Monday, March 18, 2013

Individual Text Assignment


12. Explain and give an example for each of the following types of variables: (a) equal-interval, (b) rank-order, (c) nominal, (d) ratio scale, (e) continuous.
(a) An equal-interval variable is variable by which numbers represent numbers stand for almost exact equal amounts of what is being measured (Aron, Aron, & Coups, 2009). An example is the difference between stress ratings of 2 and 4 means about as much as the difference between 5 and 7. (b) A rank-order or ordinal variables is a variable by which numbers stand for relative ranking only (Aron, Aron, & Coups, 2009). An example is a car models’ standing in a safety class ranking. (c) Nominal variable is a variable by which the values are categories or names (Aron, Aron, & Coups, 2009). An example is the nominal variable student; the values are traditional and nontraditional. (d) A ratio scale is a scale of measurement of data, which allows comparisons of the differences of values. An example is the time measured from the "Big Bang" until present is on a ratio scale, because before the “Big Bang” time had not begun on Earth. (e) Aron, Aron, and Coups (2009), “with a continuous variable, there are in theory an infinite number of values between any two values” (p. 4). An example is measuring height because the variables would be continuous. There are an unlimited number of possibilities of height even when only looking at between 4 and 5.2 feet.
15. Following are the speeds of 40 cars clocked by radar on a particular road in an 35-mph zone on a particular afternoon:
30, 36, 42, 36, 30, 52, 36, 34, 36, 33, 30, 32, 35, 32, 37, 34, 36, 31, 35, 20,
24, 46, 23, 31, 32, 45, 34, 37, 28, 40, 34, 38, 40, 52, 31, 33, 15, 27, 36, 40
Make (a) a frequency table and (b) a histogram. Then (c) describe the general shape of the distribution.
(a)    Frequency Table
SPEED
FREQUENCY
PERCENTAGE
15-19
1
2.5
20-24
3
7.5
25-29
2
5
30-34
15
37.5
35-39
11
27.5
40-44
4
10
45-49
2
5
50-54
2
5

(b) Histogram



(c) The general shape of distribution is unimodal.
19. Give an example of something having these distribution shapes: (a) bimodal, (b) approximately rectangular, and (c) positively skewed. Do not use an example given in this book or in class.
(a) Bimodal: an example is a day’s account of new drivers taken the written examination driver test. The majority of participants scored between 85-98%, the second largest category of participants scored between 84-88%, and the remainder of participants scored inconsistently between 55% and 99%.  
(b) Approximately rectangular: an example is an online college classroom of 25 traditional and nontraditional students. 15 of the students were 19 years of age and 10 were 32 years of age, which generates a rectangular distribution.
 (c) Positively skewed: an example is a case study of 25 college seniors, whereas one computes the hours of study spent on coursework daily, which may show positively skewed distribution. In this case study 10 students spent 2-3 hours studying daily, 11 spent 3 hours studying daily, and 3 students spent 4-5 hours studying daily. Giving outcomes positively skewed.   
20. Find an example in a newspaper or magazine of a graph that misleads by failing to use equal interval sizes or by exaggerating proportions.

This graph shows the stock market plummeted the day after President Barack Obama’s re-election but it does not show the trend of losses before the President’s re-election. The plummet started on May, 2008, which is not indicated. This leads individuals to believe the drop resulted from President Barack Obama’s re-election.
21. Nownes (2000) surveyed representatives of interest groups who were registered as lobbyists of three U.S. state legislatures. One of the issues he studied was whether interest groups are in competition with each other. Table 1–10 shows the results for one such question. (a) Using this table as an example, explain the idea of a frequency table to a person who has never had a course in statistics. (b) Explain the general meaning of the pattern of results.
(a) Frequency tables are used to explain data gathered and are a way to display certain factors present. These tables are used to find the mean of a large set of data values. In table 1-10, what is demonstrated is what the specific group encounters competition. 20% experiences no competition, 58% experiences some competition, and 22% experiences a lot of competition. (b) The general meaning of the pattern of results from table 1-10, shows results split up exhibiting a specific frequency of a group which encounters rivalry from similar groups. All responses are represented in percentage and number patterns, which indicate the relationship occurring between the groups.    
22. Mouradian (2001) surveyed college students selected from a screening session to include two groups: (a) “Perpetrators”—students who reported at least one violent act (hitting, shoving, etc.) against their partner in their current or most recent relationship—and (b) “Comparisons”—students who did not report any such uses of violence in any of their last three relationships. At the actual testing session, the students first read a description of an aggressive behavior such as, “Throw something at his or her partner” or “Say something to upset his or her partner.” They then were asked to write “as many examples of circumstances of situations as [they could] in which a person might engage in behaviors or acts of this sort with or towards their significant other.” Table 1–11 shows the “Dominant Category of Explanation” (the category a participant used most) for females and males, broken down by comparisons and perpetrators. (a) Using this table as an example, explain the idea of a frequency table to a person who has never had a course in statistics. (b) Explain the general meaning of the pattern of results.
(a) The information in the frequency table explains by sorting the data briefly and clearly. The table exhibits frequency and the percentage of occurrences team members, male and female experienced in each category situation.
(b) The general meaning of the results shows the trend of outcomes for the table, whereas the majority of women perpetrators (27%) display intimate aggression because of control motives, and the majority of men perpetrators (31%) display expressive aggression. The combined majority of intimate aggression of men and women was rejection of perpetrator or act with 46%, and the combined lowest of intimate aggression of men and women was prosocial/acceptable explanations with 0%.

