RCT
- therapeutic à trial for laser eye surgery
- intervention à pap smears to detect early signs of cervical cancer
- preventative à oestrogen treatment to prevent osteoporosis
- double blinding à observer
- what is triple blinding
| Aetiological factor | Risk factor | Disaese |
| low dietary calcium | no dairy products in diet | osteoporosis |
| salmonella | unhygienic food preparation | food poisoning |
| carcinogens in smoke | cigarette smoke | lung cancer |
No statistically significant relationship
- no relationship exists
- there is a relationship, but trial unable to detect (eg, low power)
Strategy to assess subject compliance
- testing of blood etc
Keeping subjects enrolled
- incentive or inducement
- altruism
- promise if assigned to control group, that they will be offered treatment after trial
Baseline characteristics of study groups differ
- realloc subjects randomly to groups after stratifying on key variables
- randomly discard subjects with certain characteristics
- include variables with imbalance as covariates
Withdrawal of subjects in trial
- decrease power
- increase likelihood of type 2 error
Randomization
- only then can outcome between groups be ascribed to treatment
- if randomization omitted à differences in outcome may be due to differing characteristics of groups
- unbiased distribution of risk factors
Incidence / Prevalence
- incidence à rate of appearance of new cases
- prevalence à proportion of cases in population
Duration = Prevalence / Incidence
Chi Square degrees of freedom
- (c – 1 ) ( r – 1 )
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