Intro to statistics

Population

The entire collection of items from which samples can be drawn.

Sample

Items selected at random from a population and used to test hypotheses about the population.

Experiment

The act of conducting a controlled test or investigation.

Observational Study

An experiment which observes individuals and measures variables of interest but does not attempt to influence the responses.

Variability

Can change uniformity of a data set.

Natural Variability

Variability that accounts for the fact that members of a population are simply different.

Induced Variability

Variability because we have assigned our population or sample to two or more treatment groups and then observe the variability between the groups.

Sample Variability

Variability that occurs when we take multiple samples from a population randomly.

Systematic Sampling

A method of sampling where individuals are selected at regular intervals from a sorted list.

Surveys

Collections of data from a population.

Sampling Variability

Variability due to the sample itself.

Bias in Sampling

Occurs when a sample is not representative of the population as a whole.

Controlled Test

An investigation where one or more variables are manipulated to observe the effect on another variable.

Response Variable

The variable that is measured in an experiment.

Independent Measurement

How two different people read the measurement.

Reaction Time

The time it takes for a person to respond to a stimulus.

Memory Test

An experiment where one group is allowed to sleep for 8 hours and another for 4 hours to observe differences in memory.

Political Candidate Preference

Determined by surveying multiple samples of people.

Marketing Sample

A random sample taken by a marketing company to see which major soda is preferred in the general population.

Natural Grocery Store Bias

Sampling people in a natural grocery store may introduce bias because they do not represent the population as a whole.

Data Collection

The process of gathering information from a population.

Probability Sampling Method

A type of probability sampling method in which sample members from a larger population are selected according to a random starting point but with a fixed, periodic interval.

Self-selection Bias

The problem that can result when survey respondents are allowed to decide entirely for themselves whether or not they want to participate in a survey.

Survivorship Bias

A bias that occurs when only the sample that passes the selection criteria is considered, ignoring those that failed to pass.

Randomization

The process of assigning individuals (or items) randomly to treatment groups in order to determine the effect of the treatment on the variability of the data.

Experimental Study

A study where individuals are assigned randomly to treatment groups, and the assignment is under the control of those performing the study.

Example of Self-selection Bias

In a mail-in poll about reading ability, only those who received and read the survey would likely respond, skewing results.

Example of Survivorship Bias

Studying business performances in an industry without considering failed organizations may lead to misleading positive results.

Random Assignment Importance

Random assignment is crucial to ensure that differences in outcomes are due to treatment and not pre-existing differences.

Fixed Periodic Interval

A method in sampling where after selecting a starting point, every nth member is chosen until the end of the list is reached.

Looping in Sampling

When the end of the list is reached in sampling, the count loops back to the beginning to finish the selection process.

Example of Random Assignment

Seeds divided into two groups, one receiving organic fertilizer and the other synthetic, to study growth rates.

Measurement Variability

Variability that can occur in measurements due to natural differences among subjects or items being studied.

Bias in Study Results

Results may not accurately represent the whole population if biases like self-selection or survivorship are present.

Treatment Group Assignment

The process of assigning individuals to different groups in a study to test the effects of various treatments.

Data Collection Method

The approach used to gather information from participants in a study, which can influence the validity of results.

Control in Experiments

The ability of researchers to manage how subjects are assigned to treatment groups, ensuring randomization.

Example of a Study

Exploring the relationship between a person's state of residency and their income level through random sampling.

Impact of Bias on Conclusions

Bias can lead to incorrect conclusions if the sample does not accurately represent the population being studied.

Types of Bias

Various forms of bias that can affect the validity of research findings, including self-selection and survivorship bias.