation in external comparison?

Answer 24

Standardised Morbidity Rate

Question 25

Characteristics of external comparison?

Answer 25

Complicated to standardise as the expected # cases. The cohort study members increase age hence complicated to work out age-specific rates. Can study serious diseases using large cohorts Limited population data Healthy worker effect

Question 26

What is the healthy worker effect?

Answer 26

A selection bias. Study involves workers/employed to reference population. Workers tend to be healthier than unemployed hence can work. Any test involving exposure to something at work. Comparison, should always be against other working people to prevent bias

Question 27

What is used to calculate the expected #cases in external comparison of cohort studies?

Answer 27

Lexis diagram

Question 28

What is a lexis diagram?

Answer 28

Shows the age-sex rates observed for given age group and calendar period

Question 29

What are the age-sex rates in lexis diagram limited to?

Answer 29

Routine data source

Question 30

What does an arrow on a lexis diagram mean?

Answer 30

Period of follow-up for an individual in the cohort study

Question 31

What does each square of a lexis diagram represent?

Answer 31

The p-y of observation for a given age group& calendar period

Question 32

When are external comparisons good?

Answer 32

Good when able to use sub-cohorts as limited data

Question 33

Limitations of external comparisons?

Answer 33

When no incidence data Might only have mortality data No comparible ie HWE Limited data on reference pop

Question 34

How are cohort studies better that case-control?

Answer 34

Ranges of outcomes Can study rare exposures Exposure proceeds outcome

Question 35

Positives to cohort?

Answer 35

Detailed assessment of exposure, outcomes and co founders Better than case-control Better for conditions that fluctuate with age

Question 36

Negatives to cohort?

Answer 36

Time and resource intensive as large Risk of high loses to follow up hence survivor bias Not good for rare outcomes as too few cases Unknown cofounders can't be adjusted for

Question 37

What is non-responder bias?

Answer 37

The characteristic of non-responders may be different to those responding to surveys he be despite a larger sample, a low response rate does not necessarily result in more of a representative of the pop.

Question 38

What type of survey sample gives the most representative response?

Answer 38

Large sample size and large response rate

Question 39

When creating a survey you need to think about?

Answer 39

``` Definition of disease and the types Method of diagnosis Sampling frame Sampling proportion Sampling technique Response Interpretation of data ```

Question 40

Smaller the survey?

Answer 40

The higher the chance variation

Question 41

Out of median and means, which is less influenced by extreme values?

Answer 41

Median is less influenced

Question 42

Disadvantage to mode?

Answer 42

Misleading in skewed distribution

Question 43

Can routine and administrative data make errors?

Answer 43

Yes. | Either interpretation of data or coding error.