Unit 4 test stats

In a statistical study is the entire group of individuals we want information about.

Collects data from every individual in the population.

is a subset of individuals in the population which we actually collect data.

for studies that use an organized plan to choose a sample that represents some specific population.

is a sampling method that involves choosing individuals from the population who are easy to reach. It is generally biased because they don’t really represent the entire population.

is shown in a statistical study when it consistently underestimates or overestimates the value you want to know. Bias is the tendency for a sample to differ from the corresponding population in some systematic way. Some part of the population is systematically favored over another part.

Consists of people who choose themselves by responding to a general invitation. They are generally biased as they over represent people with strong opinions.

Involves using a chance process to determine which members of a population are included in the sample. Larger random samples typically give better information about the population than smaller samples.

of size n is chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample. An SRS also gives each member of the population an equal chance to be included in the sample.

is a table of random digits and can be used to choose individuals randomly.

starts by classifying the population into groups of similar individuals, called strata. Then choose a separate SRS in each stratum and combine these SRSs to form the sample.

starts by classifying the population into groups of individuals that are located near each other, called clusters. Then choose an SRS of the clusters. All individuals in the chosen clusters are included in the sample.

Is the process of drawing conclusions about a population on the basis of sample data.

Occurs when some members of the population cannot be chosen in a sample.

Occurs when an individual chosen for the sample cannot be contacted or refuses to participate.

Occurs when inaccurate answers are given in survey questions. Some reasons are wording of the question, appearance of the interviewer, asking about illegal behavior, unpopular beliefs, past events, taking measurements.

Observes individuals and measures variables of interest but does not attempt to influence the responses. Looking for patterns or associations. No cause or effect.

Deliberately imposes some treatment on individuals to measure their responses. Must give treatment. Used to figure out cause and effect.

Occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other. What is something else that is contributing to the response variable.

Is a specific condition applied to the individuals in an experiment, If an experiment has several explanatory variables, a treatment is a combination of specific values of these variables (also called factors).

Are the smallest collection of individuals to which treatments are applied. When the units are human beings, they often are called subjects. Who is being assigned.

In an experiment means that experimental units are assigned to treatments using a chance process. Doing so helps create roughly equivalent groups of experimental units by balancing the effects of other variables among the treatment groups.

Is the attempt to keep other variables that might affect the response the same for all groups. None of the treatment in this group.

Use enough experimental units in each group so that any differences in the effects of the treatments can be distinguished from chance differences between the groups. Repeat the experiment because there are enough subjects. “have enough experimental units”

Is using an experimental design that compares two or more treatments. Must at least two treatments.

Is used to provide a baseline for comparing the effects of the other treatments.

Has the experimental units assigned to the treatments completely by chance. Flow chart.

Result occurs when the observed effect of an experiment is so large that it would rarely occur by chance. Results are very different.

Neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received.

if one party knows and the other does not. one group is blind and the other isn’t.

Is the fake treatment given to control group in an experiment.

Occurs when some patients taking the placebo improve.

A block is a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments. In a randomized block design, the random assignment of experimental units to the treatments is carried out separately within each block. Block → split the group into blocks → becomes similar.

Is a common form of blocking for comparing just two treatments. In some matched pairs designs, each subject receives both treatments in a random order. In others, two very similar subjects are paired, and the two treatments are randomly assigned within each pair. Data collected in pairs.

1. Comparison

2. Random assignment

3. Control

4. Replication