Background
Cervical cancer is the fourth most common cancer in women worldwide (569,847 new cases, 6.6% out of total in 2018) and the eighth most common cancer overall (3.2% out of total), according to data from the World Health Organization [
1]. In 2018, there were 311,365 estimated deaths from cervical cancer worldwide, accounting for 7.5% of all cancer deaths in females [
1].
In Spain, 2584 new cases of cervical cancer were estimated for 2017, which represents 2.8% of all new female cancer cases, and the number of deaths reached 620 in 2016 (1.4% of all female cancer deaths) [
2]. Nowadays, Spain is one of the countries with the lowest incidence rates in the European Union, and also with one of the lowest rates of mortality [
3]. The reduction of incidence in recent years has been generally observed in high-income countries [
4].
Between one third and one half of cancer deaths can be avoided with prevention, early detection and treatment [
5]. The European guidelines for quality assurance in cervical cancer screening agree with implementing national population-based screening programs [
6]. At a regional level, some studies have shown that a cervical smear performed regularly is effective to improve the secondary prevention [
7,
8], while other studies have not found it cost-effective or suggested to redefine inclusion criteria [
9,
10]. In the Spanish National Health Service, where health care is regionally managed and delivered, prevention strategies developed in each region may differ. Screening programs are, unlike in other European countries, such as Italy, Netherlands or Sweden, mostly opportunistic (i.e. not systematically offered to target population, which usually lead to over-screening in more motivated women, and also to under-screening in less informed women) [
3], and their characteristics and inclusion criteria vary (for instance, some regional health services recommend to undertake a cytology every three years for all women aged 25–65, whilst others widen that period to five years for those aged over 35). Although both types of screening can reduce the incidence of cervical cancer, population-based ones show more equity and effectiveness [
11‐
15]. At the present time, only three Spanish regions have implemented a population-based screening program (Castilla y León, La Rioja and, more recently, Castilla-La Mancha) [
16‐
18], although some other regional governments have announced that they will also do during next years [
19‐
21].
The relationship between the use of health preventive services and different socio-demographic variables has been widely addressed in the literature. Previous studies have highlighted the relevance of socioeconomic variables on the probability of making use of breast and cervical screening [
14,
15,
22‐
29], and some have identified those factors contributing to income-related inequality of cervical screening [
22]. More recently, the evolution of frequency of cervical cytology testing, as well as its determinants, has also been studied [
30]. However, the degree of income-related inequality has not been quantified and determinants of inequality changes during the economic crisis remain unknown.
Spain has been one of the European countries where the Great Recession had a more remarkable impact on the health care system. Particularly, Spanish austerity policies lead to a decrease around 13% in public health expenditure from 2009 to 2013, and implied the implementation of several reforms, including a change in the existing entitlement rules [
31]. Spending cuts translated into an increase of waiting times and waiting lists. Waiting times for first visits to gynecologist increased from around 73 days before the crisis to 109 days in 2014, and the proportion of patients waiting for more than a month rose from 36.7 to 41.5% [
32,
33]. It has to be noticed that high waiting times were the main reason to declare unmet needs during the crisis, according to the Spanish National Health Surveys [
34,
35]. Also, a recent study has been shown how pro-rich inequities in unmet needs increased in Spain along the economic crisis, as well as pro-rich inequities in access to screening tests such as mammography [
36]. Some other studies have also identified an increase in pro-rich inequity related to publicly financed visits to specialists [
37,
38]. All these facts suggest that social inequalities in cervical cancer screening could have increased over the Great Recession.
This paper explicitly estimates the degree of income-related inequality in cytology testing for Spanish women in 2006 and 2011 by employing concentration indices, and decomposes changes in inequality in order to ascertain how the contribution of each explanatory factor has evolved over time. This approach has important policy implications since it could improve the design of actions to prevent cervix cancer while coping with inequalities. An additional contribution of this paper resides in the analysis of a period marked by the impact of the economic crisis.
Results
Table
1 shows the mean value of all the variables for both analyzed surveys. It is worth noting that the prevalence of women undergoing a cytology increased around 4 percentage points from 2006-07 (73.9%) to 2011–12 (77.9%). The comparison between both surveys also shows that the proportion of Spanish and married women decreased over time, as well as the household income level. Conversely, the proportion of women without private healthcare coverage, and the prevalence of physical inactivity and self-reported good health increased along the period. The rest of variables registered minor variations. However, it may be noticed that the proportion of population living in Catalonia and the Basque country show significant changes from one survey to another. In particular, according to the SHNS’s the percentage of Spaniards living in Catalonia would have significantly increased from 2006 to 07 to 2011–12, whilst the opposite would have happened in the Basque country.
