# Critical appraisal / QIP Flashcards

What is absolute risk reduction?

Measure of effect

Incidence of outcome in experimental group minus the incidence of outcome in the control group

= CER - EER

Of 100 patients in the treatment group, 20 died. 30 of 100 died in the placebo group. What is the absolute risk reduction?

30/100 (0.3) - 20/100 (0.2) = 10/100 or 0.1 or 10%

What is bias?

Systematic difference in the way a study is conducted that leads to less valid results

What is bias ascertainment?

Bias when measurements are performed differently

What is bias expectation?

Bias when those collecting data are influenced by their own knowledge

What is bias follow up?

When loss to follow up differs between two groups

What is bias inclusion?

When subjects included in groups are not at random

What is a confidence interval?

Confidence an estimated effect is between two values - 95% normally chosen confidence interval

What value makes a confidence interval statistically significant?

<1

What is a confounding variable?

Variable associated with both the exposure and outcome of interest which can lead to inappropriate conclusions re: association

What is effectiveness?

How well an intervention works in the real world

What is efficacy

How well an intervention works under ideal conditions

What is heterogenecity?

The amount of variation of results of trials included in systematic reviews. Less heterogenecity increases likelihood of results being true

Describe intention to treat analysis

Patients analysed by which group they end up in, not where they were allocated.

I.e if patients stopped take the treatment for whatever reason, they are still analysed in the intervention arm. This increases chance of type 2 error (i.e. less likely to show a difference) but takes into account what happens in real life.

What is JADAD score?

Rank of methodological quality (0-5)

What is kappa?

Concordance between observers.

1 = perfect agreement

0 = absolute disagreement

What is a negative likelihood ratio?

how likely is a negative test to be found in a person without the disease than in a person with the disease?

How good a test is at excluding a disease

How is a negative likelihood ratio calculated?

(1 - sensitivity) / specificity

i.e. false negative / true negative

What values of a negative likelihood ratio show a useful test?

Number will be <1.0

<0.2 useful

<0.1 very useful

What is a positive likelihood ratio?

How much more likely is a positive test to be found in a person with the disease than in someone without the disease

ie. How good is a test at ruling in a disease

How is positive likelihood ratio calculated?

(sensitivity / (1- specificity)

i.e. true positive/ false positive

What positive likelihood ratios values show usefullness?

Value will be >1.0

5-10 useful

> 10 very useful

What is sensitivity?

How many true positives does a test pick up as a proportion of all positives

How is sensitivity calculated?

A/ A + C

What is specificity?

How many true negatives dose a test pick up, as a proportion of all negatives?

How is specificity calculated?

D / B + D

What is negative predictive value?

If a patient has a negative test, how likely are they not to have the disease?

How is a negative predictive value calculated?

D/ C + D

How is positive predictive value calculated?

A / A + B

What is positive predictive value?

If a patient has a positive test what is the probability of them having the disease?