Psychology Statistics Exam 1

Relationship between populations and samples

Samples are drawn from a population

What is the term for the number calculated based on POPULATION data?

Parameter

What is the term for the number calculated based on SAMPLE data?

Statistic

What is the symbol for the population mean?

Mu (μ)

What is the symbol for the population standard deviation?

Sigma (σ)

What is the symbol for the sample mean?

M

What is the symbol for the sample standard deviation?

SD

What are some characteristics of nominal data? (3)

- Qualitative in nature
- Categorizes data
- Only claims differences, nothing more

What are some characteristics of ordinal data? (1)

- Rank-orders info

What are some characteristics of interval data? (3)

- Ordered
- Fixed and equal intervals
- No absolute zero means negatives are possible

What are some characteristics of ratio data? (3)

- Ordered
- Fixed intervals
- Absolute zero allows for ratio discussion

What are descriptive statistics used for?

To describe obtained data from the sample

What are inferential statistics used for?

To make inferences about the population from which the sample came

How to compute median?

Take middle point of the set of scores

What are some characteristics of the median? (2)

- Less sensitive to extreme scores
- More subject to sampling variability

When should we use the median to describe a set of scores?

With ordinal data or interval/ratio data that are skewed/have outliers

How to compute mode?

Most frequent score in data set

Characteristics of the mode?

- Most useful for values that are limited
- Not very stable/reflective of population
- Subject to sampling variability

When does the mode best describe a set of scores?

Nominal data, data that are limited

How to compute the mean?

Add all scores and divide by number of scores in set

Characteristics of the mean (5)

- Most common for central tendency
- Best for symmetrical data
- Sensitive to exact values
- Sensitive to extreme scores
- Least subject to sampling variability

How to compute overall mean?

Multiply mean by number of scores for each set, then add those and divide by sum of number of all scores

How to calculate range?

Largest score - smallest score

How to compute deviation scores?

Subtract mean from observed value for each value

How to calculate variance?

[Sum of x squared - (sum of x, squared divided by n)] divided by n-1

How to calculate standard deviation?

Square root of variance

What percentage of scores fall between the mean and one standard deviation from the mean on a normal curve in either direction?

31.43%

What percentage of scores fall between one and two standard deviations from the mean on either side on a normal curve?

13.59%

What percentage of scores fall between two and three standard deviations from the mean on either side of a normal curve?

2.15%

What percentage of scores fall beyond 3 standard deviations from the meana in either direction?

0.13%

Why are z-scores useful?

They allow us to compare data from different sets that may have different scales because they place everything on the same scale (-3 to 3). The distribution of z-scores maintains the same shape as the raw scores.

What two measurements do we need to use z-scores?

Population mean and population standard deviation

What is sampling error?

Discrepancy between sample statistic and population parameter

How do we calculate sampling error/standard error of the mean?

SEM = SD of population divided by the square root of N