According to our results, income-related inequality is statistically significant and favors the better-off in both periods. The corrected concentration indices point out that inequality significantly increased along the period, reaching 0.1726 in 2006–07 and 0.1880 in 2011–12 (p < 0.001).
Table
2 shows the contributions to inequality in cervical cancer screening for each year and the decomposition of total change. The three first columns for every year report the estimated partial effect retrieved from the probit model, the elasticity of cervical cancer screening for each explanatory variable and the concentration index for each regressor, respectively. Moreover, the fourth column shows the absolute contribution of each factor to overall income-related inequality, which is the product of the elasticity and the partial concentration index. A positive (negative) absolute contribution implies that, if inequality in cervical cancer screening was determined by that variable alone, then it would favor the better-off (worse-off). The fifth column reports the percentage contribution, which is obtained by dividing the absolute contribution by the overall income-related inequality (as measured by Erreygers CI). Finally, the last column of the table displays the absolute change in contributions from 2006-07 to 2011–12.
Table 2
Contributions to inequality in cervical cancer screening 2006–07 and 2011–12 and decomposition of total change
35–44 | 0.1299*** | 0.0518 | 0.1097 | 0.0057 | 3.3% | 0.0844*** | 0.0316 | 0.0285 | 0.0009 | 0.5% | −0.0048 |
45–54 | 0.1368*** | 0.0416 | −0.1588 | −0.0066 | −3.8% | 0.0857*** | 0.0281 | −0.0157 | − 0.0004 | − 0.2% | 0.0062 |
55–64 | 0.0383*** | 0.0102 | − 0.3293 | − 0.0033 | −1.9% | − 0.0195 | − 0.0049 | 0.1396 | − 0.0007 | − 0.4% | 0.0027 |
Spanish | 0.1463*** | 0.1819 | 0.0033 | 0.0006 | 0.3% | 0.1354*** | 0.1489 | 0.0756 | 0.0113 | 6.0% | 0.0107 |
Married | 0.1603*** | 0.1635 | −0.0568 | − 0.0093 | −5.4% | 0.0644*** | 0.0532 | −0.0346 | − 0.0018 | −1.0% | 0.0075 |
Ph_inact | −0.0444*** | − 0.0242 | − 0.2233 | 0.0054 | 3.1% | −0.0630*** | − 0.0381 | − 0.2474 | 0.0094 | 5.0% | 0.0040 |
Fair_health | 0.0409*** | 0.0141 | − 0.3630 | −0.0051 | −3.0% | 0.0242 | 0.0062 | −0.3064 | − 0.0019 | −1.0% | 0.0032 |
Bad_health | 0.0293 | 0.0022 | −0.5187 | − 0.0012 | − 0.7% | − 0.0345 | − 0.0023 | −0.5829 | 0.0014 | 0.7% | 0.0025 |
Verybad_health | 0.0531 | 0.0015 | −0.3333 | −0.0005 | − 0.3% | 0.0633 | 0.0010 | −0.7164 | − 0.0007 | − 0.4% | − 0.0002 |
Working | 0.0316*** | 0.0235 | 0.4497 | 0.0106 | 6.1% | 0.0395*** | 0.0292 | 0.4778 | 0.0139 | 7.4% | 0.0034 |
Educ2 | 0.0404*** | 0.0120 | 0.2691 | 0.0032 | 1.9% | 0.0478*** | 0.0155 | 0.1315 | 0.0020 | 1.1% | − 0.0012 |
Educ3 | 0.0463*** | 0.0190 | 1.1101 | 0.0211 | 12.2% | 0.0801*** | 0.0302 | 1.0825 | 0.0327 | 17.4% | 0.0116 |
Ln_eqincome | 0.1110*** | 1.0295 | 0.1053 | 0.1084 | 62.8% | 0.0711*** | 0.6094 | 0.1336 | 0.0814 | 43.3% | −0.0270 |
Public_ins | − 0.1122*** | − 0.1209 | − 0.2616 | 0.0316 | 18.3% | − 0.0471** | − 0.0490 | − 0.2434 | 0.0119 | 6.3% | − 0.0197 |
Region2 | 0.0610*** | 0.0021 | 0.3763 | 0.0008 | 0.5% | 0.0241 | 0.0009 | 0.7786 | 0.0007 | 0.4% | −0.0001 |
