Social Stats

One-tailed test

- A type of hypothesis test that involves a directional research hypothesis. It specifies that the values of one group are either larger or smaller than some specific population value

Central Limit Theorem

- Basic and useful concepts of influential statistics. Tells us certain things about the nature of the sampling distribution of the mean. Holds sampling distributions approach normality as sample size increases no matter what the form of the distribution in the underlying population. Lies foundation to influential tests.

T Distribution

A family of curves, each determined by its degrees of freedom (df). It is used when the population standard deviation is unknown and the standard error is estimated from the sample standard deviation.

Population

A group that includes all the cases (individuals, objects, or groups) in which the researcher is interested

Statistic

A measure (e.g. mean or standard deviation) used to describe the sample distribution.

Parameter

A measure (e.g., mean or standard deviation) used to describe the population distribution

Probability sampling

A method of sampling that enables the researcher to specify for each case in the population the probability of its inclusion in the sample.

Estimation

A process whereby we select a random sample from a population and use a sample statistic to estimate a population parameter

Confidence interval (C.I.)

A range of values defined by the confidence level within which the population parameter is estimated to fall. Sometimes confidence intervals are referred to as margin of error.

Simple random sampling

A sample designed in such a way as to ensure that (1) every member of the population has an equal chance of being chosen and (2) every combination of N members has an equal chance of being chosen.

Point estimate

A sample statistic used to estimate the exact value of a population parameter

Null Hypothesis

A statement of "no difference" that contradicts the research hypothesis and is always expressed in terms of population parameters.

Research Hypothesis

A statement the substantive hypothesis. It is always expressed in terms of population parameters, but its specific form varies from test to test.

Sample

A subset of cases selected from a population

Sampling Distribution of the mean

A theoretical probability distribution of sample means that would be obtained by drawing from the population all possible samples of the same size.

Sampling Distribution of the difference between two means

A theoretical probability distribution that would be obtained by calculating all the possible mean differences that would be obtained by drawing all the possible independent random samples of size N1 and N2 from two population where N1 and N2 are both greater than 50.

Two-tailed test

A type of hypothesis test that involves a non- directional research hypothesis. We are equally interested in whether the values are less than or greater than one another. The sample outcome may be located at both the lower and the higher ends of the sampling distribution.

Degrees of Freedom

he numbers of scores that are free to vary in calculating a statistic.

Inferential statistics

making predictions or inferences about a population from observations based on a sample.

T statistic

the test statistic computed to test the null hypothesis about a population mean when the population standard deviation is unknown and is estimated using the sample standard deviation.

Directional Hypothesis

-are those where one can predict the direction (effect of one variable on the other as 'Positive' or 'Negative')

Z statistic

The test statistic computed by converting a sample statistic (such as the mean) to a Z score. The formula for obtaining Z varies from test to test.

Independent random sample

If the values in one sample reveal no information about those of the other sample, then the samples are...

Alpha level -

The level of probability at which the null hypothesis is rejected. It is customary to set alpha at the .05,.01, or .001 level.

Confidence level

The likelihood, expressed as a percentage or a probability, that a specified interval will contain the population parameter.

Type II error

The probability associated with failing to reject a null hypothesis when it is false.

Type I error

The probability associated with rejecting a null hypothesis when it is true.

P value/ Critical value

The probability associated with the obtained value of Z

Margin of error

The radius of a confidence interval

Sampling Distribution

The sampling distribution is a theoretical probability distribution of all possible sample values for the statistics in which we are interested.

Standard error of the mean

The standard deviation of the sampling distribution of the mean. It describes how much dispersion there is in the sampling distribution of the mean.

Pooled variance estimate

combining to variances and the difference between two means