PubHealth Biostatistics and Experimental Design

No observed effect level - NOEL

highest dose of a substance, or exposure to an agent that does NOT produce an observable effect

Allowable daily intake - ADI

amount of chemical to which humans can be exposed on a daily basis over an extended period of time, without suffering a deleterious effect

ADI formula

(NOEL) / (safety factor)

• safety factor is typically 100

LD50

dose of a substance that causes death in 50% of the population

• mg of substance/kg of body weight

LD50 measures __.

acute toxicity

Feature of a clinical trial designed to determine efficacy of a new drug

• randomisation

• control group or placebo

• adequate sample sizing

• binding

• standardised protocol and follow up

Randomisation

participants randomly assigned to control or treatment group

Adequate sample size is required to detect __.

statistically significant differences

Binding can be…

single or double

Single binding

subjects unaware of whether they’re receiving treatment or placebo

Double binding

subjects nor investigators know who is receiving treatment or placebo

The null hypothesis states that there is…

NO difference between the sample groups

• result analysis aims to either reject or accept it

The p-value is the probability of…

finding the observed results if the null hypothesis is true

If the p-value is above the critical value, then…

the null hypothesis is accepted

• no significant difference between groups

If the p-value is below the critica value, then…

the null hypothesis is rejected

• significant difference between groups

The p-value indicates how strong the evidence is…

against the null hypothesis

Type I error

null hypothesis is incorrectly rejected despite it being true

Type II error

null hypothesis is incorrectly accepted despite it being false

Bias control methods

• randomised trials

• binding

• placebo use

• active participation and cooperation

these are all features of a clinical trial designed to determine efficacy of a new drug

Non-compliance __ ability of investigators to detect a difference between groups.

reduces

Frequent contact with subjects and incentives to continue are required to…

enhance compliance throughout the study

The correlation coefficient, r. studies the…

degree of relationship between two variables

• ranges from -1 to 1

r = -1

perfect negative relationship

• as value of one variable increases, the other variable’s value decreases

r = 0

no liner relationship between the two variables

• does NOT mean the variables are unrelated

r = 1

perfect positive linear relationship between the two variables

• both variables increase or decrease with each other

r measures how close to a __ the data lies.

straight line

Confounding

association between one factor and a disease outcome is false and explained by another factor

• negative health attitudes lead to smoking and poor oral hygiene which can lead to periodontal disease

Confounding can…

• create the appearance of a relationship when one does NOT exist

• mask a relationship that DOES exist

• modify the strength of a relationship