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1、Chapter 19,Carrying Out an Empirical Project,Wooldridge: Introductory Econometrics: A Modern Approach, 5e,Goal of this chapter Learn how to complete a term project/write a term paper Posing a question Knowing precisely what question you want to answer is essential You can only collect your data if y
2、ou exactly know your question You can only know whether you can complete your project in the allotted time if you know whether the necessary data is available You can only know if your research question is of interest to someone if you can precisely state it and discuss it with your class mates/inst
3、ructor,Carrying out an Empirical Project,Finding interesting research questions Choose the area of economics/social sciences you are interested in Examples for typical research questions Labor Economics: Explaining wage differentials Public Economics: Effect of taxes on economic activity Education E
4、conomics: Effect of spending on school performance Macroeconomics: Effect of investment on GNP growth Look for published papers on the chosen topic using tools such as EconLit, Google Scholar, the Journal of Economic Literature (JEL) etc.,Carrying out an Empirical Project,Your research project shoul
5、d add something new Add a new variable whose influence has not been studied before Expand economic questions to include factors from other sciences Study an existing question for more recent data (may be boring) Use a new data set or study a question for a different country Try out new/alternative m
6、ethods to study an old question Find a completely new question (hard but possible) It helps if your research question is policy relevant or of local interest,Carrying out an Empirical Project,Literature review A literature review is important to place your paper into context Use online search servic
7、es to systematically search for literature When searching, think of related topics that may also be relevant A literature review can be part of introduction or a separate section Data collection Most questions can be addressed using alternative types of data (pure cross-sections, repeated cross-sect
8、ions, time series, panels),Carrying out an Empirical Project,Deciding on the appropriate data set Many questions can in principle be studied using a single cross-section But for a reasonable ceteris paribus analysis one needs enough controls Panel data provides more possibilities for convincing cete
9、ris paribus analyses as one can control for time-invariant unobserved effects Examples for panel data sets: PSID (individuals), Compustat (firms) Panel data for cities, counties, states etc. are often publicly available Data sets are often available online, in journal archives, or from authors,Carry
10、ing out an Empirical Project,Entering and storing your data Data formats: 1) printed, 2) ASCII, 3) spreadsheet, 4) software specific Important identifiers: 1) observational unit, 2) time period Time series must be ordered according to time period Panel data are conveniently ordered as blocks of indi
11、vidual data It is always important to correctly identify and handle missing values Nonnummerical data also have to be handled with great care Software specific formats often provide good ways of documentation,Carrying out an Empirical Project,Inspecting, cleaning, and summarizing your data It is ext
12、remely important to become familiar with your data set Even data sets that were used before may contain problems/errors Look at individual entries/try to understand the structure of your data Understand how missing values are coded; if they are coded as “999“ or “-1“, this can be extremely dangerous
13、 for your analysis It is better to use nonnummerical values for missing values Understand the units of measurement of your variables,Carrying out an Empirical Project,Inspecting, cleaning, and summarizing your data Know whether your data is real/nominal, seasonally adjusted/unadjusted Check if means
14、, std.dev., mins, and maxs of your data are plausible Clean your data of implausible values and obvious coding errors When making data transformations (differencing, growth rates) make sure your data is correctly ordered and no wrong operations result For example, in a panel data set, be aware that
15、the first observation of each cross-sectional unit has no predecessor,Carrying out an Empirical Project,Econometric Analysis Given your research question and the data available, you have to decide on the appropriate econometric methods to use Some general guidelines OLS is still the most widely used
16、 method and often appropriate Make sure the key assumptions are satisfied in your model Always check for possible problems of omitted variables, self-selection, measurement error, and simultaneity,Carrying out an Empirical Project,Some general guidelines Carefully choose functional form specifications (logs, squares etc.) Beginners mistake: do not include variables that are listed as numerical values but have no quantitative meaning (e.g., 3-digit occupations) Transform such varia
