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PSYC Quiz 1 review
Review for quiz 1
| Question | Answer |
|---|---|
| Independent variables (IV; e.g., method): | Is manipulated (IV is what makes the research groups differ) |
| Dependent variables (DV; e.g., grades): | Is the measured outcome |
| Variables can be measured on four scales: | 1. Nominal 2. Ordinal 3. Interval 4. Ratio |
| Ordinal scale: | consists of categories organized in order of magnitude, but differences between values may be arbitrary. e.g., football rankings, drink sizes (small, medium, large) |
| Nominal scale: | consist of categories used to identify subjects, but that do not differ in magnitude. (e.g., religions, football jersey numbers, area codes) |
| Interval scale: | consists of ordered categories that contain intervals that are all equal (may have negative numbers) (e.g., temperature, rating scale ranging from -2 to +2) |
| Ratio scale: | is an interval level scale with an absent zero point, such as that zero reflects an absence of that variable. (e.g., number of children a person has, years in college) |
| X: | Generally refers to scores on variable X. (similarly, Y refers to scores on variable Y) |
| Σ (sigma): | represents “the sum of” (e.g., ΣX means add up all the scores for variable X) |
| N: | reflects the number of observations in a population |
| n: | reflects the number of observations in a sample |
| Absolute frequency: | the number of observations in a given statistical category. |
| Frequency distribution: | An organized tabulation of the number of individuals located in each category on the scale of measurement. |
| ______ _______ provide summaries of data to identify any patterns. | Descriptive statistics |
| Relative frequency (rf): | Number of scores in a given category (or of a given value) divided by the total number of observations. f= f/N Reflects proportion of all scores in that category. Sum of all rfs, added up to 1.00 (reflecting 100% of scores) |
| Cumulative frequency (cf): | Sum of the absolute frequencies below and including that category (how many were at that score or below) (ch. 2, slide 5) |
| For frequency distribution graphs each graph has two perpendicular lines: | 1.Horizontal X-axis (or abscissa) with X-values 2.Vertical Y-axis (or ordinate) with frequencies) |
| Unlike in tables, need to include all values of X in between highest and lowest scores in data set, for what 2 types of graphs? | Frequency histograms Frequency polygons |
| Nearly all distributions shape can be classified as being either symmetrical or skewed. | Symmetrical; skewed |
| Symmetrical distribution: | it is possible to draw a vertical line through the middle so that one side of the distribution is a mirror image of the other (figure 2.11, p. 50) |
| Skewed distribution: | the scores tend to pile up toward one end of the scale and taper off gradually at the other end (figure 2.11, p. 50) |
| Positively skewed: | most scores are very low, the peak is on the left side, the tail on the right side. (Which score is doing the skewing? which score is the least common?) (Usually the mean will be HIGHER than the median and mode) |
| Negatively skewed: | most scores are positive or high. The few negative scores or closer to negative, are skewing. (Which score is doing the skewing? which score is the least common?) (usually the mean will be LOWER than the median and mode) |
| Central tendency: | Statistical measure to determine the center or middle of the data. Goal is to find a value that is most representative or typical of the group. |
| Measures of central tendency: | Mean, median, and mode |
| Mean: | Reflects the arithmetic average of a data set. Typically, the preferred measure because it uses all the scores. |
| The population mean, µ, is calculated as follows: | μ= ΣX/N |
| μ= ΣX/n : | The sample mean, M |
| Characteristics of the mean: | -Changing, or adding, or removing, one score changes the mean. -Adding, subtracting, dividing, or multiplying each score by a constant value changes the mean in the same way -(if you add two years to everyone’s age, the mean would be two years higher) |
| The only number that won’t change the mean is: | The exact number of the mean. |
| Median: | divides a distribution of scores exactly in half. 50% of scores at or below median, and 50% at or above it. •Finding the sample median, symbolized by Mdn •Depends on only one or two scores, but is a good estimate of middle when the distribution is s |
| How do you find the median if n is odd? | put scores in order form least to greatest, and the median is the middle score: 6, 10, 5, 2, 8 •2, 5, 6, 8, 10 median = 6 |
| If n is even, how do you find the median? | put scores in order, and the median is the average of the two middle scores: 8, 10, 5, 11, 2, 6 •2, 5, 6, 8, 10, 11 •6+8 = 14/2 = 7 median = 7 |
| Median position: | if a decimal, take mean as above) •MdnPas = (n+1)/2 •2, 5, 6, 8, 10 •(5+1)/2 → 6/2 → 3 = Mdn = 3rd from left. Mdn = 6 |
| Mode: | The most frequent score in a data set. •Mode is the oly measure of central tendency that can be used when the X-variable is nominal. •It is possible to have more than one mode. •bimodal and multimodal distributions |
| Variability: | a quantitative measure of the degree to which scores in a distribution are spread out. •If most scores hover around the mean, there is low variability (and no variability if all scores are the same) •The value will equal zero if all scores are the s |
| How do you find the mode? | just look at the frequencies of each score (or category) and identify the score with the greatest frequency. |
| Range: | A simple measure of variability. Largest score minus the smallest score. |
| Standard deviation: | The most commonly reported measure of variability. It uses the mean as a reference point and measures the distance of each score from the mean. It measures the average distance from the mean. |
| Four steps to finding standard deviation: | 1.Find deviation of each score from the mean (X-µ) 2.Calculate mean deviation score, but Σ(X-µ)=0 3.So, square deviations and find mean squared value Σ(X-µ)2/N •This value is called the population variance, symbolized by σ2 4.To find standard (deviat |
Created by:
kenjaroni