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Re: st: graph results of bitest stratified with by(var)
From
Michael McCulloch <[email protected]>
To
[email protected]
Subject
Re: st: graph results of bitest stratified with by(var)
Date
Fri, 24 Jan 2014 07:49:14 -0800
Nick, apologies for veering off track.
The -statsby- suggestion works well, indeed with more levels as I've tested below:
sysuse auto.dta, clear
gen group="a" if price<5000
replace group="b" if price>=7000&price<10000
replace group="c" if price>=10000
bitest foreign=.2 if group=="a"
bitest foreign=.2 if group=="b"
statsby, clear by(group): bitest foreign=.2
l group N p, clean noobs
Many thanks.
Best wishes,
Michael McCulloch
--
Pine Street Foundation, since 1989
124 Pine Street | San Anselmo | California | 94960-2674
P: (415) 407-1357 | F: (206) 338-2391 | http://www.PineStreetFoundation.org
On Jan 24, 2014, at 6:20 AM, Nick Cox wrote:
> <>
>
> This is triply mysterious:
>
> 1. You refer to -svret- and -tabout-, but these are user-written
> commands (both from SSC), as you are asked to explain.
>
> 2. On the face of it, -statsby- is a superior solution for saving
> results groupwise, as -svret- saves only the last set of results and
> so it use would necessitate reading your data in again.
>
> 3. It is not correct that -svret- saves only the first values.
> Compare these results, which show that once the loop over groups
> is completed, the results saved are those for the last (second) values
> calculated, as should be expected: each time around the loop, previous
> r-class results are overwritten.
>
> . sysuse auto.dta, clear
> (1978 Automobile Data)
> . gen group=1 if price<5000
> (37 missing values generated)
> . replace group=2 if price>=5000
> (37 real changes made)
> . levelsof group, local(levels)
> 1 2
> . foreach l of local levels {
> 2. bitest foreign=.2 if group == `l'
> 3. }
> Variable | N Observed k Expected k Assumed p Observed p
> -------------+------------------------------------------------------------
> foreign | 37 8 7.4 0.20000 0.21622
> Pr(k >= 8) = 0.467034 (one-sided test)
> Pr(k <= 8) = 0.685908 (one-sided test)
> Pr(k <= 6 or k >= 8) = 0.836862 (two-sided test)
> Variable | N Observed k Expected k Assumed p Observed p
> -------------+------------------------------------------------------------
> foreign | 37 14 7.4 0.20000 0.37838
> Pr(k >= 14) = 0.009277 (one-sided test)
> Pr(k <= 14) = 0.996629 (one-sided test)
> Pr(k <= 1 or k >= 14) = 0.011938 (two-sided test)
> . svret r, format(%8.2f)
> . l
> +----------------------------------------------------+
> | r_k_opp r_p r_k r_P_p r_N r_p_l r_p_u |
> |----------------------------------------------------|
> 1. | 1 0.01 14 0.20 37 1.00 0.01 |
> +----------------------------------------------------+
>
> I can't advise on exact syntax for -tabout-, which I don't use.
>
>
> Nick
> [email protected]
>
>
> On 24 January 2014 07:09, Michael McCulloch <[email protected]> wrote:
>> Thanks Nick & Richard,
>> Here's a shot at using -statsby- that gets me what I want.
>>
>> sysuse auto.dta, clear
>> gen group="a" if price<5000
>> replace group="b" if price>=5000
>> bitest foreign=.2 if group=="a"
>> bitest foreign=.2 if group=="b"
>> statsby, clear by(group): bitest foreign=.2
>> l group N p, clean noobs
>>
>>
>> Then I tried:
>>
>> sysuse auto.dta, clear
>> gen group=1 if price<5000
>> replace group=2 if price>=5000
>> levelsof group, local(levels)
>> foreach l of local levels {
>> bitest foreign=.2 if group == `l'
>> }
>> svret r, format(%8.2f)
>> l
>>
>> I have two questions:
>>
>> 1. Why in this -svret- attempt does the list return only the first value of group?
>> 2. Is it possible to use -tabout- to make the list into a nice table showing both values of group?
>>
>>
>> Best wishes,
>> Michael McCulloch
>>
>> --
>> Pine Street Foundation, since 1989
>> 124 Pine Street | San Anselmo | California | 94960-2674
>> P: (415) 407-1357 | F: (206) 338-2391 | http://www.PineStreetFoundation.org
>>
>> On Jan 23, 2014, at 10:33 AM, Richard Goldstein wrote:
>>
>>> true ;-)
>>>
>>> On 1/23/14, 1:22 PM, Nick Cox wrote:
>>>> I see, but you can just calculate that from the -statsby- results.
