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Thus skincare for men buy generic betnovate pills, we are 95% confident that the mean auction price for all 150-year-old clocks sold at an auction with 10 bidders lies between $1 acne treatment purchase betnovate,381 skin care olive oil best purchase betnovate. We say, with 95% confidence, that the auction price for a single 150-year-old clock sold at an auction with 10 bidders falls between $1,154. However, before we form this prediction interval, 192 Chapter 4 Multiple Regression Models Figure 4. If we want to make the prediction requested, we would need to collect additional data on clocks with the requested characteristics. As in simple linear regression, the confidence interval for E(y) will always be narrower than the corresponding prediction interval for y. This fact, however, should not drive your choice of which interval to use in practice. Use the confidence interval for E(y) if you are interested in estimating the average (mean) response; use the prediction interval for y if you want to predict a future value of the response. Recall that the researchers modeled lead-user rating (y, measured on a 5-point scale) as a function of gender (x1 = 1 if female, 0 if male), age (x2, years), degree of centrality (x3, measured as Using the Model for Estimation and Prediction 193 the number of direct ties to other peers in the network), and betweenness centrality (x4, measured as the number of shortest paths between peers). Refer to the Journal of Applied Ecology study of the feeding habits of baby snow geese, Exercise 4. Recall that a first-order model was used to relate gosling weight change (y) to digestion efficiency (x1) and acid-detergent fiber (x2). Refer to the Chance (Fall 2000) study of runs scored in Major League Baseball games, Exercise 4. Multiple regression was used to model total number of runs scored (y) of a team during the season as a function of number of walks (x1), number of singles (x2), number of doubles (x3), number of triples (x4), number of home runs (x5), number of stolen bases (x6), number of times caught stealing (x7), number of strikeouts (x8), and total number of outs (x9). Based on the model statistics, the researchers concluded that the arsenic level is highest at a low latitude, high longitude, and low depth. If so, find a 95% prediction interval for arsenic level for the lowest latitude, highest longitude, and lowest depth that are within the range of the sample data. Refer to the Journal of Engineering for Gas Turbines and Power (January 2005) study of a high-pressure inlet fogging method for a gas turbine engine, Exercise 4. An Interaction Model with Quantitative Predictors 195 (a) Interpret the 95% prediction interval for y in the words of the problem. When E(y) is graphed against any one variable (say, x1) for fixed values of the other variables, the result is a set of parallel straight lines (see Figure 4. When this situation occurs (as it always does for a first-order model), we say that the relationship between E(y) and any one independent variable does not depend on the values of the other independent variables in the model. For example, suppose that the mean value E(y) of a response y is related to two quantitative independent variables, x1 and x2, by the model E(y) = 1 + 2x1 - x2 + x1 x2 A graph of the relationship between E(y) and x1 for x2 = 0, 1, and 2 is displayed in Figure 4. You can verify that the slopes of the lines differ by substituting each of the values x2 = 0, 1, and 2 into the equation. For x2 = 0: E(y) = 1 + 2x1 - (0) + x1 (0) = 1 + 2x1 (slope = 2) 196 Chapter 4 Multiple Regression Models For x2 = 1: E(y) = 1 + 2x1 - (1) + x1 (1) = 3x1 For x2 = 2: E(y) = 1 + 2x1 - (2) + x1 (2) = -1 + 4x1 (slope = 4) Note that the slope of each line is represented by 1 + 3 x2 = 2 + x2. The cross-product term, x1 x2, is called an interaction term, and the model E(y) = 0 + 1 x1 + 2 x2 + 3 x1 x2 is called an interaction model with two quantitative variables. Suppose the collector of grandfather clocks, having observed many auctions, believes that the rate of increase of the auction price with age will be driven upward by a large number of bidders. Note that as the number of bidders increases from 5 to 15, the slope of the price versus age line increases. Consequently, the interaction model is proposed: y = 0 + 1 x1 + 2 x2 + 3 x1 x2 + Figure 4. Specifically, H0: 3 = 0 Ha: 3 > 0 Since we are testing an individual parameter, a t-test is required. The test statistic and two-tailed p-value (highlighted on the printout) are t = 6. The upper-tailed p-value, obtained by dividing the two-tailed p-value in half, is 0/2 = 0. Although the coefficient of x2 is negative, this does not imply that auction price decreases as the number of bidders increases.
