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Re: st: R: one-sample t test query
From
Gwinyai Masukume <[email protected]>
To
[email protected]
Subject
Re: st: R: one-sample t test query
Date
Mon, 13 Jan 2014 13:06:00 +0200
Dear Phil and Carlo,
Many thanks for your help. Appreciated.
Thanks,
Gwinyai
On 1/13/14, Carlo Lazzaro <[email protected]> wrote:
> Dear Gwinyai,
> I would suggest to move from -ttest- to -prtest-, as your testing
> proportions (and not continuous variables):
>
> prtest sex_baby == 0.515 //sex_baby is 1 for males
>
> one-sample test of proportion sex_baby: Number of obs =
> 32
> ----------------------------------------------------------------------------
> --
> Variable | Mean Std. Err. [95% Conf.
> Interval]
> -------------+--------------------------------------------------------------
> --
> sex_baby | .375 .0855816 .207263
> .542737
> ----------------------------------------------------------------------------
> --
> p = proportion(sex_baby) z =
> -1.5846
> Ho: p = 0.515
>
> Ha: p < 0.515 Ha: p != 0.515 Ha: p >
> 0.515
> Pr(Z < z) = 0.0565 Pr(|Z| > |z|) = 0.1130 Pr(Z > z) =
> 0.9435
>
>
> Luckily enough, your conclusion is still valid: given your sample, there is
> no evidence that 37.5% is significantly different from 51.5% if p < 0.05 is
> considered significant.
>
> Kind regards,
> Carlo
> -----Messaggio originale-----
> Da: [email protected]
> [mailto:[email protected]] Per conto di Gwinyai Masukume
> Inviato: lunedì 13 gennaio 2014 10:22
> A: statalist
> Oggetto: st: one-sample t test query
>
> Hi Stata list,
>
> I have a dataset with 32 observations (20 females and 12 males). Males thus
> constitute 37.5% of the observations. Normally males should constitute
> 51.5%
> of the observations. I want to test if the observed 37.5% males are
> different from 51.5%. I have issued the following Stata command:
>
> . ttest sex_baby = 0.515
>
> One-sample t test
> ----------------------------------------------------------------------------
> --
> Variable | Obs Mean Std. Err. Std. Dev. [95% Conf.
> Interval]
> ---------+--------------------------------------------------------------
> ---------+------
> sex_baby | 32 .375 .086951 .4918694 .1976622
> .5523378
> ----------------------------------------------------------------------------
> --
> mean = mean(sex_baby) t =
> -1.6101
> Ho: mean = 0.515 degrees of freedom =
> 31
>
> Ha: mean < 0.515 Ha: mean != 0.515 Ha: mean >
> 0.515
> Pr(T < t) = 0.0588 Pr(|T| > |t|) = 0.1175 Pr(T > t) =
> 0.9412
>
> Looking at the two-tailed p-value, I conclude that 37.5% is not
> significantly different from 51.5% if p < 0.05 is considered significant.
> Have I used the correct Stata command and is my interpretation correct?
>
> Thanks,
> Gwinyai
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