### T-test of unit price, for all medicines together ### fta_inforce = 1 if a country has obligations with US in the year of observation; = 0 otherwise . ttest unitpriceexworks if originatorgeneric=="originator", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 20900 .4940421 .0111723 1.615162 .4721436 .5159407 1 | 651 1.136246 .0674019 1.719739 1.003894 1.268598 ---------+-------------------------------------------------------------------- combined | 21551 .5134415 .0110496 1.622107 .4917835 .5350995 ---------+-------------------------------------------------------------------- diff | -.6422039 .064411 -.7684543 -.5159535 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -9.9704 Ho: diff = 0 degrees of freedom = 21549 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 ### T-tests for each drug with over 1000 observations in the dataset . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Abacavir [ABC]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 1138 .4938183 .0153241 .516946 .4637516 .5238849 1 | 19 .6802393 .1444434 .6296141 .376775 .9837036 ---------+-------------------------------------------------------------------- combined | 1157 .4968796 .0152642 .5192064 .466931 .5268282 ---------+-------------------------------------------------------------------- diff | -.186421 .1200311 -.4219244 .0490824 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -1.5531 Ho: diff = 0 degrees of freedom = 1155 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0603 Pr(|T| > |t|) = 0.1207 Pr(T > t) = 0.9397 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Didanosine [ddI]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 2731 .5922186 .0141117 .7374636 .5645479 .6198893 1 | 77 1.71135 .1711661 1.501976 1.370443 2.052256 ---------+-------------------------------------------------------------------- combined | 2808 .622907 .0149003 .7895747 .5936904 .6521236 ---------+-------------------------------------------------------------------- diff | -1.119131 .0887771 -1.293206 -.945056 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -12.6061 Ho: diff = 0 degrees of freedom = 2806 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Efavirenz [EFV]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 2234 .4163119 .0079137 .374042 .400793 .4318309 1 | 140 .6808184 .0436583 .5165716 .5944983 .7671386 ---------+-------------------------------------------------------------------- combined | 2374 .4319104 .0079798 .3888036 .4162624 .4475585 ---------+-------------------------------------------------------------------- diff | -.2645065 .0334429 -.3300869 -.1989262 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -7.9092 Ho: diff = 0 degrees of freedom = 2372 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Lamivudine [3TC]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 1336 .1120308 .005731 .2094766 .100788 .1232736 1 | 32 .2232935 .092375 .522552 .0348934 .4116936 ---------+-------------------------------------------------------------------- combined | 1368 .1146335 .0060049 .2221004 .1028536 .1264133 ---------+-------------------------------------------------------------------- diff | -.1112627 .03963 -.1890048 -.0335205 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -2.8075 Ho: diff = 0 degrees of freedom = 1366 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0025 Pr(|T| > |t|) = 0.0051 Pr(T > t) = 0.9975 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Lopinavir + Ritonavir [LPV+RTV]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 5385 .2790058 .0039249 .2880162 .2713115 .2867001 1 | 181 .4896115 .0253057 .3404529 .4396776 .5395454 ---------+-------------------------------------------------------------------- combined | 5566 .2858544 .003917 .2922329 .2781755 .2935334 ---------+-------------------------------------------------------------------- diff | -.2106057 .0219043 -.2535467 -.1676647 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -9.6148 Ho: diff = 0 degrees of freedom = 5564 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Nevirapine [NVP]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 620 .2168607 .0086554 .2155186 .1998631 .2338582 1 | 3 .3263196 .2908027 .503685 -.9249034 1.577543 ---------+-------------------------------------------------------------------- combined | 623 .2173877 .0086947 .2170196 .2003132 .2344623 ---------+-------------------------------------------------------------------- diff | -.1094589 .1256234 -.3561571 .1372393 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -0.8713 Ho: diff = 0 degrees of freedom = 621 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.1920 Pr(|T| > |t|) = 0.3839 Pr(T > t) = 0.8080 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Stavudine [d4T]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 