Region3 | 0.0408 | 0.0014 | 0.2910 | 0.0004 | 0.2% | 0.0077 | 0.0002 | 0.3192 | 0.0001 | 0.0% | −0.0003 |
Region4 | 0.1124*** | 0.0045 | 0.7439 | 0.0034 | 1.9% | 0.0905*** | 0.0029 | 0.3848 | 0.0011 | 0.6% | −0.0023 |
Region5 | 0.1155*** | 0.0081 | −0.7660 | −0.0062 | −3.6% | 0.1613*** | 0.0096 | −0.9279 | −0.0090 | −4.8% | − 0.0027 |
Region6 | −0.0031 | − 0.0001 | −0.2263 | 0.0000 | 0.0% | 0.0000 | 0.0000 | −0.0415 | 0.0000 | 0.0% | 0.0000 |
Region7 | 0.0582** | 0.0043 | −0.2247 | −0.0010 | − 0.6% | 0.0947*** | 0.0065 | 0.2429 | 0.0016 | 0.8% | 0.0025 |
Region8 | 0.0071 | 0.0004 | −0.4940 | − 0.0002 | −0.1% | 0.0600** | 0.0031 | −0.6753 | −0.0021 | −1.1% | − 0.0019 |
Region9 | 0.0285 | 0.0049 | 0.8364 | 0.0041 | 2.4% | 0.1326*** | 0.0270 | 0.6263 | 0.0169 | 9.0% | 0.0129 |
Region10 | 0.0089 | 0.0013 | 0.0693 | 0.0001 | 0.1% | 0.1101*** | 0.0155 | −0.1839 | −0.0028 | −1.5% | −0.0029 |
Region11 | −0.0369 | −0.0011 | −1.0699 | 0.0011 | 0.7% | 0.0196 | 0.0005 | −0.6949 | −0.0004 | − 0.2% | −0.0015 |
Region12 | 0.0400** | 0.0031 | −0.3635 | −0.0011 | − 0.7% | 0.0213 | 0.0016 | −0.4345 | − 0.0007 | −0.4% | 0.0004 |
Region13 | 0.0425** | 0.0083 | 0.6799 | 0.0056 | 3.3% | 0.0955*** | 0.0180 | 0.4617 | 0.0083 | 4.4% | 0.0027 |
Region14 | 0.0308 | 0.0013 | −0.5062 | −0.0007 | − 0.4% | 0.0824*** | 0.0033 | −0.4122 | − 0.0013 | −0.7% | − 0.0007 |
Region15 | 0.0963*** | 0.0018 | 0.6742 | 0.0012 | 0.7% | 0.0300 | 0.0005 | 1.0422 | 0.0005 | 0.3% | −0.0007 |
Region16 | 0.0786*** | 0.0066 | 0.4933 | 0.0033 | 1.9% | 0.0605** | 0.0037 | 0.8995 | 0.0033 | 1.8% | 0.0001 |
Region17 | 0.0095 | 0.0001 | 0.1690 | 0.0000 | 0.0% | 0.0976*** | 0.0008 | 0.4331 | 0.0004 | 0.2% | 0.0003 |
Region18 | −0.0554 | −0.0002 | −0.5003 | 0.0001 | 0.1% | 0.0432 | 0.0001 | −0.8504 | −0.0001 | 0.0% | −0.0002 |
Residual | | | | 0.0011 | 0.6% | | | | 0.0122 | 6.5% | 0.0111 |
Corrected CI | | | | 0.1726 | 100.0% | | | | 0.1880 | 100.0% | 0.0154 |
The partial effects shown in Table
2 indicate that, for both surveys, 35–54 years old, Spanish, working and married or living in couple women showed a significantly higher probability of cervical cancer screening, in comparison to those younger, foreigner, not working or living without a couple. Also, income and educational level were highly and positively associated with the use of cervical cancer screening. Conversely, being physically inactive in leisure time and lacking direct access to private specialists reduced the probability of cytology testing. Self-assessed health only appeared to be significant in 2006–07, when reporting fair health was positively related to the use of preventive services, compared to reporting good or very good health. There are also some other significant changes in the partial effects across the period. In particular, age and marital status showed a lower influence on cervical screening in 2011–12 compared to 2006–07, as well as the household income. However, having university studies was much more influent at the end of the period. Futhermore, most of regional dummies showed different effects from one period to another: in eight of them it was observed a noticeable increase in the partial effect, whilst a remarkable decrease was registered in other five.