>>>>
>>>> Nick
>>>> [email protected]
>>>>
>>>>
>>>> On 23 January 2014 18:19, Richard Goldstein <[email protected]> wrote:
>>>>> 1. Michael, if you look at -h levelsof- there is an example showing its
>>>>> use with -foreach-
>>>>>
>>>>> 2. Nick, I did not suggest -statsby- because Michael asked for something
>>>>> that is not in the return list (r(k)/r(N)) and I don't think that this
>>>>> is allowed with -statsby-, but maybe I'm wrong about that?
>>>>>
>>>>> Rich
>>>>>
>>>>> On 1/23/14, 1:07 PM, Nick Cox wrote:
>>>>>> -search foreach- does exactly what you ask, namely point to sources on
>>>>>> -foreach-.
>>>>>>
>>>>>> But -help statsby- does even better.
>>>>>>
>>>>>> Here's a dopey example.
>>>>>>
>>>>>> sysuse auto, clear
>>>>>> statsby N=r(N) k=r(k) p_l=r(p_l) p_u=r(p_u) , by(rep78): bitest
>>>>>> foreign=.2
>>>>>> list
>>>>>>
>>>>>> Nick
>>>>>> [email protected]
>>>>>>
>>>>>> On 23 January 2014 17:55, Michael McCulloch <[email protected]>
>>>>>>
>>>>>>> Thank you Richard, that's exactly what I'm wanting to achieve.
>>>>>>> I understand now that -bysort- clears the scalars at each re-call.
>>>>>>>
>>>>>>> Can you point me to primers so I can learn how to wrap this into a -foreach- / -levelsof- loop?
>>>>>>
>>>>>>
>>>>>> On Jan 23, 2014, at 5:45 AM, Richard Goldstein wrote:
>>>>>>>
>>>>>>>> If I understand what you want correctly, you cannot do it with bysort
>>>>>>>> because each time you do the test the set of returned values (the
>>>>>>>> "r()"'s) will be replaced and the old ones lost
>>>>>>>>
>>>>>>>> you can do this within a -foreach- loop (you may need -levelsof- first)
>>>>>>>> in which you quietly do the -bitest- and then list your results for that
>>>>>>>> test and then do the next -bitest-, etc.
>>>>>>>>
>>>>>>>> here is an example of how to use the returned values:
>>>>>>>>
>>>>>>>> . sysuse auto
>>>>>>>>
>>>>>>>> . bitest foreign=.2
>>>>>>>>
>>>>>>>> Variable | N Observed k Expected k Assumed p Observed p
>>>>>>>> -------------+------------------------------------------------------------
>>>>>>>> foreign | 74 22 14.8 0.20000 0.29730
>>>>>>>>
>>>>>>>> Pr(k >= 22) = 0.029904 (one-sided test)
>>>>>>>> Pr(k <= 22) = 0.984075 (one-sided test)
>>>>>>>> Pr(k <= 7 or k >= 22) = 0.041800 (two-sided test)
>>>>>>>> r; t=0.09 8:39:38
>>>>>>>>
>>>>>>>> . di r(N) _skip(2) r(P_p) _skip(2) r(k)/r(N) _skip(2) r(p)
>>>>>>>> 74 .2 .2972973 .04179963
>>>>>>>>
>>>>>>>> I have not put headers on the columns and have not done several other
>>>>>>>> things you might want (e.g., print format for results) but this should
>>>>>>>> give the basic idea, assuming I have correctly understood you
>>>>>>
>>>>>> On 1/23/14, 12:57 AM, Michael McCulloch wrote:
>>>>>>
>>>>>>>>> I am using bitest for a two-sided test on whether the mean of varB is different than 0.2, and testing on each level of varA:
>>>>>>>>> bysort varA: bitest varB=.2
>>>>>>>>>
>>>>>>>>> varA has ~30 values. I wish to display these in a table (showing N, observed p,
>>>>>>>> expected p, and the two-sided p-value), without manual cut-and-paste, as
>>>>>>>> the test
>>>>>>>> will be used to monitor an ongoing training program.
>>>>>>>>>
>>>>>>>>> I note that the results of bitest are stored as:
>>>>>>>>> r(N) number N of trials
>>>>>>>>> r(P_p) assumed probability p of success
>>>>>>>>> r(k) observed number k of successes
>>>>>>>>> r(p_l) lower one-sided p-value
>>>>>>>>> r(p_u) upper one-sided p-value
>>>>>>>>> r(p) two-sided p-value
>>>>>>>>>
>>>>>>>>> However, I do not know how one uses these r(**) values. Can anyone suggest how one
>>>>>>>> would go about this?
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