Clark, P. (2012). The New York Observer. Retrieved from http://observer.com/2012/11/stocks-fall-on-day-after-obama-reelection-but-not-as-far-as-in-2008/

Why do researchers use nonparametric tests? Describe a psychological research situation or scenario that would use a nonparametric test. Why would the nonparametric test be used?


     Nonparametric tests (distribution free tests) are statistical tests, which can be used with data and with skewed distributions at the nominal or ordinal level of measurement (Weaver, 2002). The reason they are also called distribution free tests is because the assumptions underlying their use are weaker and fewer than the assumptions associated with parametric tests (Weaver, 2002). Nonparametric tests barely require any assumptions concerning the shapes of the underlying population distributions (Weaver, 2002). Which is why nonparametric test are used instead of parametric tests if the assumptions of the parametric test have been grossly violated (Weaver, 2002). Nonparametric test are also referred to as rank-order tests because rank or ordinal data usually requires nonparametric analysis. Researchers use nonparametric tests when certain assumptions cannot be made about the population and when the type of data is ordinal in nature and not at least interval. A psychological research situation where the effects of deliberately induced stress on participants could be ranked according to how fast each participant recovers to a normal stress free state (first, second third, and so forth) and ranked on how accurately they perform test right after stress is induced (first, second third, and so forth). 
 Reference
 Weaver, B. (2002). Angelfire. Retrieved from http://www.angelfire.com/wv/bwhomedir/notes/nonpar.pdf

What is an analysis of Variance (ANOVA) and when would a researcher use ANOVA for data analysis? Provide an example. What are post hoc comparisons and why are they conducted?


     An analysis of Variance (ANOVA) is a statistical procedure, which is for testing variation among the means of more than two groups, and is used for the study of two groups (Aron, Aron, & Coups, 2009). To determine if there is a difference on some variable between two or more groups a researcher uses ANOVA. ANOVA is a technique, which can be used to test the hypothesis that the means among two or more groups are equal, under an assumption that the sampled populations are normally distributed (Aron, Aron, & Coups, 2009). ANOVA is equivalent to more than one t-tests, therefore compare the means of three groups is easily accomplished with conducting a 1-way ANOVA with the three groups instead of conducting three different t-test. An example of using ANOVA is when conducting a one-way ANOVA to determine if there are significant differences between the reading levels of a set of triplets in fifth grade in three different english classes of the same school. These three environments (three different classes) form the three levels of the factor. Post hoc comparisons are several comparisons, which are not specified in advance (Aron, Aron, & Coups, 2009). After an analysis of variance post hoc comparisons are conducted as part of an exploratory analysis (Aron, Aron, & Coups, 2009).  
 Reference
 Aron, A., Aron, E. N., & Coups, E. (2009). Statistics for psychology (5th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

Sunday, March 10, 2013

What do the terms variance and standard deviation mean? How are these concepts related? How are they calculated?

     Variability refers to how spread out or closely clustered a set of data is. Variability has two measures, which are variance and standard deviation. A group of scores' variability can be described by the variance and the standard deviation (Aron, Aron, & Coups, 2009). The term variance, which is represented by the symbol (σ2), is the average of the squared deviation of each score from the mean or how far numbers lie from the mean (Aron, Aron, & Coups, 2009). The term standard deviation, which is represented by the symbol sigma (σ), is displays how much variation exists from the average or mean. When data points tend to be close to the mean this is referred to as a low standard deviation and when data points are spread out over a large range of values this is referred to as a high standard deviation. Variance and standard deviation are related because standard deviation is the square root of the variance, which is  (Aron, Aron, & Coups, 2009). 
represents variance, which is calculated by finding the variance then by finding the square root.
represents standard deviation, which is calculated by taking the sum of the squares of the terms in the distribution, and divide by the number of terms in the distribution, and then subtract the square of the mean. 
Reference
Aron, A., Aron, E. N., & Coups, E. (2009). Statistics for psychology (5th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

When is the mean the best measure of central tendency? When is the median the best measure of central tendency?


     Central tendency relates to the way in which quantitative data tend to cluster around some value. Central tendency has three measures, which is any of a number of ways of specifying central value. The mean is one of the three measures of central tendency, which is best measure when the distribution of data is continuous and symmetrical. It is the ordinary average, the sum of all the scores divided by the number of scores (Aron, Aron, & Coups, 2009). Therefore to find the mean one can add six numbers then divided by six, which represents the amount of numbers added. The median, an alternative to the mean is another of three measures of central tendency, which is the best measure when data is skewed.
To find the median one must line up all the scores from lowest to highest, then add 1 to the number of scores and dividing by 2, and count up to the middle score or scores (Aron, Aron, & Coups, 2009). The mode is the last of the three measures of central tendency, which is the most frequently occurring score.    
 Reference 
Aron, A., Aron, E. N., & Coups, E. (2009). Statistics for psychology (5th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.

What is the difference between a one-tailed and a two-tailed test of significance? Under what circumstances would each be used?


     The difference between a one-tailed and two-tailed test of significance is that a one-tailed test looks for an increase or decrease in the parameter and a two-tailed test looks for any change in the parameter (Stockburger, n.d.). The one-tailed hypothesis-testing procedure is for a directional hypothesis and the two-tailed hypothesis-testing is a procedure for a nondirectional hypothesis. A one- or two-tailed t-test is determined by whether the total area of a is placed in one tail or divided equally between the two tails (Stockburger, n.d.). When the results are interesting only if they turn out in a particular direction a one-tailed test is performed and  if the results would be interesting in either direction a two-tailed test is performed. In a one-tailed test the area associated with a is in either one tail or the other, and the selection of the tail depends which direction would be positive or negative (Stockburger, n.d.) A two-tailed test divides a in half by placing half in the each tail, therefore the null hypothesis is a particular value with two alternative hypotheses, one positive and one negative (Stockburger, n.d.). The hypothesis-testing procedure is effected in different ways depending on the choice of one- or two-tailed tests.
Reference
 Stockburger, D.W. (n.d.). Introductory Statistics: Concepts, Models, and Applications . Retrieved from http://www.psychstat.missouristate.edu/introbook/sbk25m.htm

How do researchers determine whether or not to reject the null hypothesis?


     A null hypothesis is a statement about a relation between populations that is the opposite of the research hypothesis (Aron, Aron, & Coupe, 2009). A research hypothesis is the exact opposite of a null hypothesis. In statistics, for one to support their hypothesis he or she must refute the null hypothesis. Instead of one proving their idea (alternate hypothesis) right, he or she needs to show that the null hypothesis is likely going to be wrong, as in to nullify or refute the null hypothesis ("Null Hypothesis", n.d.). One must assume his or her alternate hypothesis to be incorrect until they find contrary evidence. Researchers determine whether or not to reject the null hypothesis through the hypothesis-testing process. The hypothesis-testing process has five steps, which are (1) restate the question as a research hypothesis and a null hypothesis about the populations, (2) determine the characteristics of the comparison distribution, (3) determine the cutoff sample score on the comparison distribution at which the null hypothesis should be rejected, (4) determine your sample’s score on the comparison distribution, and (5) decide whether to reject the null hypothesis. The hypothesis-testing process is formal procedure used to accept or reject the null hypotheses. 
Reference
 Null Hypothesis. (n.d.). Retrieved from http://www.null-hypothesis.co.uk/science/item/what_is_a_null_hypothesis/
Aron, A., Aron, E. N., & Coups, E. (2009). Statistics for psychology (5th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.