405 ECONOMETRICSChapter # 0: Introduction

By: Domodar N. Gujarati

Prof. M. El-SakkaProf. M. El-SakkaDept of Economics: Kuwait UniversityDept of Economics: Kuwait University

WHAT IS ECONOMETRICS?

• Econometrics means “Econometrics means “economic measurementeconomic measurement”. the scope of ”. the scope of econometrics is much broader, as can be seen from the following econometrics is much broader, as can be seen from the following definitions: definitions:

• ““Consists of Consists of the application of mathematical statistics the application of mathematical statistics to economic to economic data to lend empirical support to the models constructed by data to lend empirical support to the models constructed by mathematical economics and to mathematical economics and to obtain numerical resultsobtain numerical results” (Gerhard ” (Gerhard 1968). 1968).

• ““Econometrics may be defined as the social science in which the tools Econometrics may be defined as the social science in which the tools of economic theory, mathematics, and statistical inference are of economic theory, mathematics, and statistical inference are applied to the applied to the analysis of economic phenomenaanalysis of economic phenomena” (Goldberger 1964).” (Goldberger 1964).

• ““Econometrics is concerned with the Econometrics is concerned with the empirical determination empirical determination of of economic lawseconomic laws” (Theil 1971).” (Theil 1971).

WHY ECONOMETRICS IS A SEPARATE DISCIPLINE?

• the subject deserves to be studied in its own right for the following the subject deserves to be studied in its own right for the following reasons:reasons:

• Economic theory makes Economic theory makes statements or hypotheses statements or hypotheses that are mostly that are mostly qualitativequalitative in nature (the law of demand), the law does not provide in nature (the law of demand), the law does not provide any any numericalnumerical measure of the relationship. This is the job of the measure of the relationship. This is the job of the econometrician. econometrician.

• The main concern of The main concern of mathematical economicsmathematical economics is to express economic is to express economic theory in mathematical form without regard to theory in mathematical form without regard to measurabilitymeasurability or or empirical verification of the theory. Econometrics is mainly empirical verification of the theory. Econometrics is mainly interested in the interested in the empirical verification empirical verification of economic theory. of economic theory.

• Economic statistics Economic statistics is mainly concerned with collecting, processing, is mainly concerned with collecting, processing, and presenting economic data in the form of charts and tables. It and presenting economic data in the form of charts and tables. It does does not go any furthernot go any further. The one who does that is the . The one who does that is the econometrician. econometrician.

METHODOLOGY OF ECONOMETRICS

• Broadly speaking, traditional econometric methodology proceeds Broadly speaking, traditional econometric methodology proceeds along the following lines:along the following lines:

1. Statement of theory or 1. Statement of theory or hypothesishypothesis..

2. Specification of the 2. Specification of the mathematical model mathematical model of the theoryof the theory

3. Specification of the statistical, or 3. Specification of the statistical, or econometriceconometric, model, model

4. Collecting the 4. Collecting the datadata

5. Estimation of the 5. Estimation of the parametersparameters of the econometric model of the econometric model

6. Hypothesis 6. Hypothesis testingtesting

7. Forecasting or 7. Forecasting or predictionprediction

8. Using the model for control or 8. Using the model for control or policy purposes.policy purposes.

• To illustrate the preceding steps, let us consider the well-known To illustrate the preceding steps, let us consider the well-known Keynesian theory of consumption.Keynesian theory of consumption.

1. Statement of Theory or Hypothesis1. Statement of Theory or Hypothesis• Keynes states that on average, consumers increase their consumption as Keynes states that on average, consumers increase their consumption as

their income increases, but not as much as the increase in their income their income increases, but not as much as the increase in their income (MPC < 1).(MPC < 1).

2. Specification of the Mathematical Model of Consumption (single-2. Specification of the Mathematical Model of Consumption (single-equation model)equation model)

Y = βY = β11 + β + β22X 0 < βX 0 < β22 < 1 < 1 (I.3.1)(I.3.1)

Y = consumption expenditure and (Y = consumption expenditure and (dependent variable)dependent variable)

X = X = income, (independent, or explanatory variable)income, (independent, or explanatory variable)

ββ11 = = the intercept the intercept

ββ22 = = thethe slope coefficientslope coefficient

• The slope coefficient The slope coefficient ββ22 measures the MPC. measures the MPC.

• GeometricallyGeometrically,,

3. 3. Specification of the Econometric Model of ConsumptionSpecification of the Econometric Model of Consumption

• The The relationshipsrelationships between economic variables are generally between economic variables are generally inexactinexact. In . In addition to income, other variables affect consumption expenditure. For addition to income, other variables affect consumption expenditure. For example, example, size of family, ages of the members in the family, family religionsize of family, ages of the members in the family, family religion , , etc., are likely to exert some influence on consumption.etc., are likely to exert some influence on consumption.

