Statistics Flashcards
PPV and NPV changes with prevalence
PPV will rise with higher prevalence
NPV will rise with lower prevalence
Positive and negative likelihood ratio equation
Positive: sens/ (1-spec)
Negative: (1-sens)/ spec
Clinical trials phases 0-4
Phase 0: prelim PK/PD info
Phase 1: healthy volunteers for safety and toxicity, PK, PD
Phase 2: larger to look at dose and efficacy
Phase 3: RCT for efficacy (cf good standard)
Phase 4: post marketing survellience for safety vigilance
Adoption vs twin studies
Adoption to look at genetic influences in same environment
Twin studies to review affects of genes (mono vs diz)
Cohort studies down side
Prone to loss to follow up
Pre registration of trials prevents?
Publication bias
Type 1 and 2 error
1 error concluding there is different when one doesn’t exist (p value) “false positive”
2 error concluding there is no difference when there is one (power) “false negative”
SD 1 standard deviation and 2 standard deviation (percentage)
1: 68% (16% above and 16% below)
2: 95%
3: 99.7%
What is variance?
SD squared
Intention to treat important why
Underestimated true effect
Maintains randomisation to overcome selection bias
Pre test odds take into account
Patient characteristics and prevalence
Multivariate analysis two groups
Multiple regression (continuous variable) Logistic regression (dichotomous)
Size of box on forest plot
Related to quality and size of study
Your region has a birth rate of about 50,000 babies per year. About 50 preschool children are diagnosed
each year with “crumblitis”, a rare gastrointestinal disorder, the cause of which is unknown. You hypothesise
that this condition is related to maternal ingestion of orange rhubarb during pregnancy.
Which one of the following is the most appropriate research design to test your hypothesis?
Case control
SIDS percent of deaths
7%