STATISTICS - EXPERIMENT DESIGN
Convenience Sample: A sample of individuals easily accessible to the researcher. This method is quick but often leads to bias as it may not accurately represent the entire population.
Systematic Random Sample: A sample created by selecting every kth individual from an ordered list of the population. The starting point is chosen randomly.
Question of Interest: The specific question a researcher is trying to answer.
Statistic: A numerical value that describes a sample, like the average height of students in a randomly selected class.
Nonresponse: Occurs when an individual selected for a survey doesn't participate, which can introduce bias if those who don't respond differ from those who do.
Simple Random Sample: A method where every individual and every group of individuals in a population has an equal chance of being selected for the sample. This is the gold standard for unbiased sampling.
Multistage Random Sample: A sampling technique that involves multiple stages of random selection. For example, first randomly selecting states, then randomly selecting cities within those states, and finally randomly selecting households within those cities.
Geographic Limitation: A bias that occurs when a study is limited to a specific geographic area, making its findings difficult to generalize to other regions.
Census: A survey that attempts to collect data from every single member of a population.
Wording Effects: The influence of how questions are phrased, which can introduce bias by leading a person toward a particular answer.
Cluster Random Sample: A sampling method where the population is divided into groups (clusters), and a random sample of these clusters is chosen. All individuals within the selected clusters are then surveyed.
Parameter: A numerical value that describes an entire population, which is typically unknown. For example, the true average height of all students in a school.
Undercoverage: A bias that happens when some members of the population are not included in the sampling frame and thus have no chance of being selected.
Response Bias: The tendency of a person to give an inaccurate or untruthful answer, possibly due to social pressure or the desire to please the interviewer.
Stratified Random Sample: A sampling method where the population is divided into homogeneous subgroups (strata), and a simple random sample is taken from each stratum to ensure representation from all groups.
Bias: A systematic error in a study that results in an over- or underestimation of the true population parameter.
Population: The entire group of individuals that a researcher is interested in studying.
Voluntary Response Sample: A sample made up of individuals who choose to participate in a survey. This often leads to strong bias because people with strong opinions are more likely to respond.
Statistical Inference: The process of using data from a sample to draw conclusions about a larger population.
Experimental Designs
Experiment: A study where the researcher deliberately applies a treatment to a group of subjects to observe the effect.
Factors: The independent variables that are manipulated by the researcher. For example, in a study on plant growth, the type of fertilizer and the amount of water could be factors.
Double Blind Test: An experiment where neither the subjects nor the researchers know who is receiving the treatment and who is in the control group. This prevents bias from both sides.
Statistically Significant: A result that is unlikely to have occurred by random chance.
Multiple Analysis: The practice of analyzing data in several different ways to ensure the findings are robust and not a result of a specific statistical method.
Control Group: The group that does not receive the treatment or receives a placebo. It serves as a baseline for comparison.
Replication: The process of repeating an experiment with different groups of subjects to confirm the original findings and ensure they were not due to chance.
Observational Study: A study where researchers observe and measure variables without attempting to influence the outcomes. This type of study can show correlation but not causation.
Lack of Realism: A limitation that occurs when the experimental setting is so artificial that the results can't be generalized to real-world situations.
Blind Test: An experimental procedure where the subjects do not know if they are receiving the treatment or a placebo. This helps to prevent the placebo effect.
Random Assignment: The process of assigning subjects to different experimental groups (treatment and control) by chance. This helps to create equivalent groups and reduces the impact of confounding variables.
Confounding Variables: Extraneous variables that influence both the independent and dependent variables, potentially creating a false association between them.
Treatment: The specific experimental condition applied to the subjects.
Media Bias: The tendency for news outlets to slant their reporting, which can influence public perception of a study's results.
Placebo: An inactive substance or treatment given to the control group to mimic the treatment and account for the psychological effects of receiving a treatment.
Anecdotal Evidence: Evidence based on personal accounts or stories, which is often unreliable and can't be used to make broad conclusions.
Response Variable: The dependent variable that is measured to see if it's affected by the treatment.
Psychological Effects: Changes in a person's health or behavior that are caused by their beliefs or expectations about a treatment.
Control: The overall effort to keep all conditions in an experiment constant except for the treatment.
Subjects: The individuals or units on whom the experiment is conducted.