Psy 230: Psychological Measurement & Statistics Study guide #1

What is the difference between random sampling and haphazard sampling?

A random sample is when you choose a sample completely at random from a population. All members of population have equal chance of being in the sample A haphazard sample is when you draw a sample from a convenient/available participant.

What is the difference between a sample and a population?

A sample is the subset of population that actually participates in our study and A population is the entire set of things of interest. Entire group of people we want to make a statement about. The group we are interested in

• Define the following types of variable: Numeric (quantitative) variable, Discrete Variable, Continuous variable, Equal-interval variable, Rank order variable, Nominal (categorical) variable

Discrete variable: variables that has specific values and that cannot have values between these specific values. #s cannot fall in the middle continuous variable: infinite possible values between 2 values equal-interval variable: is a variable in which the numbers stand for approximately equal amounts of what is being measured Rank order variable: is a variable in which the numbers stand only for relative ranking. Like where your class standing is when you graduate. o Nominal (categorical) variable: which variables are names or categories?

Kurtosis

Extent to which a frequency distribution deviates from a normal curve in terms of whether its curve in the middle is more peaked or flat than the normal curve.

4 steps to figure the variance

1. subtract the mean from each score (gives score's deviation score) 2. square each of these deviation score (gives score's squared deviation score) 3. add up the squared deviation scores (gives sum of squared deviation= SS) 4, divide the sum of squared deviation by the number of scores (gives average of the squared deviation, variance)

What is a Z score?

A Z score is a number of standard deviations that a score is above or below if it is negative the mean of its distribution; it is thus an ordinary score transformed so that it better describes the score's location in a distribution

What is a histogram?

A histogram is one kind of graph of the information in a frequency table which kind of a bar chart.

What is central tendency?

Central tendency is statistics that indicate typical "central" values of distribution. They are numbers that try to represent the group in some way. EX: pop quiz score of 70% is that a good score?

Why is it useful to convert raw scores into Z scores?

It allows you to compare the scores to normal population

What are statistics?

Mathematical branch focused, organization, analysis, and interpretation of numbers

5 steps of hypothesis testing

Step 1: restate question as research hypothesis & null hypothesis about populations Step 2: Determine the characteristics of the comparison distribution Step 3: Determine the cutoff sample score on the comparison distribution at which the null hypothesis should be rejected Step 4: Determine your sample's score on the comparison distribution. Step 5: Decide whether to reject the null hypothesis.

What is variability?

a variability is how spread out a distribution's scores are. the amount of spread of scores around the mean. Most scores close to mean=low variability. Most scores further from mean= high variability

Variance

average of the squared deviation scores. 2 steps to figure standard deviation. • Figure the variance • Take the square root

Statistical Significance

if its score is extreme enough to reject the null hypothesis. Most psychologists research uses cutoff of 5% (p< .05)

Median

middle score when all scores in distribution are arranged from lowest to highest. odd number of scores: median=middle number. even number of scores: median= average of 2 middle scores

Mode

most common score in the distribution. the one that shows up the most. Peak of the histogram

Mean

numerical average of distribution. Its most commonly used measure of central tendency. sum of all scores divided by number of scores

What are differences between descriptive statistics and inferential statistics?

o A descriptive statistics is procedures for summarizing a group of scores or otherwise making them more understandable and an o Inferential statistics is procedures for drawing conclusions based on the scores collected in a research study but going beyond them.

What is a frequency table?

o A frequency is the number of times the data value occurs o For example, if four students have a score of 80 in mathematics, and then the score of 80 is said to have a frequency of 4. o A frequency table is constructed by arranging collected data values ascending order of magnitude with their corresponding frequencies. Be able to create a frequency table from a given set of data.

What is the difference between a one-tailed test and a two-tailed test?

o A one tailed is the hypothesis test in which region of comparison distribution in which null hypothesis is rejected is all on one side (tail) of the distributions o A two tailed-test is when you divide significance percentage between the two tails. Only reject null hypothesis if sample falls in top/bottom 2.5%

Describe the difference between a sample statistics and population parameters

o A sample statistics is descriptive statistics figured for scores in a sample (known descriptive sample) o Population parameters: is mean, variance, SD for the population (usually unknown, inferred from sample) be sure to know the symbols used in formulas for each.

What is the major question we are trying to answer when hypothesis testing?

o The major question we are trying to answer is: Is the sample data typical of the general population, or is it very different than most of the population? o If very different=sample not likely to be part of that population (sample ended up different somehow) o If more typical-inconclusive, the more similar our hypothesis is, the less we are able to make it

Describe the following ways in which distributions can vary: Unimodal, Bimodal, Rectangular distribution, Symmetrical Vs. Skewed distributions

o Unimodal A unimodal gives a graph only one very high area. o Bimodal A Bimodal has two fairly equal high points o rectangular distributions a rectangular has values of all about the same frequency o symmetrical vs. skewed distributions Symmetrical: distribution in which the pattern of frequencies on the left and right side are mirror images of each other Skewed: distribution in which the scores pile up one side of the middle and are spread out on the other side; distribution that is not symmetrical

Null Hypothesis

opposite of research hypothesis. It predicts no difference/opposite result. Population 1 will not have a higher IQ than population 2. Researchers try to disprove (reject) null hypothesis

cutoff sample score

point on comparison distribution at which, if reached or exceeded by the sample, you reject the null hypothesis

Research hypothesis

prediction about relationship between populations (alternative hypothesis). Usually predicts differences between population means, population 1 will have higher IQ than population 2

Why do we usually conduct research on samples?

we study samples instead of populations because it's impractical to study entire populations

what is a probability?

Probability is the expected relative frequency of an outcome of a component. Be able to figure the probability of a given outcome from a data set.

Why are they important for conducting psychological research?

Psychologists use statistical methods to help them make sense of the numbers they collect when conducting research.

What does it mean to reject the null hypothesis?

Rejecting the null hypothesis mean the lower probability of result happening by chance-significant result. Result support research hypothesis but do not necessarily prove it be true.

What does it mean to fail the null hypothesis?

Substantial probability as defined by step 3. Doesn't mean that research hypothesis is wrong. If the results was not statistically significant-inconclusive result

Describe hypothesis testing

Systematic way of determining whether data from (sample) support prediction (about population)

What is the normal curve/normal distribution?

The normal curve is a distribution of many psychological variables= roughly "normal distribution"

Range

difference between lowest score and highest score in distribution Ex: small range: lowest score=590, highest=610 610-590=20

Comparison Distribution

distribution that represents population if the null hypothesis is true. Distribution that you compare the sample data to. Known normal distribution with mean=100 SD=15