*bias*if it systematically produces results that misrepresent a population

- For example, recording "happiness levels" on a sunny Saturday afternoon versus on a Monday morning.

categorical variable - responses that are not quantitative.

- For example, classroom numbers, while numerical themselves, cannot be meaningfully compared or operated on. It would not make any sense, whatsoever, to find the average classroom number in the building. Favorite color is another example of a categorical variable.
- "What is the most popular type of pet owned by students at your school?"

control group - in an experiment, this is the group that

*does not*receive the treatment; their untested results are compared to the experimental group for analysis.

Empirical Rule - In a normal distribution, the approximate percentage of data values that falls in any interval of the range of the data can be determined using just the mean and standard deviation.

- About 68% of all values fall within 1 standard deviation of the mean.
- About 95% of all values fall within 2 standard deviations of the mean.
- About 99.7% of all values fall within 3 standard deviations of the mean.

experiment - involves applying a treatment to some group or groups and measuring eh affects of the treatments

experimental group - in an experiment, this is the group that receives the treatment; their tested results are compared to the control group's untested results for analysis.

margin of error - the MOE is used to find a range of reasonable values used to estimate the population parameter based on a sample statistic

normal distribution - a distribution that can be modeled by a particular bell-shaped curve that is symmetric around the mean; also known as a normal curve.

observational study - you measure or observe members of a sample in such a way that they are not affected by the study

parameter - a piece of information about a variable that is based on the entire population, or group of people or things that is being studied.

percentile - the percentage of values less than or equal to a particular data value that is equal to the percentage of the total area under the distribution curve for that population to the left of that data value.

population - the entire set of all members of a group studied by a statistical question.

quantitative variable - numerical values that can be meaningfully compared, added, subtracted, or otherwise operated upon.

- For example, median weight of backpacks makes sense but average classroom number does not. Therefore, weight would be considered a quantitative variable, and classroom number would not.
- "What is the average number of pets owned by the students at school?"

sample - a subset of the population that is being studied to answer a statistical question about the population.

sample survey - asks every member of a sample the same set of questions and records the answers

sampling distribution - the distribution of sample statistics, such as means or proportions from different sample of the same population.

simple random sample - each member of the population is equally likely to be chosen, and each possible sample of of the size you want is equally likely to be chosen.

skewed distribution - a distribution with a shape that is stretch out in either the positive or negative direction; a distribution that is not symmetric.

standard deviation - the measure of how much the values in a data set vary, or deviate, from the mean.

standard normal distribution - the normal distribution with a mean equal to 0 and a standard deviation equal to 1.

statistic - a piece of information about a variable that is based on a sample or subgroup chosen from the population

statistical question - a question that can be answered by collecting many pieces of information, or data

statistical variable - a quantity of quality that can be measured or counted, and for which data are expected to differ from one observation to another; statistical variables are either quantitative or categorical.

symmetrical distribution - a distribution with a shape that, when reflected across the mean, the display is roughly the same.

z-score - this counts how many standard deviations an individual data value is from the mean.