1. How to assess an abstract

2. Objectives
Understand the principle differences between qualitative and quantitative research
Understand the basic statistics employed in research
Be able to assess a piece a research with confidence!

3. Qualitative research Which type of questions does it answer?
What methodologies are employed?
Improving their validity

4. Assessing a qualitative paper
Is the qualitative approach appropriate?
Methodology
Data analysis
Results and conclusion

5. Quantitative Types of quantitative research
RCT – design features, advantages & disadvantages
Cohort Studies
Case control studies
Cross section surveys

6. BIAS Selection bias Observer bias Participant bias
Withdrawal or drop out bias
Recall bias
Measurement bias
Publication bias
Selection bias – select sicker patients to get the active or new Rx and fitter patients to get placebo or older Rx
Observer bias – if we know the patient has active treatment can subconsciously record health status as being better
Participant bias – e.g. in study looking at Gi bleeds in NSAID v non-NSAID users, the people who are not prescribed NSAIDs buy them OTC.
Withdrawal / drop out – if lose people from the study those left at thend may not be representative of those originally included, and their numbers may be very much smaller so affecting the validity and generalisability of event rates.
Recall – mothers of kids with leukaemia remember living near high voltage cables. Mothers of kids without leukaeimia won’t remember living near cables coz to them it’s a trivial fact.
Measurement bias – e.g. measuring BP in trials with sphygs that are not calibrated
Publication bias – positive studies get published much more often than equivocal or negative studies

7. Assessing quantitive research

8. Commonly used statistics
P values
Relative Risk Reduction
Absolute Risk Reduction
Numbers Need to Treat
Sensitivity
Specificity
Positive Predictive Value
Negative Predictive Value

9. P values & CI
p value = the probability of the outcome being due to chance
p = 1 in 20 (0.05).
> 1 in 20 (0.051) = not significant
< 1 in 20 (0.049) = statistically significant
CONFIDENCE INTERVALS
This defines the range of values between which we could be 95% certain that this result would lie if this intervention was applied to the general population
Straightforward, surely. If not see Simple Statistics by Frances Clegg, Cambridge Press.

10. RR, AR, ARR & RRR
What are they?
How do you calculate them?

11. Warfarin & AF study
The annual rate of stroke was 4.5% for the control group
Absolute Risk (Control group) = 0.045
1.4% for the warfarin group
Absolute Risk (experimental group) = 0.014
Absolute Risk Reduction = – = 0.031
NNT = 32
Relative Risk = 0.014/0.045 = 0.31 = 31%
Relative Risk Reduction = – 0.014/0.045 = 0.68 = 68%

12. 1/ARR = Number Needed to Treat.
NNT
How many people you need to treat with the study intervention to stop the study event from happening once.
1/ARR = Number Needed to Treat.

13. NNT EXAMPLES
But these are all in different patient groups with interventions with very different costs so tables of NNTS are illustrative but no answer.

14. Screening tests – assessing their performance

15. Sensitivity
The test’s ability to correctly identify those people with disease.
If Sensitivity is <100% Disease is missed.
So = True Positives
True Positives + False negatives
i.e. all those who truly Have the disease

16. Specificity
The test’s ability to correctly exclude those people without disease
If Specificity <100% then healthy people are told they may have disease
= True Negatives
True Negatives + False Positives
i.e. all those who truly don’t have the disease

17. Positive predictive value
If the test is positive, what is the chance of the person having the disease = positive predictive value.
True Positives
True positives + False Positives

18. Negative Predictive Value
If the test is negative, what chance is there that the person doesn’t have the disease = negative predictive value.
True negative
True negative + False negative

19. Accuracy True positive + True negative
True negative +true positive+ false negative + false positive

20. Urine dipstick to screen for Diabetes
Example- urine dip test vs GTT (the gold standard)
Diabetes +ve Diabetes –ve
Result of urine test (n=27) (n=973)
Glucose present (13) True +ve 6 False +ve 7
Glucose absent (987) False –ve 21 True -ve 966