Dear Stata members,
I am running Interrupted Time Series on my data set. My question is that, when I run ITS with my covariates and plot the post trend figure, the figure does not represent the coefficients (slopes) I obtained in the regression.
If you look at the code and the figure bellow, you can see that in the regression, the slope after the intervention is negative while in the figure the slope after the intervention is positive. The figure seems to represent the ITS result without any covariates. So could anyone please explain me how can I interpret this?
I am running Interrupted Time Series on my data set. My question is that, when I run ITS with my covariates and plot the post trend figure, the figure does not represent the coefficients (slopes) I obtained in the regression.
If you look at the code and the figure bellow, you can see that in the regression, the slope after the intervention is negative while in the figure the slope after the intervention is positive. The figure seems to represent the ITS result without any covariates. So could anyone please explain me how can I interpret this?
Code:
. xtset pannel_var weeks_from_start
Panel variable: pannel_var (unbalanced)
Time variable: weeks_from_start, -36 to 16, but with gaps
Delta: 1 unit
.
. xtitsa positivity_rate if weeks_from_start < 14 & weeks_from_start > -10, single trperiod(0) posttrend figure replace
Panel variable: pannel_var (unbalanced)
Time variable: weeks_from_start, -36 to 16, but with gaps
Delta: 1 unit
------------------------------------------------------------------------------
_positivit~e | Coefficient Std. err. z P>|z| [95% conf. interval]
-------------+----------------------------------------------------------------
_t | -.0023408 .0002131 -10.99 0.000 -.0027585 -.0019232
_x0 | -.0395572 .0024548 -16.11 0.000 -.0443685 -.0347459
_x_t0 | .0043239 .0003358 12.88 0.000 .0036658 .004982
_cons | .068182 .0013013 52.40 0.000 .0656315 .0707325
------------------------------------------------------------------------------
Postintervention Linear Trend: 0
Treated: _b[_t]+_b[_x_t0]
------------------------------------------------------------------------------
Linear Trend | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
Treated | .0019831 .0002735 7.25 0.000 .001447 .0025192
------------------------------------------------------------------------------
. xtitsa positivity_rate i.weeks_from_start_pos i._x0#c.cases_norm i._x0#c.full_district_porportion i._x0#c.consent_rate_cumsum i._x0#c.black i._x0#c.white i._x0#c.hispanic i._x0#c.other i._x0#i.rural i._x0#i.title1 i._x0#i.charter i._x0#i.surv_group i._x0#i.masking_policy i._x0#i.school_category if weeks_from_start < 14 & weeks_from_start > -10, sngle trperiod(0) posttrend figure replace
Panel variable: pannel_var (unbalanced)
Time variable: weeks_from_start, -36 to 16, but with gaps
Delta: 1 unit
------------------------------------------------------------------------------------------------
_positivity_rate | Coefficient Std. err. z P>|z| [95% conf. interval]
-------------------------------+----------------------------------------------------------------
_t | -.0001731 .0001633 -1.06 0.289 -.0004931 .0001469
_x0 | -.1342962 .0185167 -7.25 0.000 -.1705883 -.0980041
_x_t0 | -.004014 .0013141 -3.05 0.002 -.0065896 -.0014385
|
weeks_from_start_pos |
30 | -.0523541 .0020964 -24.97 0.000 -.056463 -.0482451
32 | -.0853062 .0023276 -36.65 0.000 -.0898681 -.0807442
34 | -.0953261 .0026281 -36.27 0.000 -.100477 -.0901752
36 | -.0704673 .0143642 -4.91 0.000 -.0986207 -.042314
38 | -.0579889 .0117729 -4.93 0.000 -.0810633 -.0349145
40 | -.0447715 .0092084 -4.86 0.000 -.0628197 -.0267233
42 | -.0315088 .0067481 -4.67 0.000 -.0447348 -.0182828
44 | -.0158642 .0043358 -3.66 0.000 -.0243621 -.0073662
46 | 0 (omitted)
48 | 0 (omitted)
|
_x0#c.cases_norm |
0 | -.3758737 .0258557 -14.54 0.000 -.42655 -.3251973
1 | -.0242011 .0267325 -0.91 0.365 -.0765958 .0281937
|
_x0#c.full_district_porportion |
0 | -.0519608 .0071885 -7.23 0.000 -.0660501 -.0378715
1 | -.0078668 .0071432 -1.10 0.271 -.0218671 .0061336
|
_x0#c.consent_rate_cumsum |
0 | -.0254564 .00303 -8.40 0.000 -.0313951 -.0195176
1 | -.0026842 .0028657 -0.94 0.349 -.0083008 .0029324
|
_x0#c.black |
0 | -.0001852 .0000719 -2.57 0.010 -.0003262 -.0000442
1 | .0001368 .0000717 1.91 0.057 -3.84e-06 .0002773
|
_x0#c.white |
0 | -.0000706 .0000371 -1.90 0.057 -.0001432 2.07e-06
1 | -1.80e-06 .0000334 -0.05 0.957 -.0000674 .0000638
|
_x0#c.hispanic |
0 | -.0000465 .0000535 -0.87 0.385 -.0001514 .0000585
1 | -.0000212 .0000564 -0.38 0.707 -.0001317 .0000893
|
_x0#c.other |
0 | -.0001777 .0000615 -2.89 0.004 -.0002982 -.0000572
1 | -.0000154 .0000537 -0.29 0.775 -.0001207 .00009
|
_x0#rural |
0 1 | -.0369213 .0055236 -6.68 0.000 -.0477473 -.0260953
1 0 | -.0031388 .005203 -0.60 0.546 -.0133366 .007059
1 1 | 0 (omitted)
|
_x0#title1 |
0 1 | -.0235955 .0035583 -6.63 0.000 -.0305696 -.0166214
1 0 | .0058005 .0034026 1.70 0.088 -.0008684 .0124694
1 1 | 0 (omitted)
|
_x0#charter |
0 1 | .0108525 .0043938 2.47 0.014 .0022409 .0194641
1 0 | -.0018951 .0042701 -0.44 0.657 -.0102644 .0064742
1 1 | 0 (omitted)
|
_x0#surv_group |
0 1 | 0 (omitted)
1 1 | 0 (omitted)
|
_x0#masking_policy |
0 0 | 0 (empty)
0 1 | 0 (omitted)
1 0 | -.0118502 .0033287 -3.56 0.000 -.0183743 -.0053262
1 1 | 0 (omitted)
|
_x0#school_category |
0#public | .0162698 .0024816 6.56 0.000 .0114059 .0211337
1#private | -.0005974 .0022571 -0.26 0.791 -.0050213 .0038264
1#public | 0 (omitted)
|
_cons | .2424306 .0079723 30.41 0.000 .2268053 .2580559
------------------------------------------------------------------------------------------------
Postintervention Linear Trend: 0
Treated: _b[_t]+_b[_x_t0]
------------------------------------------------------------------------------
Linear Trend | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
Treated | -.0041872 .0012989 -3.22 0.001 -.006733 -.0016414
------------------------------------------------------------------------------
.
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