#### Prospective Versus Retrospective

Prospective vs. Retrospective A prospective study is one that identifies a scientific (usually medical) problem to be studied, specifies a study design protocol (e.g. what you're measuring, who you're measuring, how many subjects, etc.), and then gathers data in the future in accordance with the…

#### Disproportionate Stratified Random Sampling

Disproportionate stratified random sampling: See Stratified Sampling (method ii). Browse Other Glossary Entries

#### Sample Size Calculations

Sample Size Calculations: Sample size calculations typically arise in significance testing, in the following context: how big a sample size do I need to identify a significant difference of a certain size? The analyst must specify three things: 1) How big a difference is being…

#### Effect

Effect: In design of experiments, the effect of a factor is an additive term of the model, reflecting the contribution of the factor to the response. See Variables (in design of experiments) for an explanatory example. Browse Other Glossary Entries

#### Self-Controlled Design

Statistical Glossary Self-Controlled Design: In randomized trials, a self-controlled design is one in which results are measured in each subject before and after treatment. Both parallel designs and crossover designs can also include a self-controlled feature. Browse Other Glossary Entries

#### Effect Size

Effect Size: In a study or experiment with two groups (usually control and treatment), the investigator typically has in mind the magnitude of the difference between the two groups that he or she wants to be able to detect in a hypothesis test. This magnitude,…

#### Sequential Analysis

Sequential Analysis: In sequential analysis, decisions about sample size and the type of data to be collected are made and modified as the study proceeds, incorporating information learned at earlier stages. One major application of sequential analysis is in clinical trials in medicine, where successful…

#### Error Spending Function

Error Spending Function: See alpha spending function. Browse Other Glossary Entries

#### Stratified Sampling

Stratified Sampling: Stratified sampling is a method of random sampling. In stratified sampling, the population is first divided into homogeneous groups, also called strata. Then, elements from each stratum are selected at random according to one of the two ways: (i) the number of elements…

#### Interim Monitoring

Interim Monitoring: In clinical trials of medical treatments or devices, a traditional fixed sample design establishes a fixed number of subjects or outcomes that must be observed. In a trial that uses interim monitoring, the sample size is not fixed in advance. Rather, periodic looks…

#### Systematic Sampling

Systematic Sampling: Systematic sampling is a method of random sampling. The elements to be sampled are selected at a uniform interval that is measured in time, order, or space. Browse Other Glossary Entries

#### Lan-Demets Spending Function

Lan-Demets Spending Function: See alpha spending function. Browse Other Glossary Entries

#### Time-series data

Time-series data: See longitudinal data Browse Other Glossary Entries

#### Latin Square

Latin Square: The Latin Square is a square array in which every letter or symbol appears exactly one in each row and in each column. B C D A C D A B D A B C A B C D Browse Other Glossary Entries

#### Longitudinal Analysis

Longitudinal Analysis: Longitudinal analysis is concerned with statistical inference from longitudinal data Browse Other Glossary Entries

#### Alpha Spending Function

Alpha Spending Function: In the interim monitoring of clinical trials, multiple looks are taken at the accruing results. In such circumstances, akin to multiple testing, the alpha-value at each look must be adjusted in order to preserve the overall Type-1 Error. Alpha spending functions, (the…

#### Longitudinal Data

Longitudinal Data: Longitudinal data refer to observations of given units made over time. A simple example of longitudinal data is the gross annual income of, say, 1000 households from New York City for the years 1991-2000. See also: cross-sectional data , panel data , Cohort…

#### Attribute

Attribute: In data analysis or data mining, an attribute is a characteristic or feature that is measured for each observation (record) and can vary from one observation to another. It might measured in continuous values (e.g. time spent on a web site), or in categorical…

#### Longitudinal study

Longitudinal study: Longitudinal studies are those that record data for subjects or variables over time. If a longitudinal study uses the same subjects at each point where data are recorded, it is a panel study . If a longitudinal study samples from the same group…

#### Categorical Data

Categorical Data: Categorical data are reflecting the classification of objects into different categories. For example, people who receive a mail order offer might be classified as "no response," "purchase and pay," "purchase but return the product," and "purchase and neither pay nor return." Browse Other…

#### Paired Replicates Data

Statistical Glossary Paired Replicates Data: Paired replicates is the simplest form of repeated measures data , when only two measurements are made for each experimental unit. Consider, for example, a study of 2 drugs - A and B - to determine whether they reduce arterial…

#### Cohort study

Cohort study: A cohort study is a longitudinal study that identifies a group of subjects sharing some attributes (a "cohort") then takes measurements on the subjects at various points in time and records data for the group. A cohort study is often used to compare…

#### Panel Data

Panel Data: A panel data set contains observations on a number of units (e.g. subjects, objects) belonging to different clusters (panels) over time. A simple example of panel data is the values of the gross annual income for each of 1000 households in New York…

#### Cross sectional study

Cross sectional study: Cross sectional studies are those that record data from a sample of subjects at a given point in time. See also cross sectional data , longitudinal study . Browse Other Glossary Entries

#### Panel study

Panel study: A panel study is a longitudinal study that selects a group of subjects then records data for each member of the group at various points in time. See also panel data . Browse Other Glossary Entries

#### Cross-sectional Analysis

Cross-sectional Analysis: Cross-sectional analysis is concerned with statistical inference from cross-sectional data . Browse Other Glossary Entries

#### Parallel Design

Parallel Design: In randomized trials, a parallel design is one in which subjects are randomly assigned to treatments, which then proceed in parallel with each group. Conducted properly, they provide assurance that any difference between treatments is in fact due to treatment effects (or random…

#### Cross-sectional Data

Cross-sectional Data: Cross-sectional data refer to observations of many different individuals (subjects, objects) at a given time, each observation belonging to a different individual. A simple example of cross-sectional data is the gross annual income for each of 1000 randomly chosen households in New York…

#### Repeated Measures Data

Repeated Measures Data: Repeated measures (or repeated measurements) data are usually obtained from multiple measurements of a response variable. Such multiple measurements are carried out for each experimental unit over time (as in a longitudinal study ) or under multiple conditions. An essential statistical peculiarity…

#### Crossover Design

Crossover Design: In randomized trials, a crossover design is one in which each subject receives each treatment, in succession. For example, subject 1 first receives treatment A, then treatment B, then treatment C. Subject 2 might receive treatment B, then treatment A, then treatment C.…

#### Response

Response: In design of experiments, response is a dependent variable. Its values are measured for all subjects, and the question of primary interest is how factors affect the response. See Variables (in design of experiments) for an explanatory example. Browse Other Glossary Entries