• To allow for the To allow for the inexactinexact relationships between economic variables, (I.3.1) is relationships between economic variables, (I.3.1) is modified as follows:modified as follows:

• Y = βY = β11 + β + β22X + X + uu (I.3.2)(I.3.2)

• where u, known as where u, known as the disturbance, or error, termthe disturbance, or error, term, , is a random (is a random (stochasticstochastic) ) variable that has well-defined variable that has well-defined probabilistic propertiesprobabilistic properties. The disturbance term . The disturbance term u may well represent all those factors that affect consumption but are not u may well represent all those factors that affect consumption but are not taken into account taken into account explicitly.explicitly.

• (I.3.2) is an example of a linear regression model, i.e., it hypothesizes that (I.3.2) is an example of a linear regression model, i.e., it hypothesizes that Y Y is linearly related to Xis linearly related to X, but that the relationship between the two is, but that the relationship between the two is not exact not exact; ; it is subject to individual variation. The econometric model of (I.3.2) can be it is subject to individual variation. The econometric model of (I.3.2) can be depicted as shown in Figure I.2.depicted as shown in Figure I.2.

4. Obtaining Data4. Obtaining Data

• To obtain the numerical values of To obtain the numerical values of β1 and β2, we need data. β1 and β2, we need data. Look at Table Look at Table I.1, which relate to the I.1, which relate to the personal consumption expenditure personal consumption expenditure (PCE) and the (PCE) and the gross domestic product (GDP)gross domestic product (GDP). The data are in “real” terms.. The data are in “real” terms.

The data are plotted in Figure I.3

5. Estimation of the Econometric Model5. Estimation of the Econometric Model

• Regression analysis Regression analysis is the main tool used to obtain the estimates. Using this is the main tool used to obtain the estimates. Using this technique and the data given in Table I.1, we obtain the following estimates technique and the data given in Table I.1, we obtain the following estimates of of ββ11 and and ββ22, namely, , namely, −184.08 −184.08 and and 0.70640.7064. . Thus, the estimated consumption Thus, the estimated consumption

function is: function is:

• Yˆ = −184.08 + 0.7064XYˆ = −184.08 + 0.7064Xii (I.3.3) (I.3.3)

• The estimated The estimated regression line is shown in Figure I.3. The regression line is shown in Figure I.3. The regression line fits regression line fits the data quite well. The the data quite well. The slopeslope coefficient (i.e., the MPC) was about coefficient (i.e., the MPC) was about 0.70, 0.70, an an increase in real income of 1 dollar led, increase in real income of 1 dollar led, on average, to an increase of about 70 on average, to an increase of about 70 cents in real consumptioncents in real consumption. .

6. Hypothesis Testing6. Hypothesis Testing• That is to find out whether the estimates obtained in, Eq. (I.3.3) are in That is to find out whether the estimates obtained in, Eq. (I.3.3) are in

accord accord with the expectations of the theory that is being testedwith the expectations of the theory that is being tested . Keynes . Keynes expected the expected the MPC to be positive but less than 1MPC to be positive but less than 1. In our example we found the . In our example we found the MPC to be about MPC to be about 0.70. 0.70. But before we accept this finding as confirmation of But before we accept this finding as confirmation of Keynesian consumption theory, we must enquire whether this estimate is Keynesian consumption theory, we must enquire whether this estimate is sufficiently below unity. In other words, is sufficiently below unity. In other words, is 0.70 statistically less than 1? 0.70 statistically less than 1? If it If it is, it may support is, it may support Keynes’ theory.Keynes’ theory.

• Such confirmation or refutation of economic theories on the basis of sample Such confirmation or refutation of economic theories on the basis of sample evidence is based on a branch of statistical theory known as evidence is based on a branch of statistical theory known as statistical statistical inference (hypothesis testing). inference (hypothesis testing).

7. Forecasting or Prediction7. Forecasting or Prediction• To illustrate, suppose we want to predict the mean consumption To illustrate, suppose we want to predict the mean consumption

expenditure for 1997. The GDP value for 1997 was expenditure for 1997. The GDP value for 1997 was 7269.87269.8 billion dollars billion dollars consumption would be:consumption would be:

Yˆ1997 = −184.0779 + 0.7064 (7269.8) Yˆ1997 = −184.0779 + 0.7064 (7269.8) = 4951= 4951.3 .3 (I.3.4)(I.3.4)

• The The actual value actual value of the consumption expenditure reportedof the consumption expenditure reported in 1997 was in 1997 was 4913.5 4913.5 billion dollars. The estimated model (I.3.3) thus billion dollars. The estimated model (I.3.3) thus over-predictedover-predicted the the actual consumption expenditure by about actual consumption expenditure by about 37.8237.82 billion dollars. We could billion dollars. We could say the say the forecast error forecast error is about is about 37.837.8 billion dollars, which is about billion dollars, which is about 0.760.76 percent of the actual GDP value for 1997. percent of the actual GDP value for 1997.

• Now suppose the government decides to propose a Now suppose the government decides to propose a reduction in the income reduction in the income taxtax. What will be the effect of such a policy on income and thereby on . What will be the effect of such a policy on income and thereby on consumption expenditure and ultimately on employment?consumption expenditure and ultimately on employment?

