Question 3: Is there any evidence that induction of labour is related to the risk of a caesarean?
Induction of labour is a qualitative, dichotomous variable so we can do a chi-squared test or Fisher's exact test.
We get the following output:
| Induction of labour * Caesarian section Crosstabulation | ||||
|---|---|---|---|---|
| Count | ||||
| Caesarian section | Total | |||
| No | Yes | |||
| Induction of labour | No | 546 | 92 | 638 |
| Yes | 155 | 46 | 201 | |
| Total | 701 | 138 | 839 | |
| Chi-Square Tests | |||||
|---|---|---|---|---|---|
| Value | df | Asymp. Sig. (2-sided) | Exact Sig. (2-sided) | Exact Sig. (1-sided) | |
| Pearson Chi-Square | 7.971 a | 1 | .005 | ||
| Continuity Correctionb | 7.366 | 1 | .007 | ||
| Likelihood Ratio | 7.509 | 1 | .006 | ||
| Fisher's Exact Test | .006 | .004 | |||
| Linear-by-Linear Association | 7.961 | 1 | .005 | ||
| N of Valid Cases | 839 | ||||
| a. 0 cells (.0%) have expected count less than 5. The minimum expected count is 33.06.. | |||||
| b. Computed only for a 2x2 table | |||||
The chi-squared test is valid, because the expected frequencies are all greater than five. The relationship is highly significant (chi-squared = 7.97, d.f. = 1, P = 0.005). Hence there is strong evidence that caesarean section is related to induction of labour.
We can also find the odds ratio by choosing Risk from Statistics in Crosstabs. We get:
| Risk Estimate | |||
|---|---|---|---|
| Value | 95% Confidence Interval | ||
| Lower | Upper | ||
| Odds Ratio for Induction of labour (No / Yes) | 1.761 | 1.185 | 2.618 |
| For cohort Caesarian section = No | 1.110 | 1.023 | 1.204 |
| For cohort Caesarian section = Yes | .630 | .459 | .865 |
| N of Valid Cases | 837 | ||
Hence the odds ratio is 1.76 with 95% confidence interval 1.19 to 2.62.
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This page maintained by Martin Bland.
Last updated: 21 February, 2012.