Why is random assignment used to assign people to treatment groups and control groups in a controlled experiment?
To make the groups as similar as possible, minimizing bias
. Which of the following is NOT one of the criteria for the “gold standard” for experiments?
Which of the following methods only allows us to conclude that there is an association between the treatment variable and the outcome variable?
An observational study
can conclude only that there is an association between the treatment variable and the outcome variable.
Which of the following is a reason we can never draw cause and effect conclusions from observational studies?
note: You can never draw cause-and-effect conclusions from observational studies because of
potential confounding variables
. An observational study can conclude only that there is an association between the treatement variable and the outcome variable.
Why can’t we draw conclusions about the relationship between variables in an observational study?
Observational studies can never identify causal relationships
because even though two variables are related both might be caused by a third, unseen, variable. Since the underlying laws of nature are assumed to be causal laws, observational findings are generally regarded as less compelling than experimental findings.
Contingency tables (also called crosstabs or two-way tables)
are used in statistics to summarize the relationship between several categorical variables. A contingency table is a special type of frequency distribution table, where two variables are shown simultaneously.
Why is random assignment important in an experiment?
Random assignment helps
ensure that members of each group in the experiment are the same
, which means that the groups are also likely more representative of what is present in the larger population.
What is another name for a regression line quizlet?
Another name for the regression line is
the least squares line
because it is chosen so that the sum of the squares of the differences between the observed y-value and the value predicted by the line is as small as possible.
What must happen in a study to determine cause and effect?
One of the main strengths of
experimental research
is that it can often determine a cause and effect relationship between two variables. By systematically manipulating and isolating the independent variable, the researcher can determine with confidence the independent variable’s causal effect on the dependent variable.
What is a covariate example?
For example, you are
running an experiment to see how corn plants tolerate drought
. Level of drought is the actual “treatment”, but it isn’t the only factor that affects how plants perform: size is a known factor that affects tolerance levels, so you would run plant size as a covariate.
What are two basic types of variables in statistics?
Discrete and continuous variables
are two types of quantitative variables: Discrete variables represent counts (e.g. the number of objects in a collection). Continuous variables represent measurable amounts (e.g. water volume or weight).
How do you tell if a study is observational or experimental?
- In an observational study, we measure or survey members of a sample without trying to affect them.
- In a controlled experiment, we assign people or things to groups and apply some treatment to one of the groups, while the other group does not receive the treatment.
What is a designed experiment in statistics?
A designed experiment is
a series of runs, or tests
, in which you purposefully make changes to input variables at the same time and observe the responses. In industry, designed experiments can be used to systematically investigate the process or product variables that affect product quality.
What is the advantage of an experiment over an observational study?
The main advantage of experiments over observational studies is that:
a well-designed experiment can give good evidence that the treatment actually causes the response
. an experiment can compare two or more groups. an experiment is always cheaper.
“A two-way table”
is used to summarize two potentially related categorical variables.
What is a variable in stats?
What is a variable? A variable is
any characteristics, number, or quantity that can be measured or counted
. A variable may also be called a data item. Age, sex, business income and expenses, country of birth, capital expenditure, class grades, eye colour and vehicle type are examples of variables.
Are eye colors categorical?
Gender and eye color are
examples of categorical variables
, because they place each individual into a category, such as people with blue eyes. Categorical variables can be summarized to show how often each category occurs. Another type of variable is a numerical variable.