Negative (positive) signs for corrected concentration indices in Table
2 indicate that the explanatory variables had a pro-poor (pro-rich) distribution. Most variables showed the expected sign. It is worth noting the change registered in the sign for the aged 55–64: the previously pro-poor distribution became pro-rich with the crisis, since this age group was relatively well covered by public benefits (mainly unemployment benefits that after expiring turned into retirement pensions), compared to the rest of population. Also, the significant reduction in the pro-rich distribution of women aged 35–44 reflects the strong impact of the economic recession on young cohorts. Some other variables registered observable changes in their concentration indices across the analyzed period, such as non-compulsory education (showing a decrease in its pro-rich distribution), nationality and income (both showing an increase). Further, according to the concentration index of the dummy
verybad_health, income-related inequalities in self-reported health seem to have suffered a remarkable rise across time.
According to our results, inequality in cytology testing was mainly explained by the direct effect of income in both periods, which accounted for 62.8% of the total in 2006–07 and for 43.3% in 2011–12. The (highly) negative contribution of income to total change shown in the last column of Table
2 indicates that its share in total inequality had (notably) decreased, despite the rise of inequality during the crisis. This is due to the lower elasticity of cervical screening with respect to income at the end of the period. The same effect is observed for having public insurance without direct access to private specialists. The type of health insurance, the educational level and the place of residence were ranked as the second (18.3%), third (14.1%) and fourth (6.3%) determinants of inequality, respectively, before the crisis started. However, in 2011–12 the rank of determinants slightly varied; the educational level occupied the second place (18.5%), followed by the region of residence (8.7%) and the working status (7.4%). All these factors tended to favor the better-off in both periods. This is also the case of nationality, whose contribution registered the highest increase (from 0.3 to 6%). The unexplained part of inequality, although higher in the final year compared to the beginning of the period, was low in both analyzed years, what indicates a good specification of the probit models.
Finally, Table
3 allows disentangling if changes over time were due to changes in elasticities of cytology testing with respect to its determinants, or due to changes in the concentration indices of regressors. For the age dummy 35–44, the type of insurance and some regions (the Balearic and the Canary Islands, and also Castilla-La Mancha), the changes in both components acted in the same direction, and tended to reduce pro-rich inequalities. For the age dummy, the main responsible of that effect was the significant decrease in the concentration index, whilst for the rest of the above-mentioned variables, the variation in their contribution to total inequality was due to changes in elasticities.
Table 3
Oaxaca-type decomposition for change in inequality (2006–2012)
35–44 | −0.0027 | −0.0020 | −0.0043 | −0.0005 | − 0.0048 | −31% |
45–54 | 0.0043 | 0.0019 | 0.0060 | 0.0002 | 0.0062 | 40% |
55–64 | −0.0024 | 0.0051 | 0.0047 | −0.0020 | 0.0027 | 17% |
Spanish | 0.0107 | −0.0001 | 0.0125 | −0.0018 | 0.0107 | 69% |
Married | 0.0013 | 0.0061 | 0.0039 | 0.0035 | 0.0075 | 48% |
Ph_inact | 0.0005 | 0.0036 | 0.0003 | 0.0038 | 0.0040 | 26% |
Fair_health | 0.0005 | 0.0028 | 0.0010 | 0.0022 | 0.0032 | 21% |
Bad_health | 0.0001 | 0.0024 | −00001 | 0.0026 | 0.0025 | 16% |
Verybad_health | −0.0004 | 0.0002 | −0.0005 | 0.0003 | −0.0002 | −1% |
Working | 0.0001 | 0.0032 | 0.0001 | 0.0033 | 0.0034 | 22% |
Educ2 | −0.0024 | 0.0012 | −0.0017 | 0.0005 | −0.0012 | −8% |
Educ3 | −0.0026 | 0.0142 | −0.0016 | 0.0131 | 0.0116 | 75% |
Ln_eqincome | 0.0138 | −0.0408 | 0.0222 | −0.0492 | −0.0270 | − 176% |
Public_ins | −0.0016 | − 0.0181 | − 0.0037 | −0.0160 | − 0.0197 | − 128% |
Region2 | 0.0003 | −0.0005 | 0.0008 | −0.0009 | − 0.0001 | −1% |
Region3 | 0.0000 | −0.0004 | 0.0000 | −0.0004 | −0.0003 | −2% |
Region4 | −0.0011 | −0.0011 | − 0.0017 | −0.0006 | − 0.0023 | −15% |
Region5 | −0.0012 | − 0.0016 | −0.0009 | − 0.0018 | −0.0027 | −18% |
Region6 | 0.0000 | 0.0000 | 0.0000 | 0.0000 | 0.0000 | 0% |
Region7 | 0.0031 | −0.0006 | 0.0020 | 0.0006 | 0.0025 | 16% |
Region8 | −0,0005 | −0.0014 | − 0.0001 | −0.0019 | − 0.0019 | −12% |
Region9 | −0.0069 | 0.0197 | −0.0012 | 0.0140 | 0.0129 | 84% |