Fixation-In Freudian psychoanalysis acne 7 days past ovulation buy betnovate 20 gm line, the result of overindulgence or frustration during a psychosexual stage causing a neurotic pattern of personality based on that stage acne zones and meaning cheap betnovate line. Flat affect-Behavior characterized by showing virtually no signs of emotion or affective expression skin care clinique purchase discount betnovate. Fluid intelligence-Ability to quickly identify relationships and connections, and then use those relationships and connections to make correct deductions. Forebrain-A portion of the brain that is associated with complex perceptual, cognitive, and behavioral processes such as emotion and memory. Fornix-A long projection from the hippocampus that connects to other nuclei in the limbic system. Front stage-In the dramaturgical approach, the setting where players are in front of an audience and perform roles that are in keeping with the image they hope to project about themselves. Frontal lobe-A portion of the cerebral cortex that controls motor processing, executive function, and the integration of cognitive and behavioral processes. Functional fixedness-The inability to identify uses for an object beyond its usual purpose. Functionalism-A theoretical framework that explains how parts of society fit together to create a cohesive whole. Game theory-A model that explains social interaction and decision-making as a game, including strategies, incentives, and punishments. Ganglia-Collections of neuron cell bodies found outside the central nervous system. Gemeinschaft und Gesellschaft-Theory that distinguishes between two major types of groups: communities (Gemeinschaften), which share beliefs, ancestry, or geography; and societies (Gesellschaften), which work together toward a common goal. Gender-The set of behavioral, cultural, or psychological traits typically associated with a biological sex. Generalization-In classical conditioning, the process by which two distinct but similar stimuli come to produce the same response. Gestalt principles-Ways for the brain to infer missing parts of a picture when a picture is incomplete. Globalization-The process of integrating the global economy with free trade and tapping of foreign labor markets. Group-A social entity that involves at least two people, usually those sharing common characteristics. Group polarization-The tendency toward decisions that are more extreme than the individual inclinations of the group members. Groupthink-The tendency for groups to make decisions based on ideas and solutions that arise within the group without considering outside ideas and ethics; based on pressure to conform and remain loyal to the group. Hallucinations-Perceptions that are not due to external stimuli but have a compelling sense of reality. Heterosexual-A sexual orientation wherein individuals are attracted to members of the opposite sex. Hindbrain-A portion of the brain that controls balance, motor coordination, breathing, digestion, and general arousal processes. Hippocampus-A portion of the limbic system that is important for memory and learning. Homosexual-A sexual orientation wherein individuals are attracted to members of the same sex. Hypnagogic hallucinations-Hallucinations that occur when going to sleep; seen in narcolepsy. Hypnopompic hallucinations-Hallucinations that occur when awakening from sleep; seen in narcolepsy. Hypnosis-An altered state of consciousness in which a person appears to be awake but is, in fact, in a highly suggestible state in which another person or event may trigger action by the person. Hypothalamus-A portion of the forebrain that controls homeostatic and endocrine functions by controlling the release of pituitary hormones.