• Suppose that, as a result of the proposed policy change, investment Suppose that, as a result of the proposed policy change, investment expenditure increasesexpenditure increases. What will be the effect on the economy? As . What will be the effect on the economy? As macroeconomic theory shows, the change in income following, a dollar’s macroeconomic theory shows, the change in income following, a dollar’s worth of change in investment expenditure is given by the income worth of change in investment expenditure is given by the income multiplier multiplier M, M, which is defined as:which is defined as:

• M = M = 1/(1 − MPC)1/(1 − MPC) (I.3.5)(I.3.5)

• The multiplier is about The multiplier is about M = 3.33M = 3.33. That is, an increase (decrease) of a dollar . That is, an increase (decrease) of a dollar in investment will eventually in investment will eventually lead to more than a threefold increase lead to more than a threefold increase (decrease) in income; note that it takes time for the multiplier to work.(decrease) in income; note that it takes time for the multiplier to work.

• The critical value in this computation is The critical value in this computation is MPCMPC. Thus, a quantitative estimate . Thus, a quantitative estimate of MPC provides valuable information of MPC provides valuable information for policy purposes. for policy purposes. Knowing MPC, Knowing MPC, one can predict the future course of income, consumption expenditure, and one can predict the future course of income, consumption expenditure, and employment employment following a change in the government’s fiscal policies.following a change in the government’s fiscal policies.

8. Use of the Model for Control or Policy Purposes8. Use of the Model for Control or Policy Purposes• Suppose we have the estimated consumption function given in (I.3.3). Suppose we have the estimated consumption function given in (I.3.3).

Suppose further the government believes that consumer expenditure of Suppose further the government believes that consumer expenditure of about about 49004900 will keep the will keep the unemployment rate at its current level of about unemployment rate at its current level of about 4.2%4.2%. What level of income will guarantee the target amount of . What level of income will guarantee the target amount of consumption expenditure?consumption expenditure?

• If the regression results given in (I.3.3) seem reasonable, simple arithmetic If the regression results given in (I.3.3) seem reasonable, simple arithmetic will show that:will show that:

• 4900 = −1844900 = −184.0779 + 0.7064X .0779 + 0.7064X (I.3.6)(I.3.6)

• which gives which gives X = 7197X = 7197, approximately. That is, an income level of about , approximately. That is, an income level of about 7197 7197 (billion) dollars, given an MPC of about 0.70, will produce an expenditure (billion) dollars, given an MPC of about 0.70, will produce an expenditure of about 4900 billion dollars. As these calculations suggest, an estimated of about 4900 billion dollars. As these calculations suggest, an estimated model may be used for control, or policy, purposes. By appropriate fiscal model may be used for control, or policy, purposes. By appropriate fiscal and monetary policy mix, the government can manipulate the and monetary policy mix, the government can manipulate the control control variable X to produce the desired level of the target variable variable X to produce the desired level of the target variable Y.Y.

• Figure I.4 summarizes the anatomy of classical econometric modeling.Figure I.4 summarizes the anatomy of classical econometric modeling.

• Choosing among Competing ModelsChoosing among Competing Models• When a governmental agency (e.g., the U.S. Department of Commerce) When a governmental agency (e.g., the U.S. Department of Commerce)

collects economic data, such as that shown in Table I.1, it does not collects economic data, such as that shown in Table I.1, it does not necessarily have any economic theory in mindnecessarily have any economic theory in mind . How then does one know that . How then does one know that the data really support the the data really support the KeynesianKeynesian theory of consumption? Is it because theory of consumption? Is it because the Keynesian consumption function (i.e., the regression line) shown in the Keynesian consumption function (i.e., the regression line) shown in Figure I.3 is extremely close to the actual data points? Is it possible that Figure I.3 is extremely close to the actual data points? Is it possible that another consumption another consumption model (theory) might equally fit the data as well? For model (theory) might equally fit the data as well? For example, Milton example, Milton FriedmanFriedman has developed a model of consumption, called has developed a model of consumption, called the the permanent income hypothesispermanent income hypothesis. Robert . Robert HallHall has also developed a model of has also developed a model of consumption, called the consumption, called the life-cycle permanent income hypothesislife-cycle permanent income hypothesis. Could one . Could one or both of these models also fit the data in Table I.1?or both of these models also fit the data in Table I.1?

• In short, the question facing a In short, the question facing a researcherresearcher in practice is in practice is how to choose how to choose among competing hypotheses or models of a given phenomenon, such as the among competing hypotheses or models of a given phenomenon, such as the consumption–income relationship.consumption–income relationship.

• The eight-step classical econometric methodology discussed above isThe eight-step classical econometric methodology discussed above is neutral neutral in the sense that it can be used to test any of these rival hypothesesin the sense that it can be used to test any of these rival hypotheses. Is it . Is it possible to develop a methodology that is comprehensive enough to include possible to develop a methodology that is comprehensive enough to include competing hypotheses? This is an involved and controversial topic.competing hypotheses? This is an involved and controversial topic.