Hi all,
For my master thesis, I am looking at the effect of cross-listing on a firm's leverage ratio. I have formed a treatment group (=cross-listed firms) and a control group (=non-cross-listed firms), based on supposedly similar characteristics such as firm size, market-to-book ratio, and cost of capital. Due to lack of data for numerous observations, I have unbalanced panel data. I am a novice Stata user and not very experienced with statistics in general.
I have run a difference-in-differences analysis, where the time dummy comprises the 5 years prior to (=0) and 5 years after (=1) the treatment:
I notice that the outcome is rather puzzling: a pre-treatment statistical difference in leverage ratios between treated and control group, and a smaller and insignificant difference post-treatment.
When I change the time period to only look at the two years before and after the treatment, the outcome seems to be slightly more satisfying, but not yet usable for my research:
Ideally, I want to find no statistical differences in leverage pre-treatment, and a statistical difference (I suspect the cross-listing to have a negative effect on leverage ratio) post-treatment.
Can an explanation for the lack of desired outcome be the difference in numbers of observations between the pre- and post-treatment period?
I have read that differences between size of control and treatment group should not matter, but I have never read about pre- and post-treatment differences.
Thanks!
Oscar
For my master thesis, I am looking at the effect of cross-listing on a firm's leverage ratio. I have formed a treatment group (=cross-listed firms) and a control group (=non-cross-listed firms), based on supposedly similar characteristics such as firm size, market-to-book ratio, and cost of capital. Due to lack of data for numerous observations, I have unbalanced panel data. I am a novice Stata user and not very experienced with statistics in general.
I have run a difference-in-differences analysis, where the time dummy comprises the 5 years prior to (=0) and 5 years after (=1) the treatment:
Code:
. diff lvg, t(d_cl) p(d_time5) DIFFERENCE-IN-DIFFERENCES ESTIMATION RESULTS Number of observations in the DIFF-IN-DIFF: 2967 Baseline Follow-up Control: 673 1020 1693 Treated: 574 700 1274 1247 1720 ------------------------------------------------------ Outcome var. | lvg | S. Err. | t | P>|t| ----------------+---------+---------+-------+--------- Baseline | | | | Control | 0.214 | | | Treated | 0.235 | | | Diff (T-C) | 0.022 | 0.011 | 2.01 | 0.045** Follow-up | | | | Control | 0.204 | | | Treated | 0.216 | | | Diff (T-C) | 0.012 | 0.009 | 1.31 | 0.191 | | | | Diff-in-Diff | -0.009 | 0.014 | -0.66 | 0.508 ------------------------------------------------------ R-square: 0.00 - Means and Standard Errors are estimated by linear regression **Inference: *** p<0.01; ** p<0.05; * p<0.1
When I change the time period to only look at the two years before and after the treatment, the outcome seems to be slightly more satisfying, but not yet usable for my research:
Code:
. diff lvg, t(d_cl) p(d_time2) DIFFERENCE-IN-DIFFERENCES ESTIMATION RESULTS Number of observations in the DIFF-IN-DIFF: 1461 Baseline Follow-up Control: 371 455 826 Treated: 308 327 635 679 782 ------------------------------------------------------ Outcome var. | lvg | S. Err. | t | P>|t| ----------------+---------+---------+-------+--------- Baseline | | | | Control | 0.205 | | | Treated | 0.230 | | | Diff (T-C) | 0.025 | 0.015 | 1.66 | 0.098* Follow-up | | | | Control | 0.215 | | | Treated | 0.209 | | | Diff (T-C) | -0.006 | 0.014 | -0.42 | 0.673 | | | | Diff-in-Diff | -0.031 | 0.021 | -1.49 | 0.135 ------------------------------------------------------ R-square: 0.00 - Means and Standard Errors are estimated by linear regression **Inference: *** p<0.01; ** p<0.05; * p<0.1
Can an explanation for the lack of desired outcome be the difference in numbers of observations between the pre- and post-treatment period?
I have read that differences between size of control and treatment group should not matter, but I have never read about pre- and post-treatment differences.
Thanks!
Oscar
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