The values of these two variables are used to acne jensen boots sale cheap 20 gm betnovate amex compute a driving performance index skin care qualifications betnovate 20 gm with visa. Use simple linear regression skin care 1 buy 20 gm betnovate with amex, where y = driving accuracy and x = driving distance, to answer the question. The importance of having employees with a healthy worklife balance has been recognized by U. For example, a chain of convenience stores may be interested in modeling sales y of a new diet soft drink as a linear function of amount x of the new product in stock for a sample of stores. Or, a medical researcher may be interested in the linear relationship between dosage x of a drug for cancer patients and increase y in pulse rate of the patient 1 minute after taking the drug. The convenience store chain knows that if one of its stores chooses not to stock the new diet soft drink, it will have zero sales of the new product. Likewise, if the cancer patient takes no dosage of the drug, the theoretical increase in pulse rate 1 minute later will be 0. For situations in which we know that the regression line passes through the origin, the y-intercept is 0 = 0 and the probabilistic straight-line model takes the form y = 1 x + When the regression line passes through the origin, the formula for the least squares estimate of the slope 1 differs from the formula given in Section 3. Several other formulas required to perform the regression analysis are also different. This is because we need to estimate only a single parameter 1 rather than both 0 and 1. Consequently, we have one additional degree of freedom for estimating 2, the variance of. Tests and confidence intervals for 1 are carried out exactly as outlined in the previous sections, except that the t distribution is based on (n - 1) df. Tests and Confidence Intervals for Regression Through the Origin Test statistic for H0: 1 = 0: t= ^ 1 - 0 = s 1 ^ ^ 1 s/ s xi2 xi2 100(1 -)% confidence interval for 1: ^ ^ 1 ± (t/2)s1 = 1 ± (t/2) ^ 100(1 -)% confidence interval for E (y): xp xi2 y ± (t/2)sy = y ± (t/2)s ^ ^ ^ 100(1 -)% prediction interval for y: y ± (t/2)s(y-y) = y ± (t/2)s ^ ^ ^ where the distribution of t is based on (n - 1) df 1+ 2 xp xi2 Example 3. In one experiment, samples of cadmium were deposited in a small graphite tube and then heated until vaporization. Researchers have discovered that the amount of light absorbed (y) can be linearly correlated to the concentration (x) of cadmium present in the graphite tube. Thus, we predict with 95% confidence that the amount of light absorbed for a cadmium specimen with a concentration of 18 ng/ml will fall between. Caveat #1: the value of the coefficient of determination, r 2, for the regressionthrough-the-origin model E(y) = 1 x is computed as follows: r2 = 1 - ^ (yi - yi)2 yi2 146 Chapter 3 Simple Linear Regression Recall, from Section 3. Consequently, one should not attempt to compare directly the r 2 values from models with and without a y-intercept. No longer can we state that r 2 measures a percentage reduction in sum of squared errors, since the denominator does not represent the sum of squared errors for the model E(y) = 0. Caveat #2: There are several situations where it is dangerous to fit the model E(y) = 1 x. If you are not certain that the regression line passes through the origin, it is a safe practice to fit the more general model E(y) = 0 + 1 x. If the line of means does, in fact, pass through the origin, the estimate of 0 will differ from the true value 0 = 0 by only a small amount. For all practical purposes, the least squares prediction equations will be the same. On the other hand, you may know that the regression passes through the origin (see Example 3. Yet, we often fit a linear model to the data in such situations because we believe that a straight line will make a good approximation to the mean response E(y) over the region of interest. The problem is that this straight line is not likely to pass through the origin (see Figure 3. By forcing the regression line through the origin, we may not obtain a very good approximation to E(y). For these reasons, regression through the origin should be used with extreme caution. Initially, the company considered the model y = 1 x + since, in theory, a patient who receives a dosage of x = 0 should show no decrease in pulse rate (y = 0). Consider the relationship between the total weight of a shipment of 50-pound bags of flour, y, and the number of bags in the shipment, x. Hence, the appropriate model might be y = 1 x + From the records of past flour shipments, 15 shipments were randomly chosen and the data in the following table recorded.
