obtain p50, p25 and p75 and have line graph

[Gabriel Temesgen]

Dears,
I want to obtain p50, p25, and p75 and line a graph with a median with interquartile.

generate qrt = tq(2000q1) + _n-1
format %tq qrt
tsset qrt
order qrt, first
* I use this code to collapse
collapse (p50) mean=by (p25) p25=by (p75) p75=by , by(qrt)
however, the p50, p25 and p75 the same values.
Any help to solve this. How can I get different values of p50, p25 and p75?

* Example generated by -dataex-. To install: ssc install dataex
clear
input float qrt str6 date float by
160 "2000q1"   40
161 "2000q2"   40
162 "2000q3" 39.5
163 "2000q4"   38
164 "2001q1" 36.7
165 "2001q2" 37.2
166 "2001q3" 37.7
167 "2001q4" 38.1
168 "2002q1" 35.9
169 "2002q2"   36
170 "2002q3" 35.1
171 "2002q4" 31.8
172 "2003q1" 30.4
173 "2003q2" 31.1
174 "2003q3" 31.3
175 "2003q4" 31.6
176 "2004q1" 29.8
177 "2004q2" 30.5
178 "2004q3"   31
179 "2004q4" 30.8
180 "2005q1" 29.7
181 "2005q2" 30.5
182 "2005q3"   30
183 "2005q4" 29.6
184 "2006q1"   28
185 "2006q2"   29
186 "2006q3" 29.2
187 "2006q4"   28
188 "2007q1" 25.9
189 "2007q2" 25.3
190 "2007q3" 24.9
191 "2007q4" 24.3
192 "2008q1" 23.7
193 "2008q2" 23.7
194 "2008q3" 23.5
195 "2008q4"   24
196 "2009q1" 23.6
197 "2009q2" 24.8
198 "2009q3"   26
199 "2009q4"   27
200 "2010q1" 28.3
201 "2010q2" 29.7
202 "2010q3" 30.3
203 "2010q4" 31.2
204 "2011q1" 31.9
205 "2011q2" 32.8
206 "2011q3" 33.9
207 "2011q4" 34.7
208 "2012q1"   35
209 "2012q2" 35.9
210 "2012q3" 36.2
211 "2012q4" 37.4
212 "2013q1" 37.6
213 "2013q2" 38.5
214 "2013q3" 39.3
215 "2013q4" 40.4
216 "2014q1" 40.2
217 "2014q2" 40.9
218 "2014q3" 42.3
219 "2014q4" 43.3
220 "2015q1" 42.8
221 "2015q2" 43.3
222 "2015q3" 44.5
223 "2015q4" 45.2
224 "2016q1" 44.9
225 "2016q2" 45.7
226 "2016q3"   46
227 "2016q4" 47.1
228 "2017q1" 46.2
229 "2017q2" 47.2
230 "2017q3" 48.6
231 "2017q4" 48.6
232 "2018q1" 48.5
233 "2018q2" 50.1
234 "2018q3" 51.1
235 "2018q4" 51.5
236 "2019q1" 51.4
237 "2019q2" 52.8
238 "2019q3" 55.5
239 "2019q4" 56.1
240 "2020q1" 57.1
241 "2020q2" 62.2
242 "2020q3" 67.3
243 "2020q4" 68.9
244 "2021q1" 70.1
245 "2021q2" 67.8
246 "2021q3"   68
247 "2021q4" 68.8
248 "2022q1" 67.8
249 "2022q2" 69.8
250 "2022q3" 71.2
251 "2022q4" 71.1
252 "2023q1" 70.9
253 "2023q2" 72.8
254 "2023q3"   74
255 "2023q4" 73.9
end
format %tq qrt

after collapse

* Example generated by -dataex-. To install: ssc install dataex
clear
input float(qrt mean p25 p75)
160   40   40   40
161   40   40   40
162 39.5 39.5 39.5
163   38   38   38
164 36.7 36.7 36.7
165 37.2 37.2 37.2
166 37.7 37.7 37.7
167 38.1 38.1 38.1
168 35.9 35.9 35.9
169   36   36   36
170 35.1 35.1 35.1
171 31.8 31.8 31.8
172 30.4 30.4 30.4
173 31.1 31.1 31.1
174 31.3 31.3 31.3
175 31.6 31.6 31.6
176 29.8 29.8 29.8
177 30.5 30.5 30.5
178   31   31   31
179 30.8 30.8 30.8
180 29.7 29.7 29.7
181 30.5 30.5 30.5
182   30   30   30
183 29.6 29.6 29.6
184   28   28   28
185   29   29   29
186 29.2 29.2 29.2
187   28   28   28
188 25.9 25.9 25.9
189 25.3 25.3 25.3
190 24.9 24.9 24.9
191 24.3 24.3 24.3
192 23.7 23.7 23.7
193 23.7 23.7 23.7
194 23.5 23.5 23.5
195   24   24   24
196 23.6 23.6 23.6
197 24.8 24.8 24.8
198   26   26   26
199   27   27   27
200 28.3 28.3 28.3
201 29.7 29.7 29.7
202 30.3 30.3 30.3
203 31.2 31.2 31.2
204 31.9 31.9 31.9
205 32.8 32.8 32.8
206 33.9 33.9 33.9
207 34.7 34.7 34.7
208   35   35   35
209 35.9 35.9 35.9
210 36.2 36.2 36.2
211 37.4 37.4 37.4
212 37.6 37.6 37.6
213 38.5 38.5 38.5
214 39.3 39.3 39.3
215 40.4 40.4 40.4
216 40.2 40.2 40.2
217 40.9 40.9 40.9
218 42.3 42.3 42.3
219 43.3 43.3 43.3
220 42.8 42.8 42.8
221 43.3 43.3 43.3
222 44.5 44.5 44.5
223 45.2 45.2 45.2
224 44.9 44.9 44.9
225 45.7 45.7 45.7
226   46   46   46
227 47.1 47.1 47.1
228 46.2 46.2 46.2
229 47.2 47.2 47.2
230 48.6 48.6 48.6
231 48.6 48.6 48.6
232 48.5 48.5 48.5
233 50.1 50.1 50.1
234 51.1 51.1 51.1
235 51.5 51.5 51.5
236 51.4 51.4 51.4
237 52.8 52.8 52.8
238 55.5 55.5 55.5
239 56.1 56.1 56.1
240 57.1 57.1 57.1
241 62.2 62.2 62.2
242 67.3 67.3 67.3
243 68.9 68.9 68.9
244 70.1 70.1 70.1
245 67.8 67.8 67.8
246   68   68   68
247 68.8 68.8 68.8
248 67.8 67.8 67.8
249 69.8 69.8 69.8
250 71.2 71.2 71.2
251 71.1 71.1 71.1
252 70.9 70.9 70.9
253 72.8 72.8 72.8
254   74   74   74
255 73.9 73.9 73.9
end
format %tq qrt

[Nick Cox]

In your data example, each quarterly date occurs just once, do that median and quartiles will necessarily be equal.