Skew the results of a study in a certain direction
Is an experimental technique in which individuals involved in the study are kept unaware of treatment assignments
A survey that attempts to collect all information on the population
Randomly select large units consisting of smallest sub units
The general objective of comparative studies is to learn about the relationship but explanatory and response variables.
Is a distortion in an association between an explanatory variable and brought about by the influence of extraneous factors.
Trials with one or more control groups
The study subjects and the investigators making measurements are kept in the dark about the treatments
Doubt about beliefs and risk must be in perfect balance before the trial begins.
The investigator assigns the exposure to one group while learning the other non exposed
The explanatory variable is the treatment or exposure that explains or predicts changes in the response value.
Explanatory variables in experiments will be referred to as factors.
When two factors produce an effect that would otherwise not be predicted by studying them separately.
Are variables lurking within study subjects
Techniques in which large scale units are selected at random.
Non experimental studies
The investigator merely classifies individuals are exposed or non exposed without intervention. Also called observations studies.
Occurs when a large percentage of individuals refuse to participate in a survey or cant be contacted. Non res ponders often differ systematically from res ponders skewing results of surveys.
Various types of control groups may be used in experimental studies. A placebo is an inert substance.
A particular section or group of people living in a certain area
Is a sample in which each member of the population has a known probability.
Randomized Control Trial
When the assignment of the treatment is based on chance.
A portion of the population
the individuals or clusters of individuals who might actually be selected for inclusion in the sample
Each population member has the probability of being selected into a sample or the likelihood of not selecting another
The sample must contain an element of chance a random must be used. The most fundamental type of random sample.
The subjects are kept in the dark about the specific type of treatment they are receiving.
Stratified Random sample
Is a sample in which each member of the population has a known probability of being selected into the sample.
Refers to a person who participates in a study
Used to quantify population characteristics.
Is a specific set of factors applied to subjects
Experiments involving human subjects
The study subjects investigators and those doing stats don't know treatment plans
Occurs when some groups in the sample population are left out or are underrepresented on the population listing. Sampling from such a list will undermine the goal of achieving equal probability of a selection.
Can occur because self selected participants of a survey ten to be atypical of the population. For example web surveys are usually skewed because participants have an interested for something the website offers.