Region10 | −0.0040 | 0.0010 | −0.0003 | −0.0026 | − 0.0029 | −19% |
Region11 | 0.0002 | −0.0017 | −0.0004 | − 0.0011 | −0.0015 | −10% |
Region12 | −0.0001 | 0.0005 | −0.0002 | 0.0006 | 0.0004 | 3% |
Region13 | −0.0046 | 0.0073 | −0.0020 | 0.0047 | 0.0027 | 17% |
Region14 | 0.0004 | −0.0011 | 0.0002 | −0.0008 | −0.0007 | −4% |
Region15 | 0.0002 | −0.0008 | 0.0006 | −0.0012 | −0.0007 | −4% |
Region16 | 0.0014 | −0.0013 | 0.0024 | −0.0023 | 0.0001 | 0% |
Region17 | 0.0002 | 0.0001 | 0.0000 | 0.0003 | 0.0003 | 2% |
Region18 | 0.0000 | −0.0002 | 0.0001 | −0.0003 | − 0.0002 | −1% |
Residual | | | | | 0,0111 | 72% |
Total | 0.0068 | −0.0025 | 0.0379 | −0.0336 | 0.0154 | 100% |
A second group of variables were those for which changes in elasticities and in concentration indices also acted in the same direction, but tended to increase pro-rich inequalities: this was the case for those variables representing women between 45 and 54 years old, marital status, physical inactivity, fair and bad health, and working status. Again, the registered changes in their contribution to inequality were mostly due to the impact of elasticities, except for the age variable.
Lastly, changes in elasticities and in concentration indices acted in different directions for those variables representing women between 55 and 64 years old, nationality, very bad health, educational level, income and most Spanish regions. The final effect implied that very bad health and income contributed to reduce pro-rich inequalities over time, whilst the rest of determinants of cervical screening contributed, in global terms, to their increase. The leading effect was due to changes in elasticities for the age dummy, educational level and income. The same holds true for Catalonia, the region showing the highest contribution to the increase of inequality over time. Conversely, the final impact of nationality and very bad health was mainly due to changes in their concentration indices.
According to the percentages shown in the last column of Table
3, income and the type of health insurance notably contributed to a reduction of pro-rich inequalities in cervical screening. However, their effect was more than compensated by the role played by other factors, such as nationality and the educational level. Also, the absolute contribution of the error term to the overall change of inequality significantly increased over time, since it accounted for 72% of total change, what implies that a meaningful part of the variation of inequality still remains unexplained.
Discussion
Our results show that income-related inequalities in cervical screening, which favor the better-off, significantly grew up from 2006-07 to 2011–12. This goes in line with some previous studies showing that Spanish pro-rich inequities in access to specialist doctors were intensified over the economic crisis [
37,
38], and also pro-rich inequalities in some other screening tests [
36]. However, our results indicate as well that the prevalence of cytology testing in Spain increased during the period 2006–2012, which is consistent with previous findings [
30]. The descriptive statistics of our sample also show changes in other variables that deserve some comment. For instance, the proportion of Spanish women notably decreased over time. Although the migration flows began to reverse after the economic crisis came up, the composition of population in 2011–12 significantly had changed compared to the previous decade, and the proportion of non-Spaniards had accordingly increased [
51]. The crisis impact also may be seen in the reduction of household income level and the slight increase of the proportion of women without private health coverage. Surprisingly, the prevalence of working women slightly grew up. This is compatible with a high increase of the unemployment rate for our sample of women (from 9.9% in 2006–07 to 16.7% in 2011–12), since what happened was that the category of students and homemakers notably reduced during the analyzed period (from around 28 to 21%). Also, the proportion of women reporting good or very good health significantly increased over time. It has been suggested that this fact could be due to that, during the Spanish crisis, other priorities ranked first compared to health [
52]. Lastly, it can be checked that the regional distribution of population in the SNHS 2006–07 is slightly different from official population statistics for that period. This problem only affects to Catalonia (that appears with a percentage of population lower than expected) and the Basque country (with a percentage higher than expected). This fact could be due to differences in the sample design for population statistics and health surveys.
The estimations obtained from our probit models are highly consistent with previous literature, which associates cervical screening with higher social status [
22‐
28,
30], educational level [
14,
22,
24,
25,
30,
53‐
57], self-perception of bad health [
58], middle-old age and not being foreign [
25,
26,
28,
30,
53‐
55,
58,
59], having a partner or being married [
14,
24,
25,
28,
30], being employed [
14,
24] or having private health insurance [
24,
25,
27,
28,
53,
55,
60,
61]. We also found that pro-rich-inequality is mainly explained by socioeconomic factors in both analyzed years, with income, educational level and working status playing an essential role in total inequality, in line with previous evidence about the patterns of use of preventive health care services [
13,
27].
After measuring income-related inequality in cervical screening and calculating the contribution of each relevant factor for both years, we used an Oaxaca-type decomposition in order to distinguish the effect of changes in elasticity of cytology testing with respect to its determinants, on one hand, from the impact of changes in inequalities in these factors, on the other. According to our results, change in inequalities is mainly due to changes in elasticities. That means that, despite the crisis, the distribution along income of most of the variables used in the analysis hardly varied from the beginning to the end of the period, although the influence of some factors significantly did. In particular, we found a stronger influence of higher education on the use of cervical screening and a decrease in the contribution of income. This fact could be pointing to the relevance of access to and ability to process information over other economic factors, such as the ability to pay, in the context of a National Health Service.
Also, the crisis seems to have significantly increased the influence of nationality on income-related inequality in cervical screening. At this point, it should be mentioned that the Spanish Government revoked previous full right to public health care coverage for undocumented migrants and some other groups through the Royal Decree-Law 16/2012, although it was unequally implemented by regional governments [
62]. However, despite the Decree entered into force before the data collection of SNHS 2011–12 had finished, this reform is expected to have a low impact on our results.
Nevertheless, we found that the influence of having direct access to private specialists noticeably decreased from 2006-07 to 2011–12, despite the rise in public waiting lists. This could be interpreted as a loss of relevance of some factors representing direct access barriers to health care, such as waiting time, in opposition to the role played by more subtle barriers, such as education or nationality.
Finally, we have shown that the region of residence has a not negligible influence on income-related inequality in cervical screening. Nevertheless, our results don’t seem to be systematically related to regional income, political sign or any other relevant variable at a regional level. Therefore, disentangling regional effects would deserve further research. Differences in contributions to inequality by regions might be related to the different response that every region gave to the crisis in terms of spending cuts and implementation of reforms promoted by the central government, which would be added to the previous significant differences in health care budget and management.
Our study has a number of limitations. Firstly, our estimated income variable may introduce some bias in the analysis, although we cannot predict in which direction inequality may be affected by the potential biases. Also, we restricted the analysis to a period when the crisis showed its biggest impact. More recent data are available for years 2014 and 2017, provided by the European Health Interview Survey (EHIS) and the new edition of the SNHS, respectively. However, both years correspond to a post-crisis period. Additionally, the information provided by the EHIS, which is referred to the first year of economic recovery, is not completely comparable to that retrieved from the SNHS.
Additionally, changes in elasticities shown in Table
2 could be further decomposed by using the total differential approach proposed by Wagstaff et al. (2003) [
41], in order to disentangle the effect of changes in the coefficients and the means of the regressors. We also performed this analysis, but since high approximation errors were obtained for most variables, we finally dismissed the results. It should be reminded that the total differential approach is only accurate for small changes, as it is based on an approximation. Moreover, it should be noted that, after the Oaxaca-type decomposition, an important part of the change in inequality remains unexplained. It could be suggested that some structural factors and contextual trends which are not captured by survey data could be explaining changes over time [
63], particularly if we consider that some major economic and social changes took place during the analyzed period. Also, other potential relevant variables such as wealth, which is not available in our dataset, could provide some explanatory power. However, and despite these limitations, our analysis still provides valuable insight about the factors behind the evolution of income-related inequality in cytology testing during the hardest years of crisis in Spain.