1527 .069738 .0010596 .041406 .0676595 .0718164 1 | 4 .0167538 .0014642 .0029284 .012094 .0214136 ---------+-------------------------------------------------------------------- combined | 1531 .0695995 .0010591 .0414405 .0675221 .071677 ---------+-------------------------------------------------------------------- diff | .0529841 .0207099 .0123614 .0936069 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = 2.5584 Ho: diff = 0 degrees of freedom = 1529 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.9947 Pr(|T| > |t|) = 0.0106 Pr(T > t) = 0.0053 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Zidovudine + Lamivudine [ZDV+3TC]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 634 .347292 .0085442 .2151364 .3305136 .3640703 1 | 21 .6812607 .1329947 .6094583 .4038386 .9586827 ---------+-------------------------------------------------------------------- combined | 655 .3579994 .0095408 .2441784 .339265 .3767337 ---------+-------------------------------------------------------------------- diff | -.3339687 .0526016 -.4372573 -.2306801 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -6.3490 Ho: diff = 0 degrees of freedom = 653 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 . ttest unitpriceexworks if originatorgeneric=="originator" & inname=="Zidovudine [ZDV]", by(fta_inforce) Two-sample t test with equal variances ------------------------------------------------------------------------------ Group | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------------- 0 | 1063 .5892172 .0514891 1.678734 .4881853 .6902492 1 | 26 4.788833 .6895558 3.516059 3.368667 6.209 ---------+-------------------------------------------------------------------- combined | 1089 .6894835 .056255 1.856415 .579103 .7998641 ---------+-------------------------------------------------------------------- diff | -4.199616 .3459637 -4.878448 -3.520784 ------------------------------------------------------------------------------ diff = mean(0) - mean(1) t = -12.1389 Ho: diff = 0 degrees of freedom = 1087 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 Pr(T < t) = 0.0000 Pr(|T| > |t|) = 0.0000 Pr(T > t) = 1.0000 ### Create "ARV" dummy variables for use in Dummy Variables Least Squares . encode inname, generate(arv) ### Dummy Variables Least Squares Regression . areg unitpriceexworks fta_inforce log_gnipc who year if originatorgeneric=="originator", absorb(arv) robust Linear regression, absorbing indicators Number of obs = 20472 F( 4, 20440) = 88.48 Prob > F = 0.0000 R-squared = 0.7697 Adj R-squared = 0.7693 Root MSE = 0.7695 ------------------------------------------------------------------------------ | Robust unitpricee~s | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- fta_inforce | .5744077 .0588765 9.76 0.000 .4590051 .6898103 log_gnipc | .0550481 .0042939 12.82 0.000 .0466316 .0634646 who | -.0774002 .0193736 -4.00 0.000 -.115374 -.0394264 year | -.0338265 .0030953 -10.93 0.000 -.0398936 -.0277595 _cons | 68.06937 6.200784 10.98 0.000 55.91533 80.2234 -------------+---------------------------------------------------------------- arv | absorbed (28 categories) ### Dummy Variables Least Squares Regression with WHO dropped . areg unitpriceexworks fta_inforce log_gnipc year if originatorgeneric=="originator", absorb(arv) robust Linear regression, absorbing indicators Number of obs = 20472 F( 3, 20441) = 115.09 Prob > F = 0.0000 R-squared = 0.7695 Adj R-squared = 0.7692 Root MSE = 0.7697 ------------------------------------------------------------------------------ | Robust unitpricee~s | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- fta_inforce | .5736934 .0589033 9.74 0.000 .4582381 .6891486 log_gnipc | .0559874 .0042645 13.13 0.000 .0476288 .0643461 year | -.0319703 .0030215 -10.58 0.000 -.0378927 -.0260479 _cons | 64.27038 6.047587 10.63 0.000 52.41663 76.12414 -------------+---------------------------------------------------------------- arv | absorbed (28 categories) ### OLS regression with dummy variables for ARVs dropped . reg unitpriceexworks fta_inforce log_gnipc who year if originatorgeneric=="originator", robust Linear regression Number of obs = 20472 F( 4, 20467) = 69.20 Prob > F = 0.0000 R-squared = 0.0326 Root MSE = 1.576 ------------------------------------------------------------------------------ | Robust unitpricee~s | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- fta_inforce | .6248474 .0667939 9.35 0.000 .4939261 .7557687 log_gnipc | .0685764 .0070518 9.72 0.000 .0547542 .0823985 who | -.6626237 .0572999 -11.56 0.000 -.7749361 -.5503114 year | -.0090449 .0040596 -2.23 0.026 -.0170021 -.0010877 _cons | 18.67534 8.130024 2.30 0.022 2.739841 34.61083 ------------------------------------------------------------------------------