Thus skin care vegetables discount betnovate 20 gm without prescription, an implicit selfesteem score (x1) and explicit self-esteem score (x2) was obtained for each acne canada scarf purchase 20 gm betnovate with mastercard. Finally skin care insurance buy discount betnovate 20 gm on-line, the researchers computed two measures of accuracy in estimating implicit self-esteem: y1 = (x3 - x1) and y2 = x3 - x1. Refer to the Environmental Science and Technology (January 2005) study of the reliability of a commercial kit to test for arsenic in groundwater, Exercise 4. Refer to the Journal of Colloid and Interface Science study of water/oil mixtures, Exercise 4. Recall that three of the seven variables used to predict voltage (y) were volume (x1), salinity (x2), and surfactant concentration (x5). Discuss how these interaction terms affect the hypothetical relationship between y and x1. Does this model appear to fit the data better than the first-order model in Exercise 4. In this section, we consider a model that allows for curvature in the relationship. The form of this model, called the quadratic model, is y = 0 + 1 x + 2 x 2 + the term involving x 2, called a quadratic term (or second-order term), enables us to hypothesize curvature in the graph of the response model relating y to x. Graphs of the quadratic model for two different values of 2 are shown in Figure 4. The physiologist theorizes that the amount of immunoglobulin y in blood (called IgG, an indicator of long-term immunity) is related to the maximal oxygen uptake x (a measure of aerobic fitness level) of a person by the model y = 0 + 1 x + 2 x 2 + To fit the model, values of y and x were measured for each of 30 human subjects. The figure illustrates that immunity appears to increase in a curvilinear manner with fitness level. This provides some support for the inclusion of the quadratic term x 2 in the model. The least squares estimates of the ^ parameters (highlighted at the bottom of the printout) are 0 = -1,464. A numerical 2 measure of fit is obtained with the adjusted coefficient of determination, Ra. First, the estimated y-intercept, 0, can be meaningfully interpreted only if the range of the independent variable includes zero-that ^ is, if x = 0 is included in the sampled range of x. The estimated coefficient of the first-order term x will not, in general, have a meaningful interpretation in the quadratic model. In fact, the concavity of the model would lead to decreasing usage estimates if we were to display the model out to x = 120 and beyond (see Figure 4. However, model interpretations are not meaningful outside the range of the independent variable, which has a maximum value of 69. Thus, although the model appears to support the hypothesis that the rate of increase of IgG with maximal oxygen uptake decreases for subjects with aerobic fitness levels near the high end of the sampled values, the conclusion that IgG will actually begin to decrease for very large aerobic fitness levels would be a misuse of the model, since no subjects with x-values of 70 or more were included in the sample. Thus, the slope varies as a function of x, rather than the constant slope associated with the straight-line model. For any reasonable, we reject H0 and conclude that the overall model is a useful predictor of immunity level, y. Thus, there is very strong evidence of downward curvature in the population, that is, immunity level (IgG) increases more slowly per unit increase in maximal oxygen uptake for subjects with high aerobic fitness than for those with low fitness levels. Since the interpretation of these parameters is not meaningful for this model, the tests are not of interest. Management professors at Columbia University examined the relationship between assertiveness and leadership (Journal of Personality and Social Psychology, February 2007). Based on answers to a questionnaire, the researchers measured two variables for each subject: assertiveness score (x) and leadership ability score (y). Refer to the Geographical Analysis (January 2007) study that demonstrated the use of satellite image maps for estimating urban population, Exercise 4. A first-order model for census block population density (y) was fit as a function of proportion of block with lowdensity residential areas (x1) and proportion of block with high-density residential areas (x2). Carp were divided into groups of 215 fish, each according to body weight and each group placed in a separate tank. The carp were then fed a proteinfree diet three times daily for a period of 20 days. A quadratic model was applied to motor vehicle toxic emissions data collected over 15 recent years in Mexico City (Environmental Science and Engineering, September 1, 2000). The following equation was used to predict the percentage (y) of motor vehicles without catalytic converters in the Mexico City fleet for a given year (x): y = 325,790 - 321.