24. State whether each of the following variables are examples of an independent variable or a quasi-independent variable. Remember, quasi-independent variables can’t be randomized (randomly assign participants to groups). a. marital status b. political affiliation c. time of delay prior to recall d. environment of research setting e. years of education f. type of feedback (negative, positive)
Addition Rule of Probability
It simply refers to the likelihood of an event taking place whenever the occurrence of an event is uncertain. The probability of a single event can be calculated by dividing the number of successful trials of that event by the total number of trials.
Expected Value
When a large number of trials are performed for any random variable ‘X’, the predicted result is most likely the mean of all the outcomes for the random variable and it is known as expected value also known as expectation. The expected value, also known as the expectation, is denoted by: E(X).
Probability Distributions
Understanding probability is necessary to know the probability distributions. In statistics, probability is how the uncertainty of an event is measured. This event can be anything. The most common examples include tossing a coin, rolling a die, or choosing a card. Each of these events has multiple possibilities. Every such possibility is measured with the help of probability. To be more precise, the probability is used for calculating the occurrence of events that may or may not happen. Probability does not give sure results. Unless the probability of any event is 1, the different outcomes may or may not happen in real life, regardless of how less or how more their probability is.
Basic Probability
The simple definition of probability it is a chance of the occurrence of an event. It is defined in numerical form and the probability value is between 0 to 1. The probability value 0 indicates that there is no chance of that event occurring and the probability value 1 indicates that the event will occur. Sum of the probability value must be 1. The probability value is never a negative number. If it happens, then recheck the calculation.
24. State whether each of the following variables are examples of an independent variable or a quasi-independent variable. Remember, quasi-independent variables can’t be randomized (randomly assign participants to groups).
a. marital status
b. political affiliation
c. time of delay prior to recall
d. environment of research setting
e. years of education
f. type of feedback (negative, positive)
26. Below is data that shows the number of times per day that 20 patients with obsessivecompulsive disorder washed their hands. Organize this data into a stem and leaf plot (stem and leaf display).
| 12 | 14 | 10 | 47 | 11 |
| 33 | 23 | 16 | 52 | 30 |
| 24 | 32 | 26 | 44 | 15 |
| 42 | 46 | 29 | 19 | 50 |
27. Identify the original scores in the following stem and leaf display:
Stem | Leaf
1 | 4
2 | 2 4 7
3 | 1 1 3 0 5 3
4 | 6 2 8 2 7 6 6 6 2 1
a. What is the shape of this distribution?
b. Identify the original scores in this stem and leaf display.
c. Which score in this stem and leaf display occurs most often?
28. Below is a frequency distribution table of the number of naps that mothers give their children daily.
| Number of naps | f |
| 4 | 1 |
| 3 | 8 |
| 2 | 15 |
| 1 | 8 |
| 0 | 8 |
a. What is the variable of interest?
b. What is the level of measurement of this variable?
c. What is the sample size (n)?
d. What is the most appropriate graph for this data?
e. Construct a graph of this data.
29. The following table lists the distribution by degrees in psychology conferred by degreegranting institutions, by sex and year. These and similar data are reported by the National Center of Education Statistics (NCES) at http://nces.ed.gov/programs/digest/.
| Bachelor's Degree | Males | Females |
| 1970-71 | 21,2227 | 14,602 |
| 1980-81 | 14,332 | 26,736 |
| 1990-91 | 16,067 | 42,588 |
| 2000-01 | 16,585 | 57,060 |
| 2005-06 | 19,865 | 68,269 |
Based on the data in this table, how has the number of degrees conferred in psychology changed sex since 1970-71?
30. Below is the number of hand-washing episodes 20 patients with obsessive-compulsive
disorder reported having the previous day:
21, 8, 11, 9, 12, 10, 19, 5, 9, 18,
17, 3, 6, 14, 18, 16, 19, 3, 27, 7
a. Would it be better to display this data using a simple frequency distribution data or a grouped frequency distribution table? Explain.
b. Suppose you need to create a grouped frequency distribution table for this data. Create a GFDT with five intervals.
c. Which interval had the largest frequency?
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