Biostatistics Terms

Question	Answer
alpha (α)	Probability of a Type I Error, rejecting a true null hypothesis
type I error	concluding a difference exists when it does not
alternative hypothesis	a refutable hypothesis arrived at from observation
Analysis of Covariance (ANOVA)	Linear model which controls for additional interaction effects
Analysis of Variance (ANOVA)	A linear model which allows for separating the impact of multiple effects. Image: Image1 (image/jpeg)
Bayesian Theorem	A procedure for revising and updating the probability of some event in the light of new evidence. Image: Bayes1 (image/gif)
beta (β)	The probability of a type II error, the error of failing to reject a false null hypothesis
Type II Error	Declaring that a difference does not exist when in fact it does.
Bias	Deviations of results or inferences from the truth, or processes leading to such deviation
Unbiased	A result or inference which does not deviate from the true value
binary variable (binary observation)	Observations which occur in one of two possible states
binomial distribution	The distribution of the number of ‘successes', X, in a series of n- independent Bernoulli trials where the probability of success at each trial is p and the probability of failure is q = 1- p .
Binomial mean	np where n is the number of trials and p is the probability of success on each trial
variance	npq=np(1-p) where n is the number of trials, p is the probability of success on each trial and q is the probability of failure on each trial
binomial skewness	( q - p )/( npq ) ^1/2 where n is the number of trials, p is the probability of success on each trial and q is the probability of failure on each trial
binomial kurtosis	ε-6/n+1/npq
Biostatistics	A branch of science which applies statistical methods to biological problems. The science of biostatistics encompasses the design of biological experiments, especially in medicine and health sciences.
bivariate	outcomes belong to two categories, e.g. yes/no, acceptable/defective “bivariate binomial distribution”
blinded study (blinding)	A procedure used in clinical trials to avoid possible bias by withholding which treatment is being applied.
Bonferroni correction	A procedure for guarding against a type I error when performing multiple significance tests. To maintain the probability of a type I error at some selected value (α), each of the m tests to be performed is judged against a significance level (α/m ).
case-control study	The observational epidemiologic study of persons with the disease (or other outcome variable) of interest and a suitable control (comparison, reference) group of persons without the disease.
categorical data	Categorical data represent types of data which may be divided into groups. Examples of categorical variables are race, sex, age group, and educational level.
censored observation	Such observations arise most frequently in studies where the main purpose variable is time until a particular event occurs (for example, time to death) when at the completion of the study, the event of interest has not happened to a number of subjects.
Central Limit Theorem	If the sample size is large enough, the distribution of sample means can be approximated by a normal distribution, even if the original population is not normally distributed.
Chi-Square Distribution	The sample statistic X2= ( n – 1) s2/σ2. The chi-square distribution is skewed, the values can be zero or positive but not negative, and it is different for each number of degrees of freedom.
Chi-square statistic	A statistic having, at least approximately, a chi-squared distribution.
Chi-square test for trend	A test applied to a two-dimensional contingency table in which one variable has two categories and the other has k ordered categories, to assess whether there is a difference in the trend of the proportions in the two groups.
clinical trial	test regimen to evaluate efficacy and safety
Phase I trial	Safety and pharmacologic profiles. The first introduction of a candidate vaccine or a drug into a human population to determine its safety and mode of action. In drug trials, this phase may include studies of dose and route of administration. usually fewer than 100 healthy volunteers.
Phase II trial	Pilot efficacy studies. Initial trial to examine efficacy usually in 200 to 500 volunteers; with vaccines, the focus is on immunogenicity, and with drugs, on demonstration of safety and efficacy in comparison to other existing regimens. Subjects are usually randomly allocated to study or control groups.
Phase III trial	Extensive clinical trial. This phase is intended for complete assessment of safety and efficacy. It involves larger numbers, perhaps thousands, of volunteers, usually with random allocation to study and control groups, and may be a multicenter trial.
Phase IV trial	This phase is conducted after the FDA has approved the drug for distribution or marketing. May include research designed to explore a specific pharmacologic effect, to establish the incident of adverse reactions, or to determine the effects of long-term use. Ethical review is required for phase IV clinical trials, but not for routine post marketing surveillance.
coefficient of variation (CV)	he measure of spread for a set of data defined as 100 x standard deviation / mean CV = s/x bar(100) = sample CV = σ/µ(100) = population
cohort study	(Syn: concurrent, follow-up, incidence, longitudinal, prospective study) study following-up on a cohort to determine outcomes and infer a causal relationship between the initial characteristics of the cohort and the outcome.
cohort	Subsets of a defined population can be identified who are, have been, or in the future may be exposed or not exposed, or exposed in different degrees, to a factor or factors hypothesized to influence the probability of occurrence of a given disease or other outcome.
complementary event	Mutually exclusive events A and B for which Pr(A) + Pr(B) = 1 where Pr denotes probability.
conditional probability	The probability that an event occurs given the outcome of some other event. Usually written, Pr(A l B).
confidence interval (CI)	A 95% confidence interval, for example, implies that were the estimation process repeated again and again, then 95% of the calculated intervals would be expected to contain the true parameter value.
confounding variable	an extraneous variable in a statistical model that correlates (positively or negatively) with both the dependent variable and the independent variable
contingency table (or two-way frequency table)	The table arising when observations on a number of categorical variables are cross-classified. Entries in each cell are the number of individuals with the corresponding combination of variable values.
continuous data	result from infinitely many possible values that correspond to some continuous scale that covers a range of values without gaps, interruptions or jumps, e.g. blood pressure.
controlled trial	A Phase III clinical trial in which an experimental treatment is compared with a control treatment, the latter being either the current standard treatment or a placebo.
correlation coefficient r (Pearson product moment)	Measure of relationship between two normally distributed variables Image: Stat 10 Eq 1 (image/gif)
covariate	explanatory variables, more specifically variables that are not of primary interest in an investigation, but are measured because it is believed that they are likely to affect the response variable
cox regression model (Proportional Hazards Model)	statistical model for survival analysis developed asserting that the effect of study factors on the hazard rate in the study population is multiplicative and does not change over time
critical value	The value with which a statistic calculated from sample data is compared in order to decide whether a null hypothesis should be rejected. The value is related to the particular significance level chosen.
crossover rate	The proportion of patients in a clinical trial transferring from the treatment decided by an initial random allocation to an alternative one.
cross-sectional study	(Syn: disease frequency survey, prevalence study) A study that examines the relationship between diseases (or other health-related characteristics) and other variables of interest as they exist in defined population at one particular time.
cumulative frequency distribution	The tabulation of a sample of observations in terms of numbers falling below particular values. The empirical equivalent of the cumulative probability distribution. An example of such a tabulation is shown.
degrees of freedom	Number of independent units of information in a sample relevant to the estimation of a parameter or calculation of a statistic.
dependent variable (response or outcome variable)	The variable of primary importance in investigations since the major objective is usually to study the effects of treatment and/or other explanatory variables on this variable and to provide suitable models for the relationship between it and the explanatory variables.
descriptive statistics	methods of summarizing and tabulating data that make their main features more transparent.
dichotomous observation	A nominal measure with two outcomes (examples are gender male or female; survival yes or no); also called binary
dichotomous scale	one that arranges items into either of two mutually exclusive categories, e.g. yes/no, alive/dead
discrete data	result when the number of possible values is either a finite number or a “countable” number
Discrete variable	a countable and finite variable
distribution (population)	In statistics this term is used for any finite or infinite collection of ‘units'

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	Created by Victor Moxley almost 6 years ago