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  • Insignificant F statistics, R square approximately equal to 0. Insignficant t statistics

    Dear Stata list members

    Advance apologies for asking a naive question. I conducted an analysis to check whether firm-level working capital prior to the COVID-19 crisis(i.e. working capital level ex-ante crisis) is associated with the stock performance during the crisis period(crisis period, for instance, 1st quarter of the year 2020). My idea was motivated by recent media reports and anecdotes citing that firms will be facing a low demand hence those firms with excess inventory, more receivables (inventory, receivables and payables etc are the constituents of working capital) will be hard hit by the outbreak of COVID-19 (alternative logic says excess inventories will be good for during crisis times). Of course, the working capital level will be changing but still, there will be firms which may have stocked more inventories vis-à-vis with their peers. How do market value such firms during the crisis time based on their working capital measured before the crisis. To operationalize this, I ran an OLS with the dependent variable, “return” measured as Log of (Price at 31/03/2020/ Price at 01/01/2020), and following independent variables,- inventory scaled by total assets accounts receivables scaled by total assets, accounts payables scaled by total assets, cash holdings scaled by total assets, Ln(total assets) and industry dummies. All the independent variables are measured as of 2019 March.
    Thus, I have a cross-sectional data where each firm will have one observation as dependent variable(returns) with independent variables
    Code:
    Log returns for each firm=Constant+ Beta*receivables of each firm + Beta*payables of each firm……+Beta*ln(total asssets) + Industry dummies
    Results: I ran the above regressions and I got a poor model (by F value and adjusted R^2) in which none of the coefficients was significant.
    I repeatedly did this with different returns considering the different period and none worked.
    I have read that if none of the independent variables are statistically significant, the overall F-test is also not statistically significant. Also, F stat is a joint test which tests whether the linear regression model provides a better fit to the data than a model that contains no independent variables. This was true since my intercept was having a higher magnitude and was statistically significant
    Before giving up this idea, I have a few doubts
    1. Why even known predictors of stock returns like Log(total assets) didn’t show significance?
    2. Was my model a wrong one (using OLS, wrong measure of returns etc) even though same models got results in many working papers
    3. Market reaction has nothing to do with my independent variables (as my F statistics indicated)

  • #2
    Ial:
    I fail to get why you devoted so many words in trying to descibe accurately what you experienced but omitted to share what you typed and what Stata gave you back (as recommended by the FAQ and reminded many times on this forum).
    Kind regards,
    Carlo
    (Stata 19.0)

    Comment


    • #3
      Dear Carlo
      I am extremely sorry for not sharing my inputs and outputs.

      I ran the following commands
      Code:
      reg log_ret_w size_w leverage_w  inv_ta_w rece_ta_w payacc_ta_w   cashincstin_ta_w
      The results I got is tabulated below
      No : of observations 249
      Source SS df MS F(6,242) 1.46
      Model 0.39956 6 0.06559 Prob>F 0.1934
      Residual 11.0545 242 0.04567 R-squared 0.0349
      Adj R-squared 0.011
      Root MSE 0.21373
      log_ret_w Coef. Std. Err. t P>t [95% Conf. Interval]
      size_w 0.017227 0.007199 2.39 0.017 0.003047 0.031407
      leverage_w -0.00433 0.0256 -0.17 0.866 -0.0547532 0.046103
      inv_ta_w -0.01911 0.085283 -0.22 0.823 -0.1871007 0.148881
      rece_ta_w 0.07101 0.098616 0.72 0.472 -0.123246 0.265266
      payacc_ta_w 0.053251 0.107762 0.49 0.622 -0.15902 0.265521
      cashincstin_ta_w 0.234074 0.187456 1.25 0.213 -0.1351794 0.603327
      _cons -0.47232 0.075389 -6.27 0 -0.6208274 -0.32382
      Where size, leverage, inv_ta_w etc are my independent variables, log_ret_w is my dependent variable. I winsorized all these variables

      Later I modified the code to include Industry dummies also

      Code:
      reg log_ret_w size_w leverage_w  inv_ta_w rece_ta_w payacc_ta_w   cashincstin_ta_w i.industry
      When I put the cluster option, F stats were missing
      Code:
      reg log_ret_w size_w leverage_w  net_trade_debt_w cashban_ta_w i.industry,vce(cluster industry)
      I am extremely sorry for the inadvertent mistakes while posting
      Last edited by lal mohan kumar; 08 Jul 2020, 10:10.

      Comment


      • #4
        Ial:
        you can use CODE delimiters to post Stata codes (as you did) and Stata outcome tables (as you did not).
        That said:
        1) it may well be that your preditcors have no effect on the regressand. It's difficult to say whether no effect exist in the population from which your sample was drawn or the absence of evidence is not evidence of absence (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC351831/), but only a consequence of your limited sample size,
        2) as far as the missing F-test statistics is concerned, see -help j_robustsingular-.
        Kind regards,
        Carlo
        (Stata 19.0)

        Comment


        • #5
          Thanks, Carlo. Though I tried using bigger sample size, (>3000- using entire listed companies in the stock exchange), results were the same(insignificant coefficients). As you suggested, my predictors may not have an effect on the dependent variables could be the reason(though theoretically relationship is justified). Thanks Carlo once again

          Comment


          • #6
            Ial.
            It may also be that you omitted some relvant predictors, giving a limited representation of the data generating process (the R-sq is very low).
            I would skim through the literature of your research field and see if any good recommendation comes alive.
            Kind regards,
            Carlo
            (Stata 19.0)

            Comment


            • #7
              Carlo, it is kind of you to help me. Meanwhile, let me too read further to make the model a better one